A polyamine protonated programmed polyamide reverse osmosis membrane and a preparation method thereof

Abstract

The application relates to the technical field of reverse osmosis membrane preparation, and discloses a polyamine protonization programmed polyamide reverse osmosis membrane and a preparation method thereof. The reverse osmosis membrane comprises a polysulfone ultrafiltration membrane and a polyamide separation layer formed on the surface of the polysulfone ultrafiltration membrane. The polyamide separation layer is formed by interfacial polymerization of an aqueous phase solution containing m-phenylenediamine, camphor sulfonic acid and tri(2-aminoethyl)amine and an organic phase solution containing triformylchloride. The mass fraction of tri(2-aminoethyl)amine is preset as 0.4 wt.%-1.5 wt.%, the pH of the aqueous phase is 7.5-10.5, and the aqueous phase is in a protonation enrichment function dominant mode or a deprotonation cross-linking function dominant mode. After water phase adsorption, interfacial polymerization, heat treatment, flushing and drying, the polyamide reverse osmosis membrane with corresponding salt rejection performance and water permeability is obtained.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis membrane technology, and in particular to a polyamine protonated programmed polyamide reverse osmosis membrane and its preparation method. Background Technology

[0002] Polyamide composite reverse osmosis membranes typically consist of a porous support membrane and a polyamide separation layer formed on the surface of the porous support membrane. The polyamide separation layer is generally prepared by interfacial polymerization of m-phenylenediamine and trimesoyl chloride. During preparation, an aqueous solution containing m-phenylenediamine is first adsorbed onto the surface of the support membrane, and then comes into contact with an organic solution containing trimesoyl chloride. The two monomers undergo a polymerization reaction at the interface between the aqueous and organic phases to form the polyamide layer with separation function. The thickness, crosslinking state, free volume, and separation pore size of the polyamide layer affect the water permeation flux and salt rejection performance of the reverse osmosis membrane.

[0003] Existing technologies typically regulate the formation process of polyamide layers by adjusting the concentration of m-phenylenediamine or trimesoyl chloride, interfacial polymerization time, heat treatment conditions, and pH of the reaction system, or by adding functional additives to the aqueous phase. Polyamine compounds contain multiple amino sites, which can affect the distribution of aqueous monomers near the interface and may also participate in interfacial polymerization as copolymer components; therefore, they have been used to modify polyamide reverse osmosis membranes.

[0004] Tris(2-aminoethyl)amine is an aliphatic polyamine containing one tertiary amine group and three primary amine groups. Existing film-forming methods typically incorporate tris(2-aminoethyl)amine as a functional additive or copolymer component into the aqueous phase, adjusting the polyamide layer structure by varying its dosage. In these methods, the concentration of tris(2-aminoethyl)amine is primarily investigated as an addition amount or reactant ratio; its impact on interfacial polymerization usually requires further experimental screening in conjunction with different monomer concentrations, reaction times, and processing conditions.

[0005] The protonation degree of the primary amine group in tris(2-aminoethyl)amine varies with the pH of the aqueous phase. When the primary amine group is at a higher protonation degree, its ability to participate in acyl chloride reactions is limited, but it can affect the distribution of m-phenylenediamine near the interface. When the primary amine group is at a lower protonation degree, the unprotonated primary amine group can react with trimesoyl chloride and participate in the formation of the polyamide network. Therefore, the role of tris(2-aminoethyl)amine in the aqueous phase is related not only to the amount added but also to its initial protonation state.

[0006] Some existing methods utilize local pH changes generated during interfacial polymerization to cause amine additives to undergo protonation or deprotonation during the reaction. Interfacial polymerization is accompanied by hydrochloric acid generation, and the local pH is affected by factors such as monomer diffusion, interfacial reaction rate, hydrochloric acid diffusion, and local accumulation. Therefore, the protonation state of the additive often changes with the reaction process, and its specific functioning state is not easy to determine before the start of interfacial polymerization. When using this dynamic response method, the duration and extent of the additive's action may vary with actual reaction conditions, making it inconvenient to pre-set the corresponding interfacial polymerization state according to membrane performance requirements.

[0007] To this end, a polyamine protonated programmed polyamide reverse osmosis membrane and its preparation method are proposed. Summary of the Invention

[0008] The technical solution of the present invention is implemented as follows: a polyamine protonated programmed polyamide reverse osmosis membrane, comprising a polysulfone ultrafiltration membrane and a polyamide separation layer formed on the surface of the polysulfone ultrafiltration membrane, wherein the polyamide separation layer is formed by interfacial polymerization of an aqueous phase solution containing m-phenylenediamine, camphor sulