A polyamide reverse osmosis membrane with high rejection rate and preparation method thereof

Abstract

The present invention discloses a polyamide reverse osmosis membrane with a high retention rate and a preparation method thereof, and relates to the field of membrane separation technology. By selecting a polyethersulfone ultrafiltration base membrane as a support layer, the basic characteristics of high mechanical strength and chemical resistance are guaranteed. By pre-treatment with sodium dodecyl sulfate solution, N,N,N-trimethyl chitosan and sodium deoxycholate, its hydrophilicity is enhanced, providing active sites for interfacial polymerization to form polyamide. By adding a surfactant to the aqueous phase solution, the diffusion rate of amine monomers in the interfacial polymerization reaction is accelerated. Modified silica is added to the oil phase solution to form a stable organosilicon graft layer on the surface of nano-silica. Tertiary butylhydroquinone is grafted on the surface of the nano-silica to reduce the attack of chlorine on the polyamide chain and improve its chlorine resistance. By regulating the surface charge of the base membrane, activating the interface, and introducing anti-chlorine groups, the retention rate of the polyamide reverse osmosis membrane for salt inorganic substances is improved.

Description

Technical Field

[0001] The invention relates to the technical field of membrane separation, in particular to a polyamide reverse osmosis membrane with a high rejection rate and a preparation method thereof. Background Art

[0002] Polyamide reverse osmosis membranes are high-performance separation membranes primarily made of polyamide (PA). They utilize high pressure to drive water molecules through a dense polyamide layer, trapping impurities such as dissolved salts, organic matter, and microorganisms, achieving deep water desalination and purification. They are a type of composite membrane, constructed from multiple layers of materials, primarily comprising a support layer, an intermediate layer, and a desalination layer. The support layer provides mechanical strength to withstand high pressures, while the intermediate layer acts as a transition layer connecting the support layer and the desalination layer, enhancing structural stability. The desalination layer, composed of polyamide material, forms a dense network structure through interfacial polymerization, responsible for trapping salts, organic matter, and microorganisms. Their high salt rejection rate, resistance to pollution, acid and alkali, high temperature, and low energy consumption have led to their widespread application in seawater desalination, drinking water purification, and industrial wastewater treatment.

[0003] Polyamide reverse osmosis membranes produced using existing technologies have weak bonding between the polyamide layer and the support layer, making them prone to delamination during long-term, high-pressure operation. The uneven pore size of the support layer can lead to localized stress concentration, accelerating membrane rupture. The negative surface charge of the desalination layer easily adsorbs positively charged contaminants (such as metal hydroxide colloids), and frequent chemical cleaning shortens the membrane's service life. Conventional interfacial polymerization membranes have low flux, and adopting high-flux membranes reduces their salt rejection rate, making it difficult to balance flux and salt rejection. The negative surface charge of polyamide reverse osmosis membranes and the charge characteristics of their surface functional groups (-COOH) directly influence the adsorption behavior of contaminants. Therefore, the present invention provides a polyamide reverse osmosis membrane with a high rejection rate and a method for its preparation to address the aforementioned technical issues. Summary of the Invention

[0004] The object of the present invention is to provide a polyamide reverse osmosis membrane with a high rejection rate and a preparation method thereof, so as to solve the problems raised in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] A method for preparing a polyamide reverse osmosis membrane with a high rejection rate comprises the following steps:

[0007] S1: immersing the polyethersulfone ultrafiltration base membrane in a sodium dodecyl sulfate (SDS) solution, taking it out after ultrasonication, immersing it in a transition solution, shaking it at a constant temperature to form an intermediate layer, taking it out, and immersing it in deionized water to obtain a pretreated base membrane;

[0008] S2: Mix m-phenylenediamine (MPD) and dodecyltrimethylammonium chloride, add deionized water, add surfactant, and stir to obtain an aqueous phase solution;

[0009] S3: dissolving trimesoyl chloride in n-decane, adding modified silica, and ultrasonically dispersing to obtain an oil phase solution;

[0010] S4: immersing the pretreated base membrane in an aqueous solution for 5 to 15 seconds, taking it out, and then directly immersing it in an oil phase solution for 10 to 30 seconds, taking it out, and immersing it in a 4-pyrrolidinopyridine (4-PPY) solution for 10 to 15 seconds to obtain a pretreated reverse osmosis membrane;

[0011] S5: Immerse the pretreated reverse osmosis membrane in a triethyl phosphate (TEP) solution, shake, take out, and dry to obtain a polyamide reverse osmosis membrane with a high rejection rate.

