A method for preparing and applying an amino acid-regulated polyamide nanofiltration membrane

Abstract

The invention discloses a method for preparing an amino acid-regulated polyamide nanofiltration membrane. The preparation method comprises the following steps: S1. mixing a base membrane with an aqueous solution, standing, removing the aqueous solution and drying; S2. mixing the base membrane after removing the aqueous solution in step S1 with an organic solution, standing, removing the organic solution, post-processing, and obtaining a polyamide nanofiltration membrane; the aqueous solution is a mixed solution of amino acids, piperazine and water; the organic solution is a mixed solution of polyacyl chlorides and organic solvents. The polyamide nanofiltration membrane prepared by the invention has high flux, excellent salt retention rate and stability, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of separation membranes, and more specifically, relates to a preparation method and application of an amino acid-regulated polyamide nanofiltration membrane. Background Art

[0002] Rational use and protection of water resources is an important and arduous task. Membrane separation technology, especially nanofiltration (NF), has good prospects in water treatment. The average molecular weight cutoff (MWCO) of nanofiltration membranes is 200-1000Da, which is between reverse osmosis (RO) and ultrafiltration (UF) membranes. The surface is usually negatively charged and can effectively separate divalent / monovalent inorganic salts. It has broad application prospects in the fields of seawater desalination, high-salt wastewater desalination and resource recovery, sewage treatment and drinking water purification. At present, the existing commercial nanofiltration membranes are mainly thin-layer composite (TFC) membranes prepared by interfacial polymerization, that is, water-phase amine monomers and oil-phase acyl chloride monomers are generated on the surface of ultrafiltration or microfiltration base membranes through interfacial polymerization to form a polyamide selective layer. Because the interfacial polymerization reaction is rapid and difficult to control, the prepared polyamide nanofiltration membranes often face the "trade-off" effect that the permeability and selectivity cannot be improved at the same time.

[0003] In existing research, the modification method of regulating interfacial polymerization by adding additives to the aqueous phase has the characteristics of simple operation and easy integration with the production line, and has attracted widespread attention from researchers. A variety of aqueous phase additives such as graphene oxide (GO), carbon quantum dots, metal-organic frameworks (MOFs), and plant polyphenols are used. These additives regulate the diffusion rate of amine monomers or affect the reaction between amine monomers and acyl chloride monomers, thereby achieving the regulation of the polyamide selection layer. However, the synthesis process of nanomaterials such as GO, carbon quantum dots, and MOFs is complicated, involving strong acids, high temperatures, and high pressures, and is not an environmentally friendly preparation technology; at the same time, these nanomaterials lack stability in the membrane separation layer and have the risk of dissolution toxicity. In addition, the reaction rate of the phenolic hydroxyl group of plant polyphenol compounds with acyl chlorides is slow, and usually requires an alkaline catalyst, and the amide layer formed has a low degree of cross-linking, resulting in a reduced retention rate.

[0004] Amino acids are organic compounds that contain both a basic amino group and an acidic carboxyl group. They are the basic building blocks of biological functional macromolecule proteins. Amino acids are widely available, with more than 300 species in nature. They are also easy to synthesize in a variety of ways and at low prices. The unique amphoteric characteristics and diversity of amino acids have attracted attention because amino acids have both amino and carboxyl groups and the amino group is reactive, making them an ideal substitute for interfacial polymerization amine monomers. At present, some studies have applied them to the preparation of separation membranes.

[0005] In the literature [Xu, R. et al. Influence of l-lysine on the permeation and antifouling performance of polyamide thin film composite reverse osmosis embednes. RSC Adv. 8, 25236-25247 (2018)], lysine was added to an aqueous solution of m-phenylenediamine (MPD) and interfacially polymerized with 1,3,5-trimethylbenzenecarboxylic acid chloride to prepare a polyamide reverse osmosis membrane. When the optimal addition amount reached 0.1wt%, the pure water flux of the membrane increased by 18% compared with the control group, and the sodium chloride retention rate increased from the original 98.17% to 98.40%. In the literature [Xu, R. et al. Preparation and performance of a charge-mosaic nanofiltration membrane with novel salt concentration sensitivity for the separation of salts and dyes. J. Membr. Sci. 595, 117472 (2020)], lysine was directly used as an amine monomer and 1,3,5-benzenetricarbonyl chloride to prepare a loosely structured polyamide nanofiltration membrane, and applied to the salt / dye separation system. However, its pure water flux was slightly lower than that of the control group polyamide membrane formed by piperazine and acyl chloride monomers. This may be because the polyamide membrane formed by lysine has a loose structure, which is compacted during high-pressure filtration (6 bar), resulting in a decrease in pure water flux. In addition, due to its loose structure, the MWCO is 1150-2775Da. Even under optimal conditions, the sodium sulfate retention rate of the nanofiltration membrane is only 78.36%.

[0006] It can be seen that the existing amino acid-modified polyamide nanofiltration membrane solutions have little effect on improving the performance of the polyamide separation layer, and it is difficult to achieve excellent permeability and selectivity at the same time. Therefore, how to develop a polyamide nanofiltration membrane with high flux (permeability), excellent selectivity (salt retention rate) and stability to break the traditional "trade-off" effect has broad application prospects. Summary of the invention

[0007] In view of the above-mentioned existing technical problems, the primary purpose of the present invention is to provide a method for preparing an amino acid-regulated polyamide nanofiltration membrane, in which amino acids are introduced as additives into a piperazine aqueous solution. The amino acids as additives not only regulate the process of interfacial polymerization but also participate in interfacial polymerization as monomers. The prepared polyamide nanofiltration membrane has a high flux, excellent salt retention rate and stability, breaking the traditional "trade-off" effect and having broad application prospects.

[0008] The second object of the present invention is to provide a polyamide nanofiltration membrane prepared by the above preparation method.

[0009] The third object of the present invention is to provide the use of the above-mentioned polyamide nanofiltration membrane in seawater desalination, divalent salt / monovalent salt separation in high-salt wastewater, wastewater volume reduction and / or water resource recovery.

[0010] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0011] A method for preparing an amino acid-regulated polyamide nanofiltration membrane comprises the following steps:

[0012] S1. The base film is mixed with the aqueous solution, allowed to stand, and the aqueous solution is removed and then dried;

[0013] S2. The base film after removing the aqueous phase solution in step S1 is mixed with the organic phase solution, allowed to stand, the organic phase solution is removed, and the polyamide nanofiltration membrane is obtained by heating;

[0014] The aqueous phase solution is a mixed solution of amino acids, piperazine and water;

[0015] The organic phase solution is a mixed solution of polyacid chloride and an organic solvent.

[0016] In the present invention, amino acids are used as additives to simultaneously participate in the interfacial polymerization reaction and the process of regulating the interfacial polymerization, thereby preparing a high-performance polyamide nanofiltration membrane. In the present invention, the carboxyl group of the amino acid has a significant electrostatic attraction with the protonated piperazine monomer due to its negative charge, which may lead to a decrease in the rate at which the piperazine monomer diffuses into the organic phase. At the same time, since the amino group in the amino acid is reactive, it can react with benzoyl trichloride to generate a looser structure than polyamine (piperazine), further hindering the reaction of piperazine with the organic monomer. Finally, the separation layer of the nanofiltration membrane prepared is thinner than that of the nanofiltration membrane prepared using the piperazine monomer alone, greatly shortening the water molecule transmission distance of the nanofiltration membrane during the application process, thereby improving the flux of the nanofiltration membrane.

[0017] Secondly, since the amino group reactivity of amino acids is lower than that of piperazine, amino acids play a regulatory role in interfacial polymerization and are not the main monomers of interfacial polymerization, so that the prepared polyamide membrane is still within the nanofiltration range, and will not expand to the range of loose nanofiltration membranes, thereby ensuring that the prepared polyamide nanofiltration membrane has excellent salt retention rate and smaller pore size. In addition, due to the presence of the carboxyl group of the amino acid itself, the surface negative charge of the membrane will be significantly improved, showing a good retention effect when conducting negative divalent salt retention, while improving the hydrophilicity of the polyamide membrane. After adding amino acids, the surface of the prepared nanofiltration membrane has more spherical morphology, which increases the water flow area of ​​the membrane to a certain extent. This uniform spherical morphology will be lower in roughness than traditional polyamide to a certain extent, reducing the degree of membrane contamination.

[0018] The polyamide nanofiltration membrane prepared by the present invention uses amino acids as additives, and has good salt retention rate and permeability, wherein the Na2SO4 retention rate is as high as 99.3%, and the membrane permeability of the three amino acids can reach up to 19.2L m -2 h - 1 bar -1 The present invention uses amino acids as additives, which are natural organic small molecule substances, are environmentally friendly, have a wide range of raw material sources and are cheap, and have wide applicability.

[0019] Preferably, the amino acid is selected from one or more of acidic polar amino acids, basic polar amino acids and neutral polar amino acids.

[0020] More specifically, the amino acids of the present invention include but are not limited to the following types:

[0021] Acidic amino acids: aspartic acid (Asp), glutamic acid (Glu).

[0022] Basic amino acids: lysine (Lys), arginine (Arg), histidine (His).

[0023] Neutral amino acids: glutamine (Gln), serine (Ser), threonine (Thr), cysteine ​​(Cys), asparagine (Asn), tyrosine (Tyr), and glycine (Gly).

[0024] More preferably, the amino acid is selected from one or more of lysine, cysteine, glutamic acid, histidine and serine.

[0025] Preferably, the mass volume ratio of the amino acid to deionized water is (1-10):1 g / L; the mass volume ratio of piperazine to water is (1-5):1 g / L.

[0026] In some embodiments, when the amino acid is lysine, the mass volume ratio of the amino acid to water is (5-10): 1 g / L; the mass volume ratio of piperazine to water is (2-4): 1 g / L. Under this preferred condition, the prepared polyamide nanofiltration membrane has higher water flux and salt rejection rate.

[0027] In some embodiments, when the amino acid is cysteine, the mass volume ratio of the amino acid to deionized water is (3-7): 1 g / L; the mass volume ratio of piperazine to water is (2-4): 1 g / L. Most preferably, the mass volume ratio of the amino acid to deionized water is 5: 1 g / L; the mass volume ratio of piperazine to water is 2: 1 g / L. Under this preferred condition, the polyamide nanofiltration membrane prepared has higher water flux and salt rejection rate.

[0028] In some embodiments, when the amino acid is glutamic acid, the mass volume ratio of the amino acid to deionized water is (5-10): 1 g / L; the mass volume ratio of piperazine to water is (2-4): 1 g / L. Further preferably, the mass volume ratio of the amino acid to deionized water is 7: 1 g / L; the mass volume ratio of piperazine to water is 2: 1 g / L. Under this preferred condition, the prepared polyamide nanofiltration membrane has higher water flux and salt rejection rate.

[0029] Preferably, the mass volume ratio of the polyacid chloride to the organic solvent is (0.5-2.5):1 g / L. Further preferably, the mass volume ratio of the polyacid chloride to the organic solvent is (1-2):1 g / L.

[0030] Preferably, the polyacid chloride is selected from one or more of 1,3,5-trimesoyl chloride, terephthaloyl chloride or isophthaloyl chloride. More preferably, the polyacid chloride is 1,3,5-trimesoyl chloride.

[0031] Preferably, the base film is polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile, polyethylene, polyvinyl chloride or polytetrafluoroethylene.

[0032] Preferably, the organic solvent is selected from one or more of n-hexane, n-decane, petroleum ether, n-heptane, and cyclohexane. Further preferably, the organic solvent is n-hexane.

[0033] Preferably, in step S1, the standing time is 1 to 10 minutes; in step S2, the standing time is 0.5 to 3 minutes. Further preferably, in step S1, the standing time is 3 to 7 minutes; in step S2, the standing time is 1 to 2 minutes.

[0034] Preferably, the post-treatment includes a cleaning treatment and a drying treatment. More specifically, the treated base film is cleaned with the above-mentioned organic solvent to remove the organic phase solution on the surface of the base film. More specifically, the drying treatment is performed at 40-70°C.

[0035] Preferably, the aqueous phase solution is obtained by the following preparation method: piperazine and amino acid are stirred and mixed, and then the pH is adjusted to 10-11.5 to obtain the aqueous phase solution. The pH is adjusted to make the mixed solution consistent with the aqueous phase solution of a single piperazine monomer in the same mass volume ratio, thereby obtaining the aqueous phase solution. More specifically, the piperazine is anhydrous piperazine.

[0036] More preferably, the stirring speed is 200-300 rpm, and the stirring time is 10-30 min.

[0037] Furthermore, the present invention seeks to protect the polyamide nanofiltration membrane prepared by the above preparation method.

