A polyamide film resistant to acid and alkali cleaning and its preparation method

Abstract

This invention discloses an acid and alkali resistant polyamide membrane and its preparation method. The method is as follows: S1: Immerse the ultrafiltration base membrane in an aqueous sodium hydroxide solution for soaking and then set aside; S2: Treat the base membrane with a mixed aqueous solution of polyamine and aziridine crosslinking agent; S3: Wet the base membrane in an organic phase solution of polyacrylamide monomer to obtain a polyamide composite membrane; S4: Immerse the prepared polyamide composite membrane in an alcoholic solution of hydroxymethyl crosslinking agent, then dry it in a forced-air drying oven, and after washing with water, obtain the acid and alkali resistant polyamide membrane. This application uses two crosslinking agents, aziridine and hydroxymethyl, which can undergo specific crosslinking reactions with the carboxyl groups inside the polyamide membrane, to directly perform dual crosslinking modification on the membrane interior and surface, without introducing other polymer materials to avoid excessive increase in membrane permeation resistance. The polyamide membrane prepared by this method has both good acid and alkali resistance and water permeability.

Description

Technical Field

[0001] This invention belongs to the field of polyamide film preparation technology, specifically relating to an acid and alkali resistant polyamide film and its preparation method. Background Technology

[0002] Reverse osmosis (RO) membrane technology is considered one of the most effective water treatment technologies. Compared with traditional chemical water treatment technologies such as "flocculation-sedimentation," RO membrane technology has advantages such as simple operation, low operating cost, high ion removal rate (up to 97%), and low secondary pollution. However, during the operation of thermal power generating units, the circulating water continuously concentrates due to water evaporation and wind loss, increasing the salt content in the water. Carbonates exceed their solubility product, and the most unstable Ca(HCO3)2 and Mg(HCO3)2 are easily decomposed by heat to form carbonates that adhere to the membrane surface. Furthermore, the release of CO2 during the aeration process in the cooling tower exacerbates carbonate scaling. In addition, residual organosilicon substances in the water also gradually form scale. These scale deposits accumulate on the surface of heat exchangers and reverse osmosis membranes, affecting the operational safety of the unit and the water treatment efficiency of the reverse osmosis membrane. The suitable temperature and oxygen-rich conditions in the circulating water are ideal for microbial growth and reproduction; if not controlled effectively and promptly, this will rapidly lead to membrane fouling and corrosion.

[0003] Therefore, addressing scale buildup on membrane surfaces is a crucial issue for membranes used in power plant water treatment. Most power plants primarily employ acid and alkali rinsing to redissolve inorganic and organic scale. While this achieves scale removal, the acid and alkali cleaning solutions simultaneously cause hydrolysis of the reverse osmosis membrane's functional layer, leading to amide bond breakage. This damage to membrane integrity results in a significant decrease in separation performance and lifespan, increasing water treatment process costs. Therefore, developing a long-lasting, stable polyamide membrane material that combines high separation performance with resistance to acid and alkali cleaning is of great importance. Summary of the Invention

[0004] This application aims to overcome the problem of insufficient resistance to chemical cleaning by acids and alkalis in polyamide membranes, and provides an acid and alkali resistant polyamide membrane suitable for circulating cooling water treatment and its preparation method.

[0005] The technical solution adopted to achieve the purpose of this invention is as follows:

[0006] A method for preparing an acid and alkali resistant polyamide film includes the following processes:

[0007] 1) A flat-sheet ultrafiltration membrane (molecular weight cutoff ≈ 40,000-80,000 Da) is used as the base membrane. The ultrafiltration base membrane is immersed in a cleaning solution (sodium hydroxide aqueous solution with pH = 10-12) for 12 hours to remove residual organic solvents and acids from the base membrane. It is then rinsed thoroughly with pure water and ready for use. The ultrafiltration membrane can be one of polyacrylonitrile, polypropylene, polysulfone, polyethersulfone, or polyvinylidene fluoride.