[0012] In the above technical effect, in step S1, the polyethersulfone ultrafiltration base membrane forming the intermediate layer is immersed in deionized water to flush the unreacted transition liquid on the surface of the base membrane, stabilize the membrane structure, prevent shrinkage and deformation, and avoid interference with subsequent interfacial polymerization reactions.

[0013] Furthermore, the transition solution includes the following components by mass: 0.05-0.2 parts of N,N,N-trimethyl chitosan (TMC), 10-15 parts of sodium deoxycholate, and 50-100 parts of deionized water.

[0014] Furthermore, the surfactant is sorbitan monolaurate (Span 20).

[0015] Furthermore, the SDS solution is a 0.1-5 wt% aqueous solution.

[0016] Furthermore, the TEP solution is a 0.05-0.1 wt% anhydrous ethanol solution.

[0017] In the above technical solution, polyethersulfone ultrafiltration base membrane is selected as the supporting layer. Compared with polyester non-woven fabrics and polysulfone base membranes in the prior art, it has higher mechanical strength and chemical resistance. Immersing it in SDS solution for ultrasonic treatment can reduce the hydrophobicity of the surface of the polyethersulfone ultrafiltration base membrane, while removing organic pollutants and residues on the surface of the base membrane, enhancing the adsorption capacity of the subsequent aqueous phase monomer MPD, and providing active sites for interfacial polymerization to form polyamide; through pretreatment with TMC and sodium deoxycholate, an intermediate layer is formed. The buffer system with TMC as the main component has good film-forming properties and is comparable to SDS. The negatively charged layer formed undergoes electrostatic interaction, forming a dense hydrophilic coating on the surface of the base membrane, optimizing the interface uniformity and stability while further reducing the contact angle and enhancing the hydrophilicity. During the initial separation process, the filter membrane is in a state of high flux. As the separation continues, the solutes on the membrane surface will increase significantly. The solutes are deposited or adsorbed on the membrane surface to form a contamination layer, which changes the pore size distribution or surface properties of the membrane and reduces the retention capacity of small molecule solutes. The interfacial charge distribution is regulated by the special amphiphilic structure of sodium deoxycholate, which can reduce the deposition of pollutants and improve the retention rate of the reverse osmosis membrane.

[0018] By adding sodium dodecylsulfonate to the aqueous solution, the interfacial tension between the aqueous phase and the organic phase is reduced, the diffusion rate of the amine monomer in the interfacial polymerization reaction is accelerated, and a uniform polyamide separation layer is formed; by adding dodecyltrimethylammonium chloride, under acidic conditions, its amino group is protonated to form -NH3 + , enhancing its reactivity with acyl chloride; Cl as an electron-withdrawing group can enhance the charge density of the polyamide chain and improve its ability to retain cations.

[0019] 4-PPY solution acts as a nucleophilic catalyst, promoting further reaction between residual acyl chloride groups (-COCl) and amine groups (-NH2) in the polyamide layer to generate a new layer rich in carboxyl groups, reducing the layer thickness while improving the surface hydrophilicity; TEP solution is used to post-treat and regulate the surface of the polyamide reverse osmosis membrane to remove the low-cross-linked polyamide on the surface, forming nano-scale pores and improving mass transfer efficiency.

[0020] Furthermore, in step S1, the process conditions of constant temperature shaking are: shaking at a temperature of 40-50° C. for 3-4 hours.

[0021] Furthermore, in step S1, the ultrasonic process conditions are: at a frequency of 20-50 kHz, a power of 100-200 W, and ultrasonication for 30-45 minutes.

[0022] Furthermore, in step S2, the mass ratio of m-phenylenediamine, dodecyltrimethylammonium chloride, deionized water, and surfactant is (2.5-3):3:90:0.4.

