Anti-fouling reverse osmosis membrane and method for preparing the same

Abstract

The application relates to the technical field of reverse osmosis membranes, and particularly discloses an anti-pollution reverse osmosis membrane and a preparation method thereof, which comprises the following steps: preparing a polyamide layer on a base membrane by using organic amine and organic acyl chloride to perform an interfacial polymerization reaction; reacting a photoinitiator containing amino groups or phenolic hydroxyl groups with acyl chloride groups remaining in the interfacially polymerized polyamide layer to introduce the photoinitiator into the membrane surface; uniformly pouring an amphoteric ion solution on the membrane surface and irradiating under ultraviolet light to initiate a polymerization reaction; and heat-treating the membrane in an oven to obtain the anti-pollution reverse osmosis membrane. The application utilizes a photoinitiated radical polymerization strategy to efficiently graft amphoteric ion polymers on the membrane surface, compared with a traditional grafting method, the operation process is simple, the grafting rate is fast (within 5 minutes), the use of organic solvents is reduced, the prepared reverse osmosis membrane has excellent anti-pollution performance, and has great industrial application potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of reverse osmosis membranes, and particularly relates to an anti-fouling reverse osmosis membrane and a preparation method thereof. BACKGROUND

[0002] Polyamide reverse osmosis membranes play an important role in the fields of seawater desalination, brackish water treatment, industrial wastewater treatment and drinking water production due to their good separation performance, chemical stability and high separation precision. However, membrane fouling often occurs during the separation process, which leads to problems such as reduced separation efficiency, deteriorated membrane performance, shortened service life and increased energy consumption, which become a bottleneck restricting further promotion.

[0003] Studies have shown that the water quality, operating conditions and membrane surface characteristics have an important influence on membrane fouling. At present, in order to alleviate membrane fouling, various solutions have been developed, such as feed liquid pretreatment, improved operating conditions, membrane chemical cleaning and the like. However, the above measures will increase the operating cost and cause irreversible membrane damage. Therefore, the development of anti-fouling reverse osmosis membranes can fundamentally alleviate the problem of membrane fouling and overcome the bottleneck of industrial application.

[0004] Membrane fouling is mainly related to the interface interaction between the pollutants and the membrane surface. The membrane surface characteristics, such as hydrophilicity, roughness and charge density, have an important influence on the interaction between the pollutants and the membrane. Among them, the membrane surface hydrophilicity plays a leading role in improving the anti-fouling performance of the membrane. Most of the pollutants are hydrophobic, and the more hydrophobic the membrane surface is, the easier it is for the pollutants to approach the membrane due to the existence of hydrophobic interaction force, and the pollutants are more likely to be adsorbed or deposited on the membrane surface, resulting in membrane fouling. The membrane with strong hydrophilicity is beneficial to the formation of a hydration layer on the membrane surface, which blocks the direct contact between the pollutants and the membrane surface, and also reduces the adsorption of hydrophobic pollutants, greatly reducing the membrane fouling trend. The zwitterions contain both cation and anion pairs, which can combine multiple water molecules through electrostatic interaction to form a thicker and more stable hydration layer, which can effectively prevent the adsorption of pollutants and improve the anti-fouling performance of the membrane.

[0005] Currently, the main method to introduce zwitterions on the membrane surface is surface grafting. Surface grafting is connected by covalent bond, which has no problem of firmness. Surface grafting can be divided into grafting to the main chain method and grafting from the main chain method. The former is mainly through the residual acyl chloride on the membrane surface or the introduction of reaction sites by pre-reaction to graft the target polymer onto the membrane surface. The method is simple, but due to the limited number of active functional groups on the membrane surface and the spatial exclusion of pre-grafted polymer materials, it leads to uneven grafting and low coverage. The commonly used methods for grafting from the main chain method are reversible addition-fragmentation chain transfer polymerization strategy and atom transfer radical polymerization strategy. The biggest advantage is that the reaction is controllable, which can accurately control the composition, length and structure of the grafted polymer. However, the reaction process of the reversible addition-fragmentation chain transfer polymerization strategy and the atom transfer radical polymerization strategy is complex and time-consuming, and the reaction conditions are harsh, which is difficult to apply to the continuous production process of polyamide reverse osmosis membranes, and is not conducive to industrial scale-up. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a preparation method of anti-fouling reverse osmosis membrane, which uses a simple and efficient photo-initiated free radical polymerization strategy to graft zwitterionic polymers on the membrane surface, enhances the hydrophilicity of the reverse osmosis membrane surface, builds a stable hydration layer on the membrane surface, and improves the anti-fouling performance of the existing reverse osmosis membrane. The technical scheme adopted by the present application is as follows:

[0007] A preparation method of anti-fouling reverse osmosis membrane, comprising the following steps:

[0008] (1) fixing the base membrane on the plate frame, coating the organic amine aqueous monomer solution on the surface of the base membrane and standing, then pouring out the excess aqueous solution, and blowing the residual aqueous solution on the surface of the base membrane with an air knife;

[0009] (2) pouring the organic acid chloride oil phase solution onto the membrane surface obtained in step (1), and performing interfacial polymerization reaction to form a cross-linked polyamide separation layer, pouring off the residual oil phase solution, and washing the unreacted organic acid chloride monomer with an organic solvent;

[0010] (3) reacting the photo-initiator solution with the residual acyl chloride on the membrane surface prepared in step (2), then pouring off the excess photo-initiator solution and blowing the water droplets on the surface with an air knife;

[0011] (4) pouring the zwitterion aqueous solution onto the membrane surface obtained in step (3), and irradiating the zwitterionic polymer under ultraviolet light, then pouring off the excess zwitterionic aqueous solution and washing the membrane surface with deionized water;

[0012] (5) heat treating the membrane obtained in step (4) in an oven to obtain an anti-fouling polyamide reverse osmosis membrane.

[0013] Preferably, in the step (1), the organic amine aqueous phase monomer is m-phenylenediamine, and the standing time is 3-5 min; wherein the mass concentration of m-phenylenediamine used is 0.1-10%.

[0014] Preferably, in the step (1), the bottom membrane is one of polysulfone ultrafiltration membrane, polyethersulfone ultrafiltration membrane, polyimide ultrafiltration membrane, polyacrylonitrile ultrafiltration membrane, polyethylene ultrafiltration membrane or polypropylene ultrafiltration membrane.

[0015] Preferably, in the step (2), the organic acyl chloride is at least one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, mellitic acid chloride, glutaroyl chloride and fumaroyl; the organic solvent is at least one of n-hexane, cyclohexane, n-heptane, toluene, Isopar-G, Isopar-E, Isopar-H, Isopar-L and Isopar-M; and the concentration mass concentration of the organic acyl chloride oil phase solution is 0.01-2%.

[0016] Preferably, in the step (2), the polymerization reaction time is 10-300 s.

[0017] Preferably, in the step (3), the photoinitiator is at least one of benzophenone, 4-hydroxybenzophenone, 4-aminobenzophenone, 4,4-dihydroxybenzophenone and 4,4-diaminobenzophenone; wherein the mass concentration of the photoinitiator used is 0.1-10%.

[0018] Preferably, in the step (3), the reaction time of the photoinitiator and the acyl chloride is 10-150 s.

[0019] Preferably, in the step (4), the zwitterion is at least one of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, methacryloyloxyethyl trimethyl ammonium chloride, 2-methacryloyloxyethylphosphocholine and 3-((3-acrylamidopropyl)dimethylammonio)propanoate; wherein the mass concentration of the zwitterion used is 0.1-5%.

[0020] Preferably, in the step (4), the grafting time is 10-150 s.

[0021] Preferably, in the step (4), the heat treatment temperature is 50-90℃, and the heat treatment time is 30-300 s.

[0022] An anti-pollution reverse osmosis membrane prepared by the preparation method of the anti-pollution reverse osmosis membrane.

[0023] The principle of the present application is that the benzophenone active monomer as a photoinitiator can reduce H to form a carbon-hydrogen free radical in the polymer under ultraviolet irradiation, the carbon-hydrogen free radical can stably initiate free radical polymerization, and permanent chemical crosslinking is formed on the surface. 4,4-dihydroxybenzophenone or 4,4-diamino benzophenone can react with residual acyl chloride on the membrane surface to introduce it into the membrane surface as a photoinitiator, and then graft zwitterions containing double bonds under ultraviolet irradiation to realize the hydrophilic modification of the reverse osmosis membrane surface.