[0038] Furthermore, the present invention seeks to protect the use of the above-mentioned polyamide nanofiltration membrane in seawater desalination, divalent salt / monovalent salt separation in high-salt wastewater, wastewater volume reduction and / or water resource recovery processes.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] Compared with the traditional polyamide nanofiltration membrane preparation process, the present invention does not introduce additional operations. It only needs to add different types of amino acids as additives to the piperazine aqueous phase solution. The amino acids as additives not only regulate the process of interfacial polymerization but also participate in interfacial polymerization as monomers, so that the surface electronegativity and hydrophilicity of the polyamide nanofiltration membrane are significantly improved, and the thickness of the selective layer is significantly reduced, so that the polyamide membrane has a higher flux, excellent salt rejection rate, smaller pore size and stability at the same time, breaking the traditional "trade-off" effect and having broad application prospects. The polyamide membrane prepared by the present invention has a water flux of ≥8.6L m -2 h -1 bar -1 , Na2SO4 retention rate ≥95.6%. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a scanning electron microscope image of the cross section of the polyamide nanofiltration membrane prepared in Examples 3, 5, 8, 10, 13, 15 and Comparative Example 1.

[0042] Figure 2 It is a planar scanning electron microscope image of the polyamide nanofiltration membrane prepared in Examples 3, 5, 8, 10, 13, 15 and Comparative Example 1.

[0043] Figure 3Surface electronegativity test diagram of the polyamide nanofiltration membrane prepared in Examples 3, 5, 8, 10, 13, 15 and Comparative Example 1.

[0044] Figure 4 The carboxyl density on the surface of the polyamide nanofiltration membrane prepared in Examples 3, 5, 8, 10, 13, 15 and Comparative Examples 1 and 5. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with the accompanying drawings and specific examples, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0046] Example 1 Preparation of polyamide nanofiltration membrane

[0047] (1) 2.0 g of anhydrous piperazine and 1.0 g of lysine (amino acid purchased from Macklin, CAS: 56-87-1, with a structural formula shown in the following formula (I)) were added to 1 L of aqueous solution, and stirred at a stirring speed of 250 rpm for 15 min. At the same time, 5 mol / L of NaOH was added dropwise to adjust the pH to 10.95-11.05 to obtain an aqueous phase solution (the pH of the mixed solution was adjusted to be consistent with that of a single piperazine monomer aqueous phase solution having the same mass volume ratio).

[0048]

[0049] (2) Pour 50.0 mL of the aqueous solution prepared in step (1) onto the surface of the polysulfone ultrafiltration base membrane, let it stand for 5 minutes, then pour out the solution, absorb the remaining aqueous solution droplets with dust-free paper, let it stand for 3 minutes to dry, and obtain a piperazine-amino acid adsorbed polysulfone ultrafiltration base membrane.

[0050] (3) Add 2.0 g of 1,3,5-trimethylbenzenecarboxylic acid chloride to 1 L of n-hexane, stir for 20 min to dissolve completely to obtain an organic phase solution, pour 50 mL of the organic phase solution onto the surface of the polysulfone ultrafiltration base membrane treated in step (2) and let it stand for 1 min to perform interfacial polymerization; then pour out the organic phase solution on the membrane surface, pour in n-hexane solvent to wash and remove the unreacted 1,3,5-trimethylbenzenecarboxylic acid chloride on the surface of the base membrane, place it in an oven at 60°C for heat treatment for 10 min to obtain a polyamide nanofiltration membrane, take it out, rinse it with pure water three times, and soak it in pure water for low temperature storage.

[0051] Example 2 Preparation of polyamide nanofiltration membrane

[0052] The difference between this embodiment and embodiment 1 is that in step (1), the amount of lysine added is 3.0 g.

[0053] Example 3 Preparation of polyamide nanofiltration membrane

[0054] The difference between this embodiment and embodiment 1 is that in step (1), the amount of lysine added is 5.0 g.

[0055] Example 4 Preparation of polyamide nanofiltration membrane

[0056] The difference between this embodiment and embodiment 1 is that in step (1), the amount of lysine added is 7.0 g.

[0057] Example 5 Preparation of polyamide nanofiltration membrane

[0058] The difference between this embodiment and embodiment 1 is that in step (1), the amount of lysine added is 10.0 g.

[0059] Example 6 Preparation of polyamide nanofiltration membrane

[0060] The difference between this embodiment and embodiment 1 is that in step (1), the amino acid added in step (1) is cysteine ​​(the amino acid is purchased from Macklin, CAS: 52-90-4, and its structural formula is shown in the following formula (II)).