[0023] Furthermore, in step S2, the stirring process conditions are: stirring at a rotation speed of 300-500 rpm for 30-40 minutes.

[0024] Furthermore, in step S3, the mass ratio of trimesoyl chloride, n-decane, and modified silica is (0.5-1):70:2.

[0025] Furthermore, in step S3, the process conditions for ultrasonic dispersion are: a frequency of 50-100 kHz, a power of 250-500 W, and ultrasonication for 10-30 minutes.

[0026] Furthermore, in step S4, the 4-PPY solution is a 1-5 wt% anhydrous ethanol solution.

[0027] Furthermore, in step S5, the shaking process conditions are: shaking for 10-20 seconds at room temperature, and the drying process conditions are: drying at a temperature of 60-70° C. for 1-2 hours.

[0028] Further, the modified silica is prepared by the following steps:

[0029] Step 1: adding nano-silica to an ethanol solution, ultrasonically dispersing, adding an epoxy silane coupling agent, adding a buffer solution, and adjusting the pH to obtain coupled modified silica;

[0030] Step 2: Mix the coupled modified silica and tert-butylhydroquinone (TBHQ), add ethanol solution and sulfuric acid, stir, heat to react, centrifuge, wash with deionized water, and dry to obtain modified silica.

[0031] Furthermore, the buffer solution includes the following components by mass: 2 to 3 parts of disodium hydrogen phosphate, 1 to 2 parts of sodium dihydrogen phosphate, and 50 to 100 parts of deionized water.

[0032] Furthermore, in step 1, the pH is adjusted to 8-12.

[0033] Furthermore, in step 1, the mass ratio of nano-silica, ethanol solution, epoxy silane coupling agent, and buffer solution is (0.1-0.5):40:0.5:1.

[0034] Furthermore, in step 2, the mass ratio of the coupled modified silica, TBHQ, ethanol solution, and sulfuric acid is (0.1-0.5):0.1:40:0.1.

[0035] Furthermore, the ethanol solution is a 90-95% by volume aqueous solution.

[0036] Furthermore, in step 2, the centrifugal process conditions are: rotation speed 2400-3000 rpm, centrifugation time 30-40 min.

[0037] Furthermore, in step 2, the drying process conditions are: drying at a temperature of 60-70° C. for 1-2 hours.

[0038] Furthermore, the epoxysilane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560).

[0039] In the above technical solution, the surface of nano-silica is rich in silanol (Si-OH), which is ultrasonically dispersed in an ethanol solution to form a uniform suspension. The epoxy silane coupling agent generates an active silanol intermediate under the action of a buffer solution. The silanol and silanol form a siloxane bond (Si-O-Si) through a condensation reaction, forming a stable organic silicon graft layer on the surface of the nano-silica.

[0040] The epoxy group exposed at the other end of the epoxy silane coupling agent on the surface of nano-silica provides an active site for grafting anti-chlorine groups. Under acidic and heating conditions, the epoxy group undergoes a ring-opening reaction, and the phenolic hydroxyl group of tert-butylhydroquinone (TBHQ) acts as a nucleophile to attack the carbon atom in the epoxy group to form an ether bond, grafting TBHQ on the surface of nano-silica. Its benzene ring structure can further undergo free radical addition reaction with the epoxy group to produce partial cross-linking, forming a three-dimensional network structure, and improving its anti-chlorine performance.

[0041] The rejection rate of polyamide reverse osmosis membranes depends on their dense selective structure. The amide bond (-CO-NH-) is formed by interfacial polymerization of acyl chloride monomers and amine monomers. The main chain contains a large number of amide bonds, which are the main sites of oxidative attack. Free chlorine, as a strong oxidant, will directly attack the (NH) on the amide bond, causing oxidative breakage or chlorine substitution reaction, destroying the integrity of the polymer. By modifying nano-silica to introduce chlorine-resistant groups and adding modified silica to the oil phase, the attack of chlorine on the polyamide chain can be reduced, thereby improving the rejection rate of salt inorganic substances.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The polyamide reverse osmosis membrane of the present invention uses a polyethersulfone ultrafiltration base membrane with higher mechanical strength and chemical resistance as a support layer, and is immersed in an SDS solution for ultrasonic treatment, thereby reducing the hydrophobicity of the polyethersulfone ultrafiltration base membrane surface and enhancing the adsorption capacity of the subsequent aqueous phase monomer MPD. Through pretreatment with TMC and sodium deoxycholate, an intermediate layer is formed to optimize the interface uniformity and stability. By adding sodium deoxycholate, the deposition of pollutants is reduced and the rejection rate of the reverse osmosis membrane for small molecular solutes is improved.