[0008] 2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 1-4% (mass concentration) of polyamine and 0.1-1% (mass concentration) of aziridine crosslinking agent for 1-5 minutes. Then remove it and hang it vertically in the air for 1-10 minutes until there is no excess solution on the membrane surface. The polyamine can be selected from m-phenylenediamine, p-phenylenediamine, 2,7-diaminonaphthalene, 1,5-diaminonaphthalene, or 2,2'-diaminobiphenyl. The aziridine crosslinking agent can be selected from trimethylolpropane tris(3-aziridine propionate), trimethylolpropane-tris(3-(2-methylaziridine)propionate), 1-hydroxyethylaziridine, 2-(aziridine-1-yl)ethanol, or aziridine carboxylic acid methyl ester.

[0009] 3) Immerse the base membrane again in a 0.1-1% (mass concentration) organic phase solution of polyacrylamide chloride monomers and keep it for 1-10 minutes. Then, remove the membrane from the organic phase reaction solution and rinse the membrane surface with the corresponding pure organic phase solvent to obtain a polyamide composite membrane. The polyacrylamide chloride monomer can be one or a mixture of pyromellitic trimethylolpropionate chloride, isophthaloyl chloride, terephthaloyl chloride, succinic acid chloride, and biphenyl diacetyl chloride. The organic phase solvent is one or a mixture of hexane, cyclohexane, heptane, and octane.

[0010] 4) Immerse the prepared polyamide composite membrane in an alcohol solution containing 0.5-2% (mass concentration) of hydroxymethyl crosslinking agent for 1-4 minutes. Finally, place the membrane in a forced-air drying oven at 60-120℃ for 10-30 minutes. After washing with water, an acid and alkali resistant polyamide membrane is obtained. The hydroxymethyl crosslinking agent can be phenolic resin or trimethylol melamine, and the alcohol solvent can be one of ethanol, propanol, isopropanol, or n-butanol.

[0011] Preferably, the molecular weight cutoff of the ultrafiltration membrane in step 1) above is 50,000-60,000 Da;

[0012] Preferably, in step 2) above, the mass concentration of the polyamine is 2-3%, and the mass concentration of the aziridine crosslinking agent is 0.3-0.8%.

[0013] Preferably, the immersion time of the base film in the aqueous solution in step 2) above is 2-4 minutes;

[0014] Preferably, the base film in step 2) above is dried in air for 3-6 minutes;

[0015] Preferably, in step 3) above, the mass concentration of the polyacrylamide chloride monomer is 0.2%-0.5%;

[0016] Preferably, in step 3), the immersion time of the base film in the organic phase reaction solution is 2-5 minutes;

[0017] Preferably, the mass concentration of the hydroxymethyl crosslinking agent in step 4) above is 1-1.5%;

[0018] Preferably, in step 4) the composite membrane is immersed in the alcohol solution for 2-3 minutes.

[0019] Preferably, in step 4) above, the oven temperature is 80-100℃ and the heat treatment time is 15-20 minutes.

[0020] In this application, addressing the problem of existing polyamide membrane materials being easily hydrolyzed and damaged in long-term acid and alkaline chemical cleaning environments, a dual crosslinking modification treatment is applied to both the interior and surface of the polyamide membrane. First, an aziridine compound is added to the polyamide membrane polymerization reaction system. Utilizing the principle that aziridine groups can react rapidly with carboxyl groups, the residual carboxyl groups inside the polyamide membrane are crosslinked, thereby increasing the degree of crosslinking within the membrane. Then, the surface of the polyamide membrane is further treated with an alcohol solution of a hydroxymethyl crosslinking agent. Through the dehydration condensation reaction between hydroxymethyl and carboxyl groups, the surface density of the polyamide membrane is further increased, ultimately enhancing the polyamide membrane's resistance to acid and alkaline cleaning solutions.

[0021] Compared with existing methods for preparing washable polyamide membranes (such as CN202210924166.7) and other methods for improving the degree of crosslinking on the membrane surface (such as CN202111489504.0, CN202022685031.9), this application uses two crosslinking agents, aziridine and hydroxymethyl, which can undergo specific crosslinking reactions with the carboxyl groups inside the polyamide membrane. This directly performs dual crosslinking modification on both the interior and surface of the membrane, without introducing other polymer materials to avoid excessive increase in membrane permeation resistance. The polyamide membrane prepared by this method has both good resistance to acid and alkali cleaning and good water permeability.