[0061]

[0062] Example 7 Preparation of polyamide nanofiltration membrane

[0063] The difference between this embodiment and embodiment 6 is that in step (1), the amount of cysteine ​​added is 3.0 g.

[0064] Example 8 Preparation of polyamide nanofiltration membrane

[0065] The difference between this embodiment and embodiment 6 is that in step (1), the amount of cysteine ​​added is 5.0 g.

[0066] Example 9 Preparation of polyamide nanofiltration membrane

[0067] The difference between this embodiment and embodiment 6 is that in step (1), the amount of cysteine ​​added is 7.0 g.

[0068] Example 10 Preparation of polyamide nanofiltration membrane

[0069] The difference between this embodiment and embodiment 6 is that in step (1), the amount of cysteine ​​added is 10.0 g.

[0070] Example 11 Preparation of polyamide nanofiltration membrane

[0071] The difference between this embodiment and embodiment 1 is that in step (1), the amino acid added is glutamic acid (the amino acid is purchased from Macklin, CAS: 56-86-0, and its structural formula is shown in the following formula (III)).

[0072]

[0073] Example 12 Preparation of polyamide nanofiltration membrane

[0074] The difference between this embodiment and embodiment 11 is that in step (1), the amount of glutamic acid added is 3.0 g.

[0075] Example 13 Preparation of polyamide nanofiltration membrane

[0076] The difference between this embodiment and embodiment 11 is that in step (1), the amount of glutamic acid added is 5.0 g.

[0077] Example 14 Preparation of polyamide nanofiltration membrane

[0078] The difference between this embodiment and embodiment 11 is that in step (1), the amount of glutamic acid added is 7.0 g.

[0079] Example 15 Preparation of polyamide nanofiltration membrane

[0080] The difference between this embodiment and embodiment 11 is that in step (1), the amount of glutamic acid added is 10.0 g.

[0081] Example 16 Preparation of polyamide nanofiltration membrane

[0082] The difference between this embodiment and embodiment 3 is that in step (1), the amino acid added is histidine (the amino acid is purchased from Macklin, CAS: 71-00-1, and its structural formula is shown in the following formula (IV)).

[0083]

[0084] Example 17 Preparation of polyamide nanofiltration membrane

[0085] The difference between this embodiment and embodiment 3 is that in step (1), the amino acid added is serine (the amino acid is purchased from Macklin, CAS: 56-45-1, and its structural formula is shown in the following formula (V)).

[0086]

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 1 is that in step (1), no amino acid is added.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 5 is that in step (1), piperazine is not added.

[0091] Comparative Example 3

[0092] The difference between this comparative example and Example 8 is that in step (1), piperazine is not added.

[0093] Comparative Example 4

[0094] The difference between this comparative example and Example 15 is that in step (1), piperazine is not added.

[0095] Comparative Example 5

[0096] The commercial polyamide nanofiltration membrane used in this comparative example is Filmtec TM NF270.

[0097] Comparative Example 6

[0098] The difference between this comparative example and Example 3 is that in step (1), the amine monomer used is polyethyleneimine, and the amount used is 5 g / L; in step (3), the amount of 1,3,5-benzenetricarboxylic acid chloride used is 1 g / L.

[0099] Comparative Example 7

[0100] The difference between this comparative example and Example 13 is that in step (1), the amine monomer used is polyethyleneimine, and the amount used is 5 g / L; in step (3), the amount of 1,3,5-benzenetricarboxylic acid chloride used is 1 g / L.

[0101] Comparative Example 8

[0102] The difference between this comparative example and Example 3 is that in step (1), the amine monomer used is m-phenylenediamine, and the amount used is 1 g / L; in step (3), the amount of 1,3,5-benzenetricarboxylic acid chloride used is 1 g / L.

[0103] Comparative Example 9

[0104] The difference between this comparative example and Example 13 is that in step (1), the amine monomer used is m-phenylenediamine, and the amount used is 1 g / L; in step (3), the amount of 1,3,5-benzenetricarboxylic acid chloride used is 1 g / L.