[0044] 2. The polyamide reverse osmosis membrane of the present invention reduces the interfacial tension between the aqueous phase and the organic phase by adding sodium dodecyl sulfate to the aqueous phase solution, thereby accelerating the diffusion rate of amine monomers in the interfacial polymerization reaction; and enhances the reactivity of amino groups and acyl chloride groups and the charge density of the polyamide chain by adding dodecyltrimethylammonium chloride, thereby improving the retention capacity of cations.

[0045] 3. The polyamide reverse osmosis membrane of the present invention is treated with a 4-PPY solution to promote the further reaction of the residual acyl chloride groups in the polyamide layer with the amino groups to generate a new layer rich in carboxyl groups, thereby improving the surface hydrophilicity; the surface of the polyamide membrane is post-treated and regulated by a triethyl phosphate solution to remove the polyamide with low cross-linking degree on the surface, forming nano-scale pores and improving the mass transfer efficiency.

[0046] 4. The polyamide reverse osmosis membrane of the present invention forms a stable organic silicon graft layer by modifying the surface of nano-silica, grafting TBHQ on the surface of nano-silica, introducing anti-chlorine groups, reducing the attack of chlorine on the polyamide chain, and improving the retention rate of salt inorganic substances. DETAILED DESCRIPTION

[0047] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0048] In the following specific embodiments: the number of "parts" mentioned below is parts by mass;

[0049] The transition solution includes the following components by mass: 0.2 parts of N,N,N-trimethylchitosan (TMC), 10 parts of sodium deoxycholate, and 90 parts of deionized water.

[0050] The buffer solution includes the following components by mass: 2 parts of disodium hydrogen phosphate, 1 part of sodium dihydrogen phosphate, and 100 parts of deionized water.

[0051] The surfactant was sorbitan monolaurate (Span 20);

[0052] The sodium lauryl sulfate solution is a 0.5 wt% aqueous solution;

[0053] The triethyl phosphate (TEP) solution is a 0.08 wt% anhydrous ethanol solution;

[0054] 4-Pyrrolidinopyridine (4-PPY) solution is a 1.2 wt% anhydrous ethanol solution;

[0055] Ethanol solution is a 95v% aqueous solution;

[0056] The epoxysilane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560);

[0057] Polyethersulfone ultrafiltration base membrane, size φ100mm, pore size 0.22μm;

[0058] Nano-silica, model HL-200, average particle size 40nm;

[0059] Example 1: A method for preparing a polyamide reverse osmosis membrane with a high rejection rate, comprising the following steps:

[0060] S1: Immerse the polyethersulfone ultrafiltration base membrane in a sodium dodecyl sulfate solution, ultrasonicate at a frequency of 21 kHz and a power of 110 W for 32 minutes, remove it, immerse it in a transition solution, shake it at a temperature of 40°C for 3 hours to form an intermediate layer, remove it, and immerse it in deionized water to obtain a pretreated base membrane;

[0061] S2: m-phenylenediamine and dodecyltrimethylammonium chloride were mixed, deionized water and a surfactant were added, and the mixture was stirred at 300 rpm for 30 min to obtain an aqueous phase solution; the mass ratio of m-phenylenediamine, dodecyltrimethylammonium chloride, deionized water, and surfactant was 2.5:3:90:0.4;

[0062] S3: Dissolve trimesoyl chloride in n-decane, add modified silica, and sonicate for 10 min at a frequency of 55 kHz and a power of 250 W to obtain an oil phase solution; the mass ratio of trimesoyl chloride, n-decane, and modified silica is 0.5:70:2;

[0063] S4: immersing the pretreated base membrane in the aqueous solution for 5 seconds, taking it out, and then directly immersing it in the oil phase solution for 10 seconds, taking it out, and then immersing it in the 4-PPY solution for 10 seconds to obtain a pretreated reverse osmosis membrane;

[0064] S5: Immerse the pretreated reverse osmosis membrane in a triethyl phosphate solution, shake it for 10 seconds at room temperature, take it out, and heat-dry it at 60° C. for 1 hour to obtain a polyamide reverse osmosis membrane with a high retention rate.