[0024] Compared with the prior art, the present application has the beneficial effects that:

[0025] (1) In the present application, the photoinitiator is introduced into the membrane surface by reacting the residual acyl chloride in the nascent polyamide layer with the photoinitiator containing phenolic hydroxyl or amino group, which is shorter in time required (within 5 minutes) compared with the traditional surface activation process, can be continuously carried out after the interfacial polymerization reaction, and is convenient for industrial production.

[0026] (2) In the present application, the zwitterionic polymer is grafted on the membrane surface by photoinitiated free radical polymerization, which is simple and efficient compared with the traditional grafting method, the reaction time is significantly shortened (within 10 minutes), batch production is easy, and the use of organic solvents in the reaction process is reduced.

[0027] (3) The anti-fouling reverse osmosis membrane grafted with zwitterionic polymer provided by the present application effectively improves the anti-fouling performance of the reverse osmosis membrane while ensuring the membrane flux and salt rejection. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 The preparation flow chart of the anti-fouling polyamide reverse osmosis membrane prepared in the present application;

[0029] Figure 2 The infrared spectrum and X-ray photoelectron spectrum of the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in Example 4 of the present application and the polyamide reverse osmosis membrane of Comparative Example 1;

[0030] Figure 3 The water contact angle and surface energy of the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in Example 4 of the present application and the polyamide reverse osmosis membrane of Comparative Example 1;

[0031] Figure 4 The NaCl separation performance of the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in Example 4 of the present application and the polyamide reverse osmosis membrane of Comparative Example 1;

[0032] Figure 5 The normalized flux and anti-fouling index of the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in Example 4 of the present application and the polyamide reverse osmosis membrane of Comparative Example 1 in the bovine serum albumin filtration process;

[0033] Figure 6 Normalized flux and anti-fouling index of the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in Example 4 of the present application and the polyamide reverse osmosis membrane of Comparative Example 1 during the filtration process of simulated gypsum solution. DETAILED DESCRIPTION

[0034] In order to make the advantages, technical solutions of the present application more clear and explicit, the present application will be described in detail below in combination with specific examples and drawings.

[0035] The raw materials required by the present application can be purchased through commercial channels.

[0036] The detection method of the permeation flux and salt rejection rate of the reverse osmosis membrane: the flux and salt rejection rate of the reverse osmosis membrane are tested by using a cross-flow performance evaluation device, and the test system includes a pump, a membrane cell, a pipeline, a regulating valve, a pressure and flow detector, etc., wherein the effective membrane area for testing is 18.2cm 2 , the test pressure is 15bar, and the test temperature is 25±0.5℃. The raw material liquid for testing the salt rejection rate is NaCl (2000ppm). Each membrane sample is pre-pressed for at least 2h before sampling test, so as to maintain a stable flux.

[0037] The calculation formula of the flux (P) is as follows:

[0038]

[0039] Wherein, P is the flux of the membrane (L·m -2 ·h -1 ·bar -1 ), V is the volume of water permeating through the membrane (L), s is the effective area of the membrane (m 2 ), t is the permeation time (h), and p is the test pressure (bar).

[0040] The calculation formula of the rejection rate (R) is as follows:

[0041]

[0042] Wherein, C p and C f are the salt concentrations of the permeate and the raw material liquid, respectively. The salt concentration is detected by a conductivity meter.

[0043] The detection method of the anti-fouling performance of the reverse osmosis membrane: the anti-fouling performance test of the reverse osmosis membrane is carried out by using the above cross-flow reverse osmosis device. During the experiment, the permeate and the concentrated liquid are continuously circulated to the feed tank. In the first stage, the membrane is pre-pressed with deionized water for 2 hours under the adjusted pressure, so as to obtain a stable pure water flux (J w0); In the second stage, the deionized water was replaced with the pollutant solution and filtered at the same pressure for 4 hours, and the stable flux (J p ); Finally, the fouled membrane was cleaned and the pure water flux (J w The above steps were repeated twice. The organic pollutants and inorganic pollutants used in the test were bovine serum albumin (100 ppm) and simulated gypsum solution (1000 ppm Na2SO4 and 1000 ppm CaCl2). t ), reversible flux decline rate (DR r ) and irreversible flux decline rate (DR ir ) is calculated using the following formula:

[0044]

[0045] Comparative Example 1

[0046] This comparative example 1 provides a method for preparing a reverse osmosis membrane, comprising the following steps:

[0047] (1) dissolving m-phenylenediamine in water to obtain an aqueous solution with a mass concentration of 5%;

[0048] (2) slowly pouring the aqueous solution prepared in step (1) onto the polysulfone ultrafiltration membrane and soaking it for 3 to 5 minutes, then pouring out the excess aqueous solution and drying the residual aqueous solution on the membrane surface with an air knife;

[0049] (3) dissolving trimesoyl chloride in n-hexane to obtain a trimesoyl chloride oil phase solution with a mass concentration of 0.1%;

[0050] (4) slowly pouring the oil phase solution obtained in step (3) onto the upper surface of the membrane obtained in step (2), interfacial polymerization for 150 seconds to form a cross-linked polyamide separation layer, pouring the residual trimesoyl chloride oil phase solution from the membrane surface, and washing the membrane surface with n-hexane;

[0051] (5) heat-treating the membrane obtained in step (4) in an oven at 70° C. for 3 min to obtain a polyamide reverse osmosis membrane;

[0052] The separation performance of the polyamide reverse osmosis membrane prepared by the above method was tested, and its water production flux was 2.3 L·m -2 ·h -1 bar -1 , NaCl rejection was 99.2%.

[0053] Example 1

[0054] like Figure 1As shown, the present embodiment 1 provides a method for preparing an anti-fouling reverse osmosis membrane, comprising the following steps:

[0055] (1) Fix the polysulfone base membrane on a plate frame, pour the 5% m-phenylenediamine aqueous solution on the surface of the base membrane and stand for 3-5 min, then pour off the excess aqueous solution and dry the residual aqueous solution on the surface of the base membrane with an air knife;

[0056] (2) Pour the 0.1% trimesoyl chloride oil phase solution on the surface of the membrane obtained in step (1), interfacial polymerize for 150 s to form a cross-linked polyamide separation layer, pour off the residual oil phase solution, and wash the unreacted organic acid chloride monomers with an organic solvent;

[0057] (3) Pour the 0.5%, 2%, 4%, 6%, 8% 4,4-dihydroxybenzophenone aqueous solution on the surface of the TFC membrane prepared in step (2) to react with the residual acid chloride for 120 s, then pour off the excess photoinitiator solution and blow off the water droplets on the surface with an air knife;

[0058] (4) Pour the 3.0% [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide aqueous solution on the surface of the membrane obtained in step (3) and irradiate under ultraviolet for 120 s to graft the zwitterionic polymer, then pour off the excess zwitterionic aqueous solution and wash the surface of the membrane with deionized water;

[0059] (5) Heat treat the membrane obtained in step (4) in a 70°C oven for 3 min to obtain a polyamide reverse osmosis composite membrane;

[0060] The anti-fouling polyamide reverse osmosis membrane prepared by the above method is subjected to separation performance test, and is respectively recorded as embodiment 1-1 to 1-5 according to the mass concentration of 4,4-dihydroxybenzophenone of 0.5%, 2%, 4%, 6%, 8%, and the test results are shown in Table 1:

[0061] Table 1: Separation performance test results of embodiment 1 and comparative example 1

[0062]

[0063] As shown in Table 1, the NaCl rejection of the reverse osmosis membrane after surface grafting is almost unchanged; with the increase of the concentration of 4,4-dihydroxybenzophenone, the flux first increases and then decreases, and the flux decrease is because the concentration of 4,4-dihydroxybenzophenone is too high, the number of hydrophobic benzene rings introduced on the membrane surface increases, the hydrophilicity of the membrane surface decreases, and the water transmission resistance increases. When the concentration of 4,4-dihydroxybenzophenone is 4%, the flux is 2.2 L·m -2 ·h -1 ·bar -1, NaCl rejection was 98.7%, which was no significant difference from the performance of Control Example 1.