[0105] Test Example 1 Characterization of polyamide nanofiltration membrane

[0106] The polyamide nanofiltration membrane synthesized in the embodiment and the comparative example was observed for surface morphology and cross-section using a high-resolution cold field emission scanning electron microscope (FESEM, model: Regulus8230), and the nanofiltration membranes of the embodiments 3, 5, 8, 10, 13, 15 and the comparative example 1 at the same amino acid concentration were selected for cross-section observation. The polyamide nanofiltration membrane was dried with a freeze-drying agent in advance, and before the plane morphology observation, the conductive adhesive was attached to the sample copper table, and the membrane sample was cut to a suitable size and then neatly attached to the conductive adhesive; before the cross-section observation of the membrane, it was quenched with liquid nitrogen, and then the quenched membrane sample was attached to the vertical surface of the copper table attached with the conductive adhesive, with the cross section facing outward and vertically upward, and then the sample surface was sprayed with gold and observed at an accelerating voltage of 5kV.

[0107] Figure 1 The cross-sectional scanning electron microscope images of the polyamide nanofiltration membranes prepared in Examples 3, 5, 8, 10, 13, 15 and Comparative Example 1 are shown in FIG. Figure 2 The planar scanning electron microscope images of the polyamide nanofiltration membranes prepared in Examples 3, 5, 8, 10, 13, 15 and Comparative Example 1 are shown. Figure 1 It can be seen that the selective layers of the membranes prepared in Examples 3, 5, 8, 10, 13, and 15 are much thinner than the polyamide nanofiltration membrane prepared in Comparative Example 1. On the one hand, this is because the amino acid limits the diffusion of piperazine through intermolecular forces, making the generated polyamide membrane thinner; on the other hand, the amino group of the amino acid can react with the acyl chloride monomer, limiting the piperazine monomer and the acyl chloride monomer to form a thick and dense polyamide layer. Figure 2 It can be seen that the surfaces of all polyamide nanofiltration membranes are spherical nodules. After the addition of amino acids, as the content of the three amino acids increases from 5.0 g / L to 10.0 g / L, the spherical structure of the membrane becomes denser and smaller. While a defect-free polyamide membrane is generated, the uniformity of the polyamide nanofiltration membrane surface is improved and the specific surface area of ​​the selective layer is increased.

[0108] Test Example 2 Characterization experiment of membrane surface electronegativity of polyamide nanofiltration membrane

[0109] The surface electronegativity of the polyamide nanofiltration membranes prepared in Examples 3, 5, 8, 10, 13, 15 and Comparative Example 1 was tested using an electric solid surface analyzer (model: SurPASS 3, Anton Paar) to understand the charge status of the membrane surface. The polyamide membrane was cut to a suitable size and attached to a pair of sample stages. After adjusting the gap height to the appropriate position, a scanning test was performed in a 1mmol / L KCl buffer solution. The pH of the solution in contact with the membrane surface was regulated by dripping acid and alkali standard solutions. The pH range of the scanning test was 3 to 10. The results are shown in Figure 3 .

[0110] The carboxyl content of the membrane surface can be quantified by toluidine blue O (TBO) titration. TBO is a cationic compound that can electrostatically interact with negatively charged groups and be detected by developing a blue color. In the present invention, the polyamide nanofiltration membranes of Examples 3, 5, 8, 10, 13, 15 and Comparative Example 1 are fixed on a clean glass plate with the selection layer facing upward. At room temperature (25°C), the polyamide nanofiltration membrane is contacted with a TBO solution (dissolved in a NaOH solution system with a pH of 11) for a period of time, and then the membrane is removed and rinsed with deionized water until the water flow is colorless to wash away unbound TBO molecules. Further, the membrane is placed in a certain volume of 0.2 mol / L NaCl solution with a pH of 2 (adjusted with hydrochloric acid), stirred at 250 rpm for 30 minutes for decolorization, and further, the absorbance of the resulting solution is measured and analyzed at a wavelength of 633 nm. The absorption is converted into TBO concentration using a calibration curve, and the carboxyl density on the membrane surface is calculated by dividing the number of TBO molecules by the membrane plane area. The results are shown in Figure 4 .

[0111] pass Figure 3 , Figure 4 It can be seen that due to the introduction of amino acid carboxyl groups, the surface negative charge of the polyamide nanofiltration membrane is greatly enhanced, and at the same time, the surface carboxyl content of the polyamide nanofiltration membrane is significantly increased, which is beneficial to the retention of negatively charged ions by the polyamide nanofiltration membrane.