[0065] In step S3, modified silica is prepared by the following steps:

[0066] Step 1: Add nano-silica to an ethanol solution, disperse it by ultrasonication, add an epoxy silane coupling agent, add a buffer solution, and adjust the pH to 8 to obtain coupled modified silica; the mass ratio of nano-silica, ethanol solution, epoxy silane coupling agent, and buffer solution is 0.1:40:0.5:1;

[0067] Step 2: Mix the coupled modified silica and tert-butylhydroquinone, add ethanol solution and sulfuric acid, stir, heat and react, centrifuge at 2400 rpm for 30 minutes, wash with deionized water, and dry at 60°C for 1 hour to obtain modified silica; the mass ratio of coupled modified silica, tert-butylhydroquinone, ethanol solution and sulfuric acid is 0.1:0.1:40:0.1.

[0068] Example 2: A method for preparing a polyamide reverse osmosis membrane with a high rejection rate, comprising the following steps:

[0069] S1: Immerse the polyethersulfone ultrafiltration base membrane in a sodium dodecyl sulfate solution, ultrasonicate at a frequency of 30 kHz and a power of 150 W for 35 minutes, remove it, immerse it in a transition solution, shake it at a temperature of 45°C for 3.5 hours to form an intermediate layer, remove it, and immerse it in deionized water to obtain a pretreated base membrane;

[0070] S2: m-phenylenediamine and dodecyltrimethylammonium chloride were mixed, deionized water and a surfactant were added, and the mixture was stirred at 400 rpm for 35 min to obtain an aqueous phase solution; the mass ratio of m-phenylenediamine, dodecyltrimethylammonium chloride, deionized water, and surfactant was 2.5:3:90:0.4;

[0071] S3: Dissolve trimesoyl chloride in n-decane, add modified silica, and sonicate for 20 min at a frequency of 60 kHz and a power of 300 W to obtain an oil phase solution; the mass ratio of trimesoyl chloride, n-decane, and modified silica is 0.5:70:2;

[0072] S4: immersing the pretreated base membrane in the aqueous solution for 5 seconds, taking it out, and then directly immersing it in the oil phase solution for 10 seconds, taking it out, and then immersing it in the 4-PPY solution for 12 seconds to obtain a pretreated reverse osmosis membrane;

[0073] S5: Immerse the pretreated reverse osmosis membrane in the TEP solution, shake it for 15 seconds at room temperature, take it out, and heat-dry it at 65° C. for 1.5 hours to obtain a polyamide reverse osmosis membrane with a high retention rate.

[0074] In step S3, modified silica is prepared by the following steps:

[0075] Step 1: Add nano-silica to an ethanol solution, ultrasonically disperse, add an epoxy silane coupling agent, add a buffer solution, and adjust the pH to 10 to obtain coupled modified silica; the mass ratio of nano-silica, ethanol solution, epoxy silane coupling agent, and buffer solution is 0.3:40:0.5:1;

[0076] Step 2: Mix the coupled modified silica and tert-butylhydroquinone (TBHQ), add ethanol solution and sulfuric acid, stir, heat and react, centrifuge at 2600 rpm for 35 minutes, wash with deionized water, and dry at 65°C for 1.5 hours to obtain modified silica; the mass ratio of coupled modified silica, TBHQ, ethanol solution and sulfuric acid is 0.4:0.1:40:0.1.