[0064] Example 2

[0065] This embodiment 2 provides a method for preparing an anti-pollution polyamide reverse osmosis membrane with high efficiency photoinitiated polymerization and grafted zwitterions, comprising the following steps:

[0066] (1) Fix the base film on the plate frame, pour a 5% m-phenylenediamine aqueous solution on the surface of the base film and let it stand for 3 to 5 minutes, then pour out the excess aqueous solution and blow dry the residual aqueous solution on the surface of the base film with an air knife;

[0067] (2) pouring a 0.1% mass concentration of trimesoyl chloride oil phase solution onto the membrane surface obtained in step (1), interfacial polymerization for 150 seconds to form a cross-linked polyamide separation layer, pouring out the remaining oil phase solution, and washing the unreacted organic acid chloride monomer with an organic solvent;

[0068] (3) Pour a 4% mass concentration of 4,4-dihydroxybenzophenone aqueous solution on the surface of the TFC membrane prepared in step (2) and react with the residual acyl chloride for 30 seconds, 60 seconds, 90 seconds, 120 seconds, and 150 seconds, respectively, then pour out the excess photoinitiator solution and blow away the water droplets on the surface with an air knife;

[0069] (4) pouring a 3.0% (mass concentration) aqueous solution of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide onto the membrane surface obtained in step (3), and irradiating the membrane under ultraviolet light for 120 seconds to graft the zwitterionic polymer. Afterwards, the excess zwitterionic aqueous solution was discarded, and the membrane surface was rinsed with deionized water.

[0070] (5) heat-treating the membrane obtained in step (4) in an oven at 70° C. for 3 min to obtain a polyamide reverse osmosis composite membrane;

[0071] The anti-fouling polyamide reverse osmosis membrane prepared by the above method was tested for separation performance, and the reaction time of 4,4-dihydroxybenzophenone was 30s, 60s, 90s, 120s, and 150s, respectively, as Examples 2-1 to 2-5. The test results are shown in Table 2:

[0072] Table 2 Separation performance test results of Example 2 and Control Example 1

[0073]

[0074] From Table 2, it can be seen that the NaCl rejection of the reverse osmosis membrane after surface grafting has little change; with the increase of the reaction time of 4,4-dihydroxybenzophenone, the flux first increases and then decreases, and the decrease of the flux is because the reaction time of 4,4-dihydroxybenzophenone is too long, the number of hydrophobic benzene rings introduced on the membrane surface increases, the hydrophilicity of the membrane surface decreases, and the water transfer resistance increases. When the reaction time of 4,4-dihydroxybenzophenone is 120s, the flux is 2.3L·m -2 ·h -1 ·bar -1 , the NaCl rejection is 98.7%, and there is no obvious difference in performance compared with Example 1.

[0075] Example 3

[0076] The present Example 3 provides a preparation method of a high-efficiency light-induced polymerization grafting zwitterion anti-pollution polyamide reverse osmosis membrane, comprising the following steps:

[0077] (1) fixing the base membrane on a plate frame, pouring a 5% mass concentration m-phenylenediamine aqueous solution on the surface of the base membrane and standing for 3-5min, then pouring off the excess aqueous solution, and blowing off the residual aqueous solution on the surface of the base membrane with an air knife;

[0078] (2) pouring a 0.1% mass concentration trimesoyl chloride oil phase solution on the surface of the membrane obtained in step (1), interfacial polymerization for 150s to form a cross-linked polyamide separation layer, pouring off the residual oil phase solution, and washing the unreacted organic acid chloride monomers with an organic solvent;

[0079] (3) pouring a 4% mass concentration 4,4-dihydroxybenzophenone aqueous solution on the TFC membrane prepared in step (2) to react with the residual acid chloride for 120s, then pouring off the excess photoinitiator solution and blowing off the water droplets on the surface with an air knife;

[0080] (4) pouring a [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide aqueous solution with a mass concentration of 1.0%, 2.0%, 3.0%, 4.0% and 5.0% on the surface of the membrane obtained in step (3), and grafting zwitterion polymer under ultraviolet irradiation for 120s, respectively, then pouring off the excess zwitterion aqueous solution and washing the membrane surface with deionized water;

[0081] (5) heating the membrane obtained in step (4) in a 70°C oven for 3min to obtain a polyamide reverse osmosis composite membrane;

[0082] The anti-fouling polyamide reverse osmosis membrane prepared by the above method was tested for separation performance, and according to the mass concentration of [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide was 1.0%, 2.0%, 3.0%, 4.0%, 5.0% respectively, examples 3-1~3-5, the test results are shown in table 3:

[0083] Table 3 separation performance test results of example 3 and comparative example 1

[0084]

[0085] As can be seen from table 3, after surface grafting, the NaCl rejection of the reverse osmosis membrane almost does not change; with the increase of the mass concentration of [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide, the flux first increases and then decreases, and the flux decreases because the mass concentration of [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide is too high, and an extra coating is formed on the membrane surface, increasing the water transfer resistance. When the mass concentration of [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide is 3.0%, the flux is 2.2L·m -2 ·h -1 ·bar -1 , the NaCl rejection is 98.8%, and there is no obvious difference in performance compared with comparative example 1.

[0086] Example 4

[0087] The present embodiment 4 provides a preparation method of high-efficiency light-induced polymerization grafting zwitterion anti-fouling polyamide reverse osmosis membrane, comprising the following steps:

[0088] (1) fix the base membrane on the plate frame, pour the water phase solution of m-phenylenediamine with a mass concentration of 5% on the surface of the base membrane and stand for 3~5min, then pour away the excess water phase solution, and dry the residual water phase solution on the surface of the base membrane with air knife;

[0089] (2) pour the oil phase solution of trimesoyl chloride with a mass concentration of 0.1% on the surface of the membrane obtained in step (1), interfacial polymerization for 150s to form a cross-linked polyamide separation layer, pour away the residual oil phase solution, and wash the unreacted organic acid chloride monomer with organic solvent;

[0090] (3) pour the water solution of 4,4-dihydroxybenzophenone with a mass concentration of 4% on the surface of the TFC membrane prepared in step (2) to react with the residual acid chloride for 120s, then pour away the excess photoinitiator solution and blow off the water droplets on the surface with air knife;

[0091] (4) Pour the aqueous solution of [2-(methacryloyloxy)ethyl]dimethyl-(3- sulfopropyl)ammonium hydroxide with a mass concentration of 3% on the surface of the membrane obtained in step (3), and graft the zwitterionic polymer under ultraviolet irradiation for 30 s, 60 s, 90 s, 120 s, and 150 s, respectively, and then pour off the excess zwitterionic aqueous solution and rinse the surface of the membrane with deionized water;

[0092] (5) Heat treat the membrane obtained in step (4) in an oven at 70°C for 3 min to obtain a polyamide reverse osmosis composite membrane;

[0093] The anti-fouling polyamide reverse osmosis membrane prepared by the above method is subjected to separation performance testing, and is denoted as Examples 4-1 to 4-5 according to the grafting time of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide of 30 s, 60 s, 90 s, 120 s, and 150 s, respectively. The test results are shown in Table 4:

[0094] Table 4. Separation performance test results of Examples 4 and Comparative Example 1

[0095]

[0096] As shown in Table 4, the NaCl rejection of the reverse osmosis membrane after surface grafting has little change; with the increase of the grafting time of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, the flux first increases and then decreases. The decrease of the flux is because the grafting time of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide is too long, and an extra coating is formed on the surface of the membrane, which increases the water transmission resistance. When the grafting time of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide is 120 s, the flux is 2.3 L·m -2 ·h -1 ·bar -1 , and the NaCl rejection is 99.1%, which has no obvious difference from the performance of Comparative Example 1.

[0097] Example 5

[0098] The present Example 5 provides a preparation method of an anti-fouling polyamide reverse osmosis membrane with efficient photoinitiated polymerization grafting of zwitterionic groups, comprising the following steps:

[0099] (1) Fix the base membrane on a plate frame, pour the aqueous solution of m-phenylenediamine with a mass concentration of 5% on the surface of the base membrane and stand for 3-5 min, and then pour off the excess aqueous solution and dry the residual aqueous solution on the surface of the base membrane with an air knife;

[0100] (2) Pour the oil phase solution of 0.1% melitic acid chloride onto the surface of the membrane obtained in step (1), interfacial polymerization for 150 s to form a cross-linked polyamide separation layer, pour off the residual oil phase solution, and wash the unreacted organic acid chloride monomer with an organic solvent;

[0101] (3) Pour the 1% 4,4-diaminobenzophenone ethanol solution onto the surface of the TFC membrane prepared in step (2) to react with the residual acid chloride for 120 s, then pour off the excess photoinitiator solution and blow off the water droplets on the surface with an air knife;