[0022] As an explanation, the aqueous reaction solution in this application uses aziridine crosslinking agent because the reaction between aziridine groups and carboxyl groups has high activity in an alkaline environment, and the polyamine monomer in the aqueous phase can act as a catalyst to improve the crosslinking efficiency within the membrane. The post-treatment solution uses hydroxymethyl crosslinking agent because the hydroxymethyl compound in this application has low solubility and low reactivity in aqueous solution, which is not conducive to its direct addition to the aqueous reaction solution. Therefore, an alcohol is required as a solvent to prepare the post-treatment reaction solution. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0024] To evaluate the effectiveness of the method, this application also prepared three polyamide films as comparative examples, and the specific preparation process is described in the comparative examples below.

[0025] The test methods for the flux and desalination rate of the polyamide membrane described in this invention are as follows:

[0026] Membrane separation performance test: The prepared membrane was pre-pressed at 1.55 MPa with an electrolyte solution of 0.2% NaCl for half an hour to test the desalination performance and water flux of the polyamide membrane.

[0027] The formula for calculating water flux is shown in (1):

[0028] (1)

[0029] Where A – effective membrane area, m 2 t – Time required to collect Q volume of product, h; Q – Volume of product collected within time t, L.

[0030] The method for calculating the desalination performance of the membrane is shown in (2):

[0031] (2)

[0032] Where R is the desalination rate, and C is the salt content. f - Conductivity of the original solution, μS / cm; C p - Conductivity of the produced water, μS / cm.

[0033] Acid-alkali cleaning resistance test: The polyamide membrane was first immersed in an acidic cleaning solution (pH=2, prepared with hydrochloric acid) for 6 hours, then rinsed with pure water. Next, it was immersed in an alkaline cleaning solution (pH=11, prepared with sodium hydroxide) for another 6 hours, and rinsed with pure water. This "acid-alkali" cycle was repeated 20 times. The changes in membrane performance after the above cyclic cleaning treatment were examined to evaluate the acid and alkali cleaning resistance of the polyamide separation layer. Example 1

[0034] (1) A polyacrylonitrile flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 40000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues in the base membrane. Then it was rinsed with pure water and set aside for use.

[0035] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 1% (mass concentration) m-phenylenediamine and 0.1% (mass concentration) trimethylolpropane tris(3-acrylidylpropionate) for 1 minute. Then remove it and hang it vertically in the air for 1 minute until there is no excess solution on the membrane surface.

[0036] (3) Immerse the base film again in a 0.1% (mass concentration) solution of trimesoyl chloride and keep it for 1 minute. Then remove the film from the hexane reaction solution and rinse the film surface with hexane solvent to obtain a polyamide composite film.

[0037] (4) Immerse the prepared polyamide composite film in an ethanol solution containing 0.5% (mass concentration) phenolic resin for 1 minute, and finally put the film in a 60°C forced-air drying oven for 10 minutes. After washing with water, obtain an acid and alkali resistant polyamide film.

[0038] Performance testing: The initial polyamide membrane achieved a desalination rate of 97.2% and a water flux of 35.7 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 96.5% and a water flux of 37.1 L / m³. 2 .h Example 2

[0039] (1) A polypropylene flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 50000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues remaining in the base membrane. Then it was rinsed with pure water and set aside for use.

[0040] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 2% (mass concentration) p-phenylenediamine and 0.3% (mass concentration) trimethylolpropane-tris(3-(2-methylacrylidinyl)propionate, keep it for 2 minutes, then remove it and hang it vertically in the air for 3 minutes until there is no excess solution on the membrane surface.

[0041] (3) Immerse the base film again in a 0.2% (mass concentration) cyclohexane solution of isophthaloyl chloride and keep it for 2 minutes. Then remove the film from the cyclohexane reaction solution and rinse the film surface with cyclohexane solvent to obtain a polyamide composite film.

[0042] (4) Immerse the prepared polyamide composite film in a propanol solution containing 1% (mass concentration) phenolic resin for 2 minutes, and finally put the film in an 80°C drying oven for 15 minutes. After washing with water, obtain an acid and alkali resistant polyamide film.

[0043] Performance testing: The initial polyamide membrane achieved a desalination rate of 96.9% and a water flux of 37.0 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 96.6% and a water flux of 42.3 L / m³. 2 .h Example 3

[0044] (1) A polysulfone flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 60000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues remaining in the base membrane. Then it was rinsed with pure water and set aside for use.