[0077] Example 3: A method for preparing a polyamide reverse osmosis membrane with a high rejection rate, comprising the following steps:

[0078] S1: Immerse the polyethersulfone ultrafiltration base membrane in a sodium dodecyl sulfate solution, ultrasonicate it at a frequency of 50 kHz and a power of 200 W for 45 minutes, then remove it, immerse it in a transition solution, shake it at a temperature of 50°C for 4 hours to form an intermediate layer, remove it, and immerse it in deionized water to obtain a pretreated base membrane;

[0079] S2: m-phenylenediamine and dodecyltrimethylammonium chloride were mixed, deionized water and a surfactant were added, and the mixture was stirred at 500 rpm for 40 min to obtain an aqueous phase solution; the mass ratio of m-phenylenediamine, dodecyltrimethylammonium chloride, deionized water, and surfactant was 3:3:90:0.4;

[0080] S3: Dissolve trimesoyl chloride in n-decane, add modified silica, and ultrasonicate at a frequency of 100 kHz and a power of 500 W for 30 minutes to obtain an oil phase solution; the mass ratio of trimesoyl chloride, n-decane, and modified silica is 1:70:2;

[0081] S4: immersing the pretreated base membrane in the aqueous solution for 15 seconds, taking it out, and then directly immersing it in the oil phase solution for 30 seconds, taking it out, and then immersing it in the 4-PPY solution for 15 seconds to obtain a pretreated reverse osmosis membrane;

[0082] S5: Immerse the pretreated reverse osmosis membrane in the TEP solution, shake it for 20 seconds at room temperature, take it out, and heat-dry it at 70° C. for 2 hours to obtain a polyamide reverse osmosis membrane with a high retention rate.

[0083] In step S3, modified silica is prepared by the following steps:

[0084] Step 1: Add nano-silica to an ethanol solution, disperse it by ultrasonication, add an epoxy silane coupling agent, add a buffer solution, and adjust the pH to 12 to obtain coupled modified silica; the mass ratio of nano-silica, ethanol solution, epoxy silane coupling agent, and buffer solution is 0.5:40:0.5:1;

[0085] Step 2: Mix the coupled modified silica and TBHQ, add ethanol solution and sulfuric acid, stir, heat and react, centrifuge at 3000 rpm for 40 minutes, wash with deionized water, and dry at 70°C for 2 hours to obtain modified silica; the mass ratio of coupled modified silica, TBHQ, ethanol solution and sulfuric acid is 0.5:0.1:40:0.1.

[0086] Comparative Example 1: A method for preparing a polyamide reverse osmosis membrane, comprising the following steps:

[0087] S1; The polyethersulfone ultrafiltration base membrane was immersed in a sodium dodecyl sulfate solution, ultrasonicated at a frequency of 20 kHz and a power of 100 W for 30 min, and then removed and immersed in deionized water to obtain a pretreated base membrane;

[0088] Steps S2, S3, and S4 are the same as those in Example 1.

[0089] Comparative Example 2: A method for preparing a polyamide reverse osmosis membrane, comprising the following steps:

[0090] S2: Add m-phenylenediamine to deionized water and a surfactant, and stir at 300 rpm for 30 min to obtain an aqueous phase solution; the mass ratio of m-phenylenediamine, deionized water, and surfactant is 2.5:90:0.4;

[0091] Steps S1, S3, and S4 are the same as those in Example 1.

[0092] Comparative Example 3: A method for preparing a polyamide reverse osmosis membrane, comprising the following steps:

[0093] S3: Dissolve trimesoyl chloride in n-decane and ultrasonicate for 10 min at a frequency of 50 kHz and a power of 250 W to obtain an oil phase solution; the mass ratio of trimesoyl chloride, n-decane, and modified silica is 0.5:70:2;

[0094] Steps S1, S2, S4, and S5 are the same as those in Example 1.

[0095] Comparative Example 4: A method for preparing a polyamide reverse osmosis membrane, comprising the following steps:

[0096] S4: immersing the pretreated base membrane in the aqueous solution for 5 seconds, taking it out, and then directly immersing it in the oil phase solution for 10 seconds, taking it out, to obtain a pretreated reverse osmosis membrane;

[0097] Steps S1, S2, S3, and S5 are the same as those in Example 1.