[0112] Test Example 3: Pure water permeation flux, salt rejection rate and average molecular weight cutoff experiment of polyamide nanofiltration membrane

[0113] The pure water permeability and sodium sulfate rejection rate of the polyamide nanofiltration membrane prepared in the comparative example and the embodiment were tested, and the specific implementation method is as follows:

[0114] (1) Pure water flux test

[0115] The cross-flow filtration device (Fujian Xiamei Technology) was used for the experiment. The basic experimental parameters were as follows: the effective area of ​​the membrane was 4×10 -3 m -2 The water temperature of the cross-flow filtration experiment was controlled at 24.6±0.4℃ and the test pressure was 5bar. During the test, pure water was used as the feed liquid. The prepared series of polyamide nanofiltration membranes were pre-pressed at 5bar pressure for 30min to make the membrane flux basically stable. The change of the effluent volume within at least 5min was recorded by the instrument. The permeation flux Flux (L m -2 h -1 bar -1 ):

[0116]

[0117] In the above formula, V is the volume of the permeate, m 3 ; A is the effective cross-flow area of ​​the membrane pool, m 2 ; t is the cross-flow filtration time of pure water after stabilization, h; ΔP is the operating pressure of the device, bar.

[0118] (2) Determination of salt retention rate

[0119] The salt rejection effect of the polyamide nanofiltration membrane prepared in the embodiment and the comparative example can be obtained by conducting a filtration experiment using a cross-flow filtration device.

[0120] In the scheme, a 1000 mg / L sodium sulfate solution was prepared as the original solution for interception test, and the test object was the polyamide nanofiltration membrane prepared in the embodiment and the comparative example. The feed liquid was pre-pressed for 30 min under 5 bar conditions to stabilize the flux, and then the concentrate and permeate were collected for testing, and their conductivity was tested respectively. The salt retention rate R (%) was calculated by the following formula:

[0121]

[0122] Among them, C f and C p Represent the conductivity values ​​of the concentrate and permeate, μS / cm, respectively.

[0123] The test comparison results of pure water flux and various salt rejection rates of the polyamide nanofiltration membranes prepared in the comparative example and the example are shown in Table 1.

[0124] (3) Determination of average molecular weight cut-off

[0125] The average molecular weight cutoff of the polyamide nanofiltration membranes prepared in the examples and comparative examples can be obtained by conducting filtration experiments using a cross-flow filtration device.

[0126] In the scheme, 200 mg / L polyethylene glycol (PEG) solutions with molecular weights of 200, 300, 400, 600, and 800 Da were prepared as feed liquids, and the test objects were polyamide nanofiltration membranes prepared in the embodiments and comparative examples. The feed liquid was pre-pressed for 30 min under 5 bar conditions to stabilize the flux, and then the concentrate and permeate were collected for testing, and the concentration of PEG in the concentrate and permeate was determined by a total organic carbon analyzer (TOC). The retention rate (R) was calculated as follows:

[0127]

[0128] In the formula, TOC P and TOC R Represent the concentrations of PEG in the permeate and concentrate, respectively.

[0129] Table 1

[0130]

[0131]

[0132] From the data in Table 1, it can be seen that the polyamide nanofiltration membrane prepared by the present invention has good permeability and high sodium sulfate retention rate. The water flux of the polyamide membrane prepared by the present invention is ≥8.6L m -2 h -1 bar -1 , Na2SO4 rejection rate ≥ 95.6%. Furthermore, the water flux of the polyamide membrane prepared by the present invention is ≥ 12.2 L m -2 h -1 bar -1 , Na2SO4 retention rate ≥97.8%.

[0133] It can be seen from Examples 1 to 15 and Comparative Examples 2, 3, and 4 that the nanofiltration membrane generated by the reaction of the three amino acids themselves with 1,3,5-trimethylbenzenecarboxylic acid chloride is loose, and the required effect of salt interception cannot be achieved, and some nanofiltration membranes cannot be formed. Compared with Comparative Example 1, the nanofiltration membrane prepared without using amino acids as additives has a "trade-off" effect between salt retention rate and permeability, while the polyamide nanofiltration membrane in which the three amino acids participate in interfacial polymerization improves the retention rate and permeability of the membrane at the same time. Examples 5, 8, and 15 are the most preferred among the three amino acids.

[0134] Among them, in the embodiment that can maintain a high salt retention rate, Example 5 has a maximum permeate flux of 19.2Lm -2 h - 1 bar -1 , which is 3.5 times that of comparative example 1, while example 14 has the highest salt rejection rate of 99.3%. The increase in water flux and the maintenance of salt rejection of the nanofiltration membrane prepared in the example are due to the enhancement of the negative charge of the nanofiltration membrane and the reduction of the thickness of the selective layer.