[0045] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 3% (mass concentration) of 2,7-diaminonaphthalene and 0.8% (mass concentration) of 1-hydroxyethylaziridine for 4 minutes. Then remove it and hang it vertically in the air for 6 minutes until there is no excess solution on the membrane surface.

[0046] (3) Immerse the base film again in a 0.5% (mass concentration) heptane solution of terephthaloyl chloride and keep it for 5 minutes. Then remove the film from the heptane reaction solution and rinse the film surface with heptane solvent to obtain a polyamide composite film.

[0047] (4) Immerse the prepared polyamide composite film in an isopropanol solution containing 1.5% (mass concentration) phenolic resin for 3 minutes, and finally put the film in a 100°C forced-air drying oven for 20 minutes. After washing with water, obtain an acid and alkali resistant polyamide film.

[0048] Performance testing: The initial polyamide membrane achieved a desalination rate of 97.5% and a water flux of 42.4 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 96.7% and a water flux of 47.6 L / m³. 2 .h Example 4

[0049] (1) A polyethersulfone flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 80000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues in the base membrane. Then it was rinsed with pure water and set aside for use.

[0050] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 4% (mass concentration) 1,5-diaminonaphthalene and 1% (mass concentration) 2-(aziridin-1-yl)ethanol for 5 minutes. Then remove it and hang it vertically in the air for 10 minutes until there is no excess solution on the membrane surface.

[0051] (3) Immerse the base film again in a 1% (mass concentration) octane solution of succinyl chloride and keep it for 10 minutes. Then remove the film from the octane reaction solution and rinse the film surface with octane solvent to obtain a polyamide composite film.

[0052] (4) Immerse the prepared polyamide composite film in a n-butanol solution containing 2% (mass concentration) phenolic resin for 4 minutes, and finally put the film in a 120°C forced-air drying oven for 30 minutes. After washing with water, obtain an acid and alkali resistant polyamide film.

[0053] Performance testing: The initial polyamide membrane achieved a desalination rate of 96.9% and a water flux of 31.6 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 96.2% and a water flux of 37.3 L / m³. 2 .h Example 5

[0054] (1) A polyvinylidene fluoride flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 40000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues in the base membrane. Then it was rinsed with pure water and set aside for use.

[0055] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 1% (mass concentration) of 2,2'-diaminobiphenyl and 0.1% (mass concentration) of methyl aziridine carboxylate for 1 minute. Then remove it and hang it vertically in the air for 1 minute until there is no excess solution on the membrane surface.

[0056] (3) Immerse the base membrane again in a 0.1% (mass concentration) biphenyl diacetyl chloride solution and keep it for 1-10, 2-5 minutes. Then remove the membrane from the hexane reaction solution and rinse the membrane surface with hexane solvent to obtain a polyamide composite membrane.

[0057] (4) Immerse the prepared polyamide composite membrane in an ethanol solution containing 0.5% (mass concentration) of trimethylol melamine for 1 minute, and finally put the membrane in a 60°C drying oven for 10 minutes. After washing with water, obtain an acid and alkali resistant polyamide membrane.

[0058] Performance testing: The initial polyamide membrane achieved a desalination rate of 98.5% and a water flux of 42.3 L / m³. 2 The polyamide membrane, after undergoing acid-base cycle cleaning, achieved a desalination rate of 97.7% and a water flux of 48.7 L / m³. 2 .h Example 6

[0059] (1) A polyacrylonitrile flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 50000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues in the base membrane. Then it was rinsed with pure water and set aside for use.

[0060] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 2% (mass concentration) m-phenylenediamine and 0.3% (mass concentration) trimethylolpropane tris(3-acrylidylpropionate) for 2 minutes. Then remove it and hang it vertically in the air for 3 minutes until there is no excess solution on the membrane surface.

[0061] (3) Immerse the base film again in a 0.2% (mass concentration) cyclohexane pyromellitic chloride solution and keep it for 2 minutes. Then remove the film from the cyclohexane reaction solution and rinse the film surface with cyclohexane solvent to obtain a polyamide composite film.