[0098] Comparative Example 5: A method for preparing a polyamide reverse osmosis membrane, comprising the following steps:

[0099] S3: Dissolve trimesoyl chloride in n-decane, add nano-silica, and ultrasonicate at a frequency of 55 kHz and a power of 250 W for 10 minutes to obtain an oil phase solution; the mass ratio of trimesoyl chloride, n-decane, and nano-silica is 0.5:70:2;

[0100] Steps S1, S2, S4, and S5 are the same as those in Example 1.

[0101] experiment:

[0102] The reverse osmosis membranes obtained in Examples 1-3 and Comparative Examples 1-4 were used to prepare samples, and their performance was tested and the test results were recorded:

[0103] Solution preparation: The concentration of sodium chloride (NaCl) solution is 1g / L; the concentration of sodium sulfate (Na2SO4) solution is 1g / L; the concentration of magnesium sulfate (MgSO4) solution is 1g / L;

[0104] Penetration test: Under room temperature, the effective area is 12.56cm 2 The membrane was placed in a homemade filtration system. Before testing, it was pre-pressed with a pressure of 0.7 MPa for 30 minutes to obtain a stable pure water flux.

[0105] NaCl retention rate: Using GB / T 32373-2015 as the reference standard, replace pure water with a 1g / L NaCl solution and run it steadily for 30 minutes to measure its retention rate.

[0106] Na2SO4 retention rate: Using GB / T 32373-2015 as the reference standard, replace pure water with a 1g / L Na2SO4 solution and run it steadily for 30 minutes to measure its retention rate;

[0107] MgSO4 retention rate: Using GB / T 32373-2015 as the reference standard, replace pure water with a 1g / L MgSO4 solution, run it steadily for 30 minutes, and measure its retention rate;

[0108] Performance comparison table

[0109]

[0110] According to the data in the above table, we can clearly draw the following conclusions:

[0111] The high-retention polyamide reverse osmosis membranes obtained in Examples 1-3 were compared with the polyamide reverse osmosis membranes obtained in Comparative Examples 1-4. The test results showed that, compared with the comparative examples, the high-retention polyamide reverse osmosis membranes obtained in Examples 1-3 had a large permeate flux, and had high permeate flux, NaCl retention rate, Na2SO4 retention rate, and MgSO4 retention rate.

[0112] Compared with Example 1, the polyamide reverse osmosis membrane obtained in Comparative Example 1 was not treated with a transition liquid, and the permeation flux, NaCl retention rate, Na2SO4 retention rate, and MgSO4 retention rate were lower, indicating that the transition liquid (a mixture of N,N,N-trimethyl chitosan and sodium deoxycholate) formed a dense hydrophilic coating through electrostatic interaction, optimized the interface uniformity, and enhanced the bonding force between the polyamide layer and the support layer.

[0113] Compared with Example 1, the polyamide reverse osmosis membrane obtained in Comparative Example 2 does not add dodecyltrimethylammonium chloride to the aqueous phase solution, and the permeation flux, NaCl retention rate, Na2SO4 retention rate, and MgSO4 retention rate are reduced, indicating that dodecyltrimethylammonium chloride can enhance the reactivity of amino groups and acyl chlorides under acidic conditions, accelerate the diffusion of amine monomers, promote uniform densification of the polyamide layer, and improve the retention rate of the polyamide reverse osmosis membrane.

[0114] Compared with Example 1, no modified nano-silica was added to the oil phase solution of the polyamide reverse osmosis membrane obtained in Comparative Example 3, and the permeation flux, NaCl retention rate, Na2SO4 retention rate, and MgSO4 retention rate were significantly reduced, indicating that tert-butylhydroquinone (TBHQ) on the surface of the modified silica formed a three-dimensional network structure through a free radical addition reaction, effectively inhibiting the oxidative attack of free chlorine on the polyamide chain and improving the retention rate of salt inorganic substances.

[0115] Compared with Example 1, the polyamide reverse osmosis membrane obtained in Comparative Example 4, after being immersed in the oil phase, was not immersed in the 4-PPY solution treatment, and the permeation flux, NaCl retention rate, Na2SO4 retention rate, and MgSO4 retention rate were significantly reduced, indicating that the polyamide reverse osmosis membrane prepared after treatment with the 4-PPY solution in the present invention was not as effective.