[0102] (4) Pour the 3% aqueous solution of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide onto the surface of the membrane obtained in step (3) and irradiate under ultraviolet light for 120 s to graft the zwitterionic polymer, then pour off the excess zwitterionic aqueous solution and wash the surface of the membrane with deionized water;

[0103] (5) Heat treat the membrane obtained in step (4) in a 70°C oven for 3 min to obtain a polyamide reverse osmosis composite membrane;

[0104] The polyamide reverse osmosis membrane prepared by the above method was tested for separation performance, and the water production flux was 2.4 L·m -2 ·h -1 ·bar -1 , and the NaCl rejection was 99.3%.

[0105] As shown in Figure 2 , the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in Example 4 above and the polyamide reverse osmosis membrane of Comparative Example 1 were subjected to infrared and XPS characterization. Figure 2 (a) is the infrared spectrum of the reverse osmosis membrane, from which it can be seen that, compared with the polysulfone base membrane, all the reverse osmosis membranes have N-H in-plane bending vibration, N-H deformation vibration and C=O stretching vibration peaks at 1540 cm -1 , 1608 cm -1 and 1663 cm -1 , respectively, indicating that the polyamide layer is successfully prepared. The peak at 1725 cm -1 of the anti-fouling reverse osmosis membrane is the stretching vibration of the ester group formed by the phenolic hydroxyl group and the acid chloride, indicating that 4,4-dihydroxybenzophenone has reacted with melitic acid chloride and successfully introduced 4,4-dihydroxybenzophenone onto the membrane surface. The peak at 1039 cm -1 of the anti-fouling reverse osmosis membrane is attributed to the stretching vibration of -SO3-, indicating that the zwitterionic polymer is successfully grafted onto the membrane surface. Figure 2 (b) is the XPS spectrum of the reverse osmosis membrane, from which it can be seen that the anti-fouling reverse osmosis membrane has S element signal, proving that the zwitterion is successfully grafted.

[0106] As Figure 3 shown, the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in the above Example 4 and the polyamide reverse osmosis membrane of Comparative Example 1 were tested for surface wettability and surface energy. Compared with Comparative Example 1, the hydrophilicity of the anti-fouling reverse osmosis membrane grafted with zwitterions was enhanced, and the surface energy was increased, which was due to the grafting of hydrophilic zwitterions.

[0107] As Figure 4 shown, the performance of the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in the above Example 4 and the polyamide reverse osmosis membrane of Comparative Example 1 were compared. The flux rejection of the anti-fouling polyamide reverse osmosis membrane obtained in Example 4-4 was not reduced, which ensured the good separation performance of the polyamide reverse osmosis membrane.

[0108] The anti-fouling performance of organic pollutants of the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in the above Example 4 and the polyamide reverse osmosis membrane of Comparative Example 1 were tested, and the results are shown in Figure 5 . Figure 5 (a) is the normalized flux of the reverse osmosis membrane during the filtration of bovine serum protein, Figure 5 (b) is the anti-fouling index of the reverse osmosis membrane. It can be seen from Figure 5 that the anti-organic pollution effect of the anti-fouling polyamide reverse osmosis membrane obtained in Example 4-4 is obviously better than that of the polyamide reverse osmosis membrane obtained in Comparative Example 1. The reason is that the grafting of zwitterionic polymers on the membrane surface can effectively improve the hydrophilicity of the membrane surface, build a stable hydration layer on the membrane surface, increase the Gibbs free energy of the deposition of pollutants on the membrane surface, thereby inhibiting the deposition of pollutants on the membrane surface; in addition, the increase of the hydrophilicity of the membrane surface effectively inhibits the hydrophobic interaction between the membrane surface and the pollutants, and reduces the adsorption of the pollutants on the membrane surface.