[0062] (4) Immerse the prepared polyamide composite membrane in an ethanol solution containing 1% (mass concentration) of trimethylol melamine for 2 minutes, and finally put the membrane in an 80°C drying oven for 15 minutes. After washing with water, obtain an acid and alkali resistant polyamide membrane.

[0063] Performance testing: The initial polyamide membrane achieved a desalination rate of 97.1% and a water flux of 33.9 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 96.2% and a water flux of 43.1 L / m³. 2 .h Example 7

[0064] (1) A polysulfone flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 60000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues remaining in the base membrane. Then it was rinsed with pure water and set aside for use.

[0065] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 3% (mass concentration) p-phenylenediamine and 0.8% (mass concentration) trimethylolpropane-tris(3-(2-methylacrylidinyl)propionate, keep it for 4 minutes, then remove it and hang it vertically in the air for 6 minutes until there is no excess solution on the membrane surface.

[0066] (3) Immerse the base film again in a 0.5% (mass concentration) octane solution of isophthaloyl chloride and keep it for 5 minutes. Then remove the film from the octane reaction solution and rinse the film surface with octane solvent to obtain a polyamide composite film.

[0067] (4) Immerse the prepared polyamide composite membrane in a propanol solution containing 1.5% (mass concentration) of trimethylol melamine for 3 minutes, and finally put the membrane in a 100°C drying oven for 20 minutes. After washing with water, obtain an acid and alkali resistant polyamide membrane.

[0068] Performance testing: The initial polyamide membrane achieved a desalination rate of 96.2% and a water flux of 39.7 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 95.3% and a water flux of 48.6 L / m³. 2 .h Example 8

[0069] (1) A polyethersulfone flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 80000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues in the base membrane. Then it was rinsed with pure water and set aside for use.

[0070] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 4% (mass concentration) of 2,7-diaminonaphthalene and 1% (mass concentration) of 1-hydroxyethylaziridine for 5 minutes. Then remove it and hang it vertically in the air for 10 minutes until there is no excess solution on the membrane surface.

[0071] (3) Immerse the base membrane again in a 1% (mass concentration) cyclohexane solution of succinyl chloride and keep it for 10 minutes. Then remove the membrane from the cyclohexane reaction solution and rinse the membrane surface with cyclohexane solvent to obtain a polyamide composite membrane.

[0072] (4) Immerse the prepared polyamide composite membrane in an ethanol solution containing 2% (mass concentration) trimethylol melamine for 4 minutes, and finally put the membrane in a 120°C drying oven for 30 minutes. After washing with water, obtain an acid and alkali resistant polyamide membrane.

[0073] Performance testing: The initial polyamide membrane achieved a desalination rate of 96.7% and a water flux of 44.0 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 95.9% and a water flux of 47.5 L / m³. 2 .h Example 9

[0074] (1) A polyvinylidene fluoride flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 60000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues in the base membrane. Then it was rinsed with pure water and set aside for use.

[0075] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 2% (mass concentration) 2,2'-diaminobiphenyl and 1% (mass concentration) methyl aziridine carboxylate for 2 minutes. Then remove it and hang it vertically in the air for 5 minutes until there is no excess solution on the membrane surface.

[0076] (3) Immerse the base membrane again in a 0.5% (mass concentration) heptane solution of biphenyl diacetyl chloride and keep it for 5 minutes. Then remove the membrane from the heptane reaction solution and rinse the membrane surface with heptane solvent to obtain a polyamide composite membrane.

[0077] (4) Immerse the prepared polyamide composite membrane in a butanol solution containing 1% (mass concentration) of trimethylol melamine for 2 minutes, and finally put the membrane in a 100°C drying oven for 20 minutes. After washing with water, obtain a polyamide membrane resistant to acid and alkali cleaning.

[0078] Performance testing: The initial polyamide membrane achieved a desalination rate of 98.1% and a water flux of 39.0 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 97.4% and a water flux of 46.0 L / m³. 2 .h Comparative Example 1

[0079] (1) A polysulfone flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 60000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues remaining in the base membrane. Then it was rinsed with pure water and set aside for use.

[0080] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in an aqueous solution containing 2% (mass concentration) m-phenylenediamine for 2 minutes. Then remove it and hang it vertically in the air for 5 minutes until there is no excess solution on the membrane surface.