[0116] Compared with Example 1, the polyamide reverse osmosis membrane obtained in Comparative Example 5 was not modified with nano-silica after being immersed in the oil phase, and the permeation flux, NaCl retention rate, Na2SO4 retention rate, and MgSO4 retention rate were significantly reduced. The addition of only nano-silica as an inorganic filler did not have a high retention rate and good effect as the polyamide reverse osmosis membrane prepared by adding modified nano-silica in the present invention.

[0117] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A method for preparing a polyamide reverse osmosis membrane with a high rejection rate, characterized in that: The following steps are involved: S1: immersing the polyethersulfone ultrafiltration base membrane in a sodium dodecyl sulfate solution, taking it out after ultrasonication, immersing it in a transition solution, shaking it at a constant temperature to form an intermediate layer, taking it out, and immersing it in deionized water to obtain a pretreated base membrane; S2: Mix m-phenylenediamine and dodecyltrimethylammonium chloride, add deionized water, add a surfactant, and stir to obtain an aqueous solution; S3: dissolving trimesoyl chloride in n-decane, adding modified silica, and ultrasonically dispersing to obtain an oil phase solution; S4: immersing the pretreated base membrane in an aqueous solution and an oily solution in sequence, taking it out, and immersing it in 4-pyrrolidinopyridine to obtain a pretreated reverse osmosis membrane; S5: Immersing the pretreated reverse osmosis membrane in a triethyl phosphate solution, shaking, removing, and drying to obtain a polyamide reverse osmosis membrane with a high rejection rate; The transition liquid includes the following components by mass: 0.05-0.2 parts of N-trimethyl chitosan, 10-15 parts of sodium deoxycholate, and 50-100 parts of deionized water.

2. The method for preparing a polyamide reverse osmosis membrane with a high rejection rate according to claim 1, wherein: The modified silicon dioxide is prepared by the following steps: Step 1: adding nano-silica to an ethanol solution, ultrasonically dispersing, adding an epoxy silane coupling agent, adding a buffer solution, and adjusting the pH to obtain coupled modified silica; Step 2: Mix the coupled modified silica and tert-butylhydroquinone, then add ethanol solution and sulfuric acid, stir thoroughly, heat to react, centrifuge, wash with deionized water, and dry to obtain modified silica.

3. The method for preparing a polyamide reverse osmosis membrane with a high rejection rate according to claim 1, wherein: The surfactant is sorbitol monolaurate; the sodium lauryl sulfate solution is a 0.1-5 wt% aqueous solution; and the triethyl phosphate solution is a 0.05-0.1 wt% anhydrous ethanol solution.

4. The method for preparing a polyamide reverse osmosis membrane with a high rejection rate according to claim 2, wherein: In step 1, the mass ratio of nano-silica, ethanol solution, epoxy silane coupling agent, and buffer solution is (0.1-0.5):40:0.5:

1.

5. The method for preparing a polyamide reverse osmosis membrane with a high rejection rate according to claim 2, wherein: In step 2, the mass ratio of the coupled modified silica, tert-butylhydroquinone, ethanol solution, and sulfuric acid is (0.1-0.5):0.1:40:0.

1.

6. The method for preparing a polyamide reverse osmosis membrane with a high rejection rate according to claim 1, wherein: In step S2, the mass ratio of m-phenylenediamine, dodecyltrimethylammonium chloride, deionized water, and surfactant is (2.5-3):3:90:0.

4.

7. The method for preparing a polyamide reverse osmosis membrane with a high rejection rate according to claim 1, wherein: In step S3, the mass ratio of trimesoyl chloride, n-decane, and modified silica is (0.5-1):70:

2.

8. The method for preparing a polyamide reverse osmosis membrane with a high rejection rate according to claim 2, wherein: The epoxysilane coupling agent is γ-(2,3-epoxypropoxy)propyltrimethoxysilane.

9. A polyamide reverse osmosis membrane with a high rejection rate, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 8.

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