[0109] The anti-fouling performance of inorganic pollutants of the anti-fouling polyamide reverse osmosis membrane with serial number 4-4 in the above Example 4 and the polyamide reverse osmosis membrane of Comparative Example 1 were tested, and the results are shown in Figure 6 . Figure 6 (a) is the normalized flux of the reverse osmosis membrane during the filtration of simulated gypsum solution, Figure 6 (b) is the anti-fouling index of the reverse osmosis membrane. It can be seen from Figure 6 that the anti-inorganic pollution effect of the anti-fouling polyamide reverse osmosis membrane obtained in Example 4-4 is obviously better than that of the polyamide reverse osmosis membrane obtained in Comparative Example 1. The reason is that the stronger hydrophilic membrane surface increases the energy barrier of heterogeneous nucleation, making it difficult for the membrane surface to form pollutant aggregates; in addition, the existence of the hydration layer on the membrane surface reduces the complexation between the Ca 2+ and -COOH groups, and reduces the possibility of forming a pollutant layer.

[0110] The above parts not mentioned can be realized by referring to the prior art.

[0111] Of course, the above description is not a limitation on the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the spirit and scope of the present application should also be included in the protection scope of the present application.

Claims

1. A method for preparing an anti-pollution reverse osmosis membrane, characterized in that: The zwitterionic polymer is rapidly grafted onto the membrane surface by using a photo-initiated polymerization reaction, comprising the following steps: (1) Fix the base film on the frame, apply the organic amine aqueous monomer solution to the surface of the base film and let it stand, then pour out the excess aqueous solution and blow dry the remaining aqueous solution on the surface of the base film with an air knife; (2) pouring the organic acid chloride oil phase solution onto the membrane surface obtained in step (1) to carry out interfacial polymerization reaction to form a cross-linked polyamide separation layer, discarding the remaining oil phase solution, and washing the unreacted organic acid chloride monomer with an organic solvent; (3) pouring the photoinitiator solution onto the surface of the film prepared in step (2) to react with the residual acyl chloride, then pouring out the excess photoinitiator solution and blowing away the water droplets on the surface with an air knife; The photoinitiator is at least one of 4-hydroxybenzophenone, 4-aminobenzophenone, 4,4-dihydroxybenzophenone or 4,4-diaminobenzophenone; wherein the mass concentration of the photoinitiator used is 0.1-10%; (4) pouring the zwitterionic aqueous solution onto the membrane surface obtained in step (3), irradiating the grafted zwitterionic polymer under ultraviolet light, then pouring off the excess zwitterionic aqueous solution and rinsing the membrane surface with deionized water; (5) The membrane obtained in step (4) is heat-treated in an oven to obtain an anti-fouling polyamide reverse osmosis membrane.

2. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, wherein: In the step (1), the organic amine aqueous phase monomer is m-phenylenediamine, and the standing time is 3 to 5 minutes; wherein the mass concentration of the m-phenylenediamine used is 0.1 to 10%.

3. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, wherein: In the step (1), the base membrane is one of a polysulfone ultrafiltration membrane, a polyethersulfone ultrafiltration membrane, a polyimide ultrafiltration membrane, a polyacrylonitrile ultrafiltration membrane, a polyethylene ultrafiltration membrane or a polypropylene ultrafiltration membrane.

4. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, wherein: In the step (2), the organic acid chloride is at least one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, pyromellitoyl chloride, malonyl chloride, glutaryl chloride, and fumaryl chloride; the organic solvent is at least one of n-hexane, cyclohexane, n-heptane, toluene, Isopar-G, Isopar-E, Isopar-H, Isopar-L, and Isopar-M; the mass concentration of the organic acid chloride oil phase solution is 0.01-2%; and the polymerization reaction time is 10-300 s.

5. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In the step (3), the reaction time of the photoinitiator and the acyl chloride is 10 to 150 seconds.

6. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In step (4), the zwitterion is at least one of [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonic acid propyl) ammonium hydroxide, methacryloyloxyethyl trimethyl ammonium chloride, 2-methacryloyloxyethyl phosphorylcholine or 3-((3-acrylamidopropyl)dimethylammonium) propionate; wherein the mass concentration of the zwitterion used is 0.1-5%.

7. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: The grafting time in step (4) is 10 to 150 seconds.

8. The method for preparing an anti-pollution reverse osmosis membrane according to claim 1, characterized in that: In the step (4), the heat treatment temperature is 50-90° C., and the heat treatment time is 30-300 s.

9. An anti-pollution reverse osmosis membrane prepared by the method for preparing an anti-pollution reverse osmosis membrane according to any one of claims 1 to 8.

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