[0081] (3) Immerse the base film again in a 0.1% (mass concentration) pyromellitic chloride solution and keep it for 5 minutes. Then remove the film from the n-hexane reaction solution and rinse the film surface with n-hexane solvent to obtain a polyamide composite film.

[0082] (4) Immerse the prepared polyamide composite film in n-butanol solution for 2 minutes, and finally put the film in a 100°C drying oven for 20 minutes. After washing with water, a wash-resistant polyamide film is obtained.

[0083] Performance testing: The initial polyamide membrane achieved a desalination rate of 99.2% and a water flux of 34.6 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 88.5% and a water flux of 72.0 L / m³. 2 .h Comparative Example 2

[0084] (1) A polysulfone flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 60000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues remaining in the base membrane. Then it was rinsed with pure water and set aside for use.

[0085] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in a mixed aqueous solution containing 2% (mass concentration) m-phenylenediamine and 1% (mass concentration) trimethylolpropane tris(3-acrylidylpropionate) for 2 minutes. Then remove it and hang it vertically in the air for 5 minutes until there is no excess solution on the membrane surface.

[0086] (3) Immerse the base film again in a 0.1% (mass concentration) pyromellitic chloride solution and keep it for 5 minutes. Then remove the film from the n-hexane reaction solution and rinse the film surface with n-hexane solvent to obtain a polyamide composite film.

[0087] (4) Immerse the prepared polyamide composite film in n-butanol solution for 2 minutes, and finally put the film in a 100°C drying oven for 20 minutes. After washing with water, a wash-resistant polyamide film is obtained.

[0088] Performance testing: The initial polyamide membrane achieved a desalination rate of 97.4% and a water flux of 44.9 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 94.0% and a water flux of 49.3 L / m³. 2 .h Comparative Example 3

[0089] (1) A polysulfone flat sheet ultrafiltration membrane (molecular weight cutoff ≈ 60000 Da) was used as the base membrane. The ultrafiltration membrane was immersed in a cleaning solution (sodium hydroxide aqueous solution with pH=12) for 12 hours to clean the organic solvent and acid residues remaining in the base membrane. Then it was rinsed with pure water and set aside for use.

[0090] (2) Remove the ultrafiltration membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Immerse the membrane in an aqueous solution containing 2% (mass concentration) m-phenylenediamine for 2 minutes. Then remove it and hang it vertically in the air for 5 minutes until there is no excess solution on the membrane surface.

[0091] (3) Immerse the base film again in a 0.1% (mass concentration) pyromellitic chloride solution and keep it for 5 minutes. Then remove the film from the n-hexane reaction solution and rinse the film surface with n-hexane solvent to obtain a polyamide composite film.

[0092] (4) Immerse the prepared polyamide composite film in a n-butanol solution containing 1% (mass concentration) phenolic resin for 2 minutes, and finally put the film in a 100°C forced-air drying oven for 20 minutes. After washing with water, a wash-resistant polyamide film is obtained.

[0093] Performance testing: The initial polyamide membrane achieved a desalination rate of 98.7% and a water flux of 35.4 L / m³. 2 The polyamide membrane, after undergoing acid-alkali cycle cleaning, achieved a desalination rate of 94.6% and a water flux of 52.4 L / m³. 2 .h

[0094] Table 1. Differences in membrane performance and stability between the examples and comparative examples.

[0095]

[0096] As shown in Table 1, the desalination rate of the unmodified polyamide membrane (Comparative Example 1) decreased from 99.2% to 88.5% after 20 cycles of acid and alkali cleaning. However, after crosslinking treatment with either aziridine or hydroxymethyl crosslinking agent (Comparative Examples 2 and 3), the decrease in desalination rate was significantly improved, demonstrating that crosslinking treatment enhances the acid and alkali resistance of the polyamide membrane. After crosslinking with both crosslinking agents (Examples 1-9), the change in desalination rate before and after acid and alkali treatment was basically <1%, further demonstrating that the method described in this application can be used to prepare a long-life, acid and alkali resistant polyamide membrane suitable for power plant cooling water treatment.