[0135] Furthermore, the average molecular weight (MWCO) of the polyamide nanofiltration membranes of Examples 3, 5, 8, 10, 13, 15 and Comparative Example 1 was tested. The results are shown in Table 2 below.

[0136] Table 2

[0137] Serial number Average molecular weight (MWCO, Da) Example 3 380.44 Example 5 407.93 Example 8 421.07 Example 10 600 Embodiment 13 388.71 Embodiment 15 398.75 Comparative Example 1 362.99

[0138] It can be seen from Table 2 that, compared with Comparative Example 1, the average molecular weight cutoffs of Examples 3, 5, 8, 13, and 15 only slightly increased, with little change, and still had smaller pore sizes.

[0139] This invention also illustrates that under the premise of using specific polyamine monomers, most water-soluble amino acids can be used as ideal water-phase additives to prepare high-performance polyamide nanofiltration membranes with strong negative charge. However, the molecular structure characteristics of the specific amino acids need to be considered during implementation. For example, in Examples 6 to 10, cysteine ​​has the best performance at an addition amount of 5.0 g / L due to its spatial structure. In Example 16, histidine has a relatively large benzene ring structure, which significantly hinders the formation process of the polyamide membrane and the overall performance of the membrane is lower than that of other examples.

[0140] It can be seen from the embodiments and comparative examples 6 to 7 and comparative examples 8 to 9 that when piperazine is used as the polyamine monomer for preparing polyamide nanofiltration membrane, the prepared polyamide nanofiltration membrane not only has good permeability, but also has a higher sodium sulfate retention rate and a smaller pore size compared with other polyamine monomers, achieving unexpected technical effects.

[0141] The foregoing examples are merely illustrative and are used to explain some features of the method of the present invention. The appended claims are intended to require the widest possible range that can be imagined, and the embodiments presented herein are demonstrated by the applicant's actual test results. Therefore, the applicant's intention is that the appended claims are not limited by the selection of examples that illustrate the features of the present invention. Some numerical ranges used in the claims also include sub-ranges therein, and changes in these ranges should also be interpreted as being covered by the appended claims where possible.

Claims

1. A method for preparing an amino acid-regulated polyamide nanofiltration membrane, characterized in that: The following steps are involved: S1. The base film is mixed with the aqueous solution, allowed to stand, and the aqueous solution is removed and then dried; S2. The base film after removing the aqueous phase solution in step S1 is mixed with the organic phase solution, allowed to stand, the organic phase solution is removed, and the polyamide nanofiltration membrane is obtained by heating; The aqueous phase solution is a mixed solution of amino acids, piperazine and water; The organic phase solution is a mixed solution of polyacyl chloride and an organic solvent; The amino acids are lysine, cysteine, and glutamic acid; When the amino acid is lysine, the mass volume ratio of the amino acid to water is (5-10): 1 g / L; the mass volume ratio of piperazine to water is (2-4): 1 g / L; When the amino acid is cysteine, the mass volume ratio of the amino acid to deionized water is (3-5): 1 g / L; the mass volume ratio of piperazine to water is (2-4): 1 g / L; When the amino acid is glutamic acid, the mass volume ratio of the amino acid to deionized water is (3-10): 1 g / L; the mass volume ratio of piperazine to water is (2-4): 1 g / L; The polyacyl chloride is selected from one or more of 1,3,5-trimethylbenzene dicarboxylic acid chloride, terephthaloyl chloride or isophthaloyl chloride; The mass volume ratio of the polyacid chloride and the organic solvent is (1-2): 1 g / L.

2. The preparation method according to claim 1, characterized in that: The base film is polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile, polyethylene, polyvinyl chloride or polytetrafluoroethylene.

3. The preparation method according to claim 1, characterized in that: The organic solvent is selected from one or more of n-hexane, n-decane, petroleum ether, n-heptane and cyclohexane.

4. The preparation method according to claim 1, characterized in that: In the step S1, the standing time is 1 to 10 minutes; in the step S2, the standing time is 0.5 to 3 minutes.

5. The polyamide nanofiltration membrane prepared by the preparation method according to any one of claims 1 to 4.

6. Use of the polyamide nanofiltration membrane according to claim 5 in seawater desalination, divalent salt / monovalent salt separation in high-salt wastewater, wastewater volume reduction and / or water resource recovery.

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