[0097] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing an acid and alkali resistant polyamide film, characterized in that, The process includes the following steps: S1: A flat sheet ultrafiltration membrane is used as the base membrane. The base membrane is immersed in an aqueous sodium hydroxide solution to clean the organic solvents and acids remaining in the base membrane. Then it is rinsed with pure water and set aside for use. S2: Remove the base membrane from the pure water and rinse the membrane surface with pure nitrogen to remove excess water. Then immerse the base membrane in a mixed aqueous solution of polyamine and aziridine crosslinking agent for a period of time. After that, remove it and hang it vertically in the air until there is no excess solution on the surface of the base membrane. S3: Immerse the base membrane again in the organic phase solution of polyacryl chloride monomers, keep it for a period of time, then remove it and rinse the membrane surface with the corresponding pure organic phase solvent to obtain a polyamide composite membrane; S4: Immerse the prepared polyamide composite film in an alcohol solution containing 0.5-2% by mass of hydroxymethyl crosslinking agent, keep it for a period of time, and finally put the composite film into a forced-air drying oven to dry. After washing with water, an acid and alkali resistant polyamide film is obtained. The aziridine crosslinking agent is one of trimethylolpropane tris(3-aziridine propionate), trimethylolpropane-tris(3-(2-methylaziridine)propionate), 1-hydroxyethylaziridine, 2-(aziridine-1-yl)ethanol, and aziridine carboxylic acid methyl ester.

2. The method for preparing an acid and alkali resistant polyamide film according to claim 1, characterized in that, In step S1, the ultrafiltration membrane is made of one of the following materials: polyacrylonitrile, polypropylene, polysulfone, polyethersulfone, and polyvinylidene fluoride; the ultrafiltration membrane has a molecular weight cutoff of 40,000-80,000 Da; and the pH of the sodium hydroxide aqueous solution in step S1 is 10-12.

3. The method for preparing an acid and alkali resistant polyamide film according to claim 1, characterized in that, In step S2, the polyamine is one of m-phenylenediamine, p-phenylenediamine, 2,7-diaminonaphthalene, 1,5-diaminonaphthalene, or 2,2'-diaminobiphenyl.

4. The method for preparing an acid and alkali resistant polyamide film according to claim 1, characterized in that, In step S3, the polyacrylamide chloride monomer is one or a mixture of pyromellitic trimethylolpropionate chloride, isophthaloyl chloride, terephthaloyl chloride, succinicoyl chloride, and biphenyl diacetyl chloride; the organic phase solvent is one or a mixture of hexane, cyclohexane, heptane, and octane.

5. The method for preparing an acid and alkali resistant polyamide film according to claim 1, characterized in that, In step S4, the hydroxymethyl crosslinking agent is phenolic resin or trimethylol melamine, and the alcohol solvent is one of ethanol, propanol, isopropanol, and n-butanol.

6. The method for preparing an acid and alkali resistant polyamide film according to claim 1, characterized in that, In step S2, the mass concentration of the polyamine is 1-4%; the mass concentration of the aziridine crosslinking agent is 0.1-1%; the immersion time of the base film in the aqueous solution is 2-4 minutes; and the drying time of the base film in air is 3-6 minutes.

7. The method for preparing an acid and alkali resistant polyamide film according to claim 1, characterized in that, In step S3, the mass concentration of the polyacrylamide chloride monomer is 0.1-1%; the immersion time of the base film in the organic phase reaction solution is 2-5 minutes.

8. The method for preparing an acid and alkali resistant polyamide film according to claim 1, characterized in that, In step S4, the composite membrane is immersed in the alcohol solution for 2-3 minutes; the temperature of the forced-air drying oven is 60-120℃, and the heat treatment time is 10-30 minutes.

9. The method for preparing an acid and alkali resistant polyamide film according to claim 1, characterized in that, In step S2, the base film is immersed in a mixed aqueous solution of polyamine and aziridine crosslinking agent for 1-5 minutes, and is vertically suspended in air for 1-10 minutes; in step S3, the base film is immersed in an organic phase solution of polyacrylamide chloride monomer for 1-10 minutes; in step S4, the polyamide composite film is immersed in an alcohol solution containing 0.1-1% by mass of hydroxymethyl crosslinking agent for 1-4 minutes.

10. A polyamide film resistant to acid and alkali cleaning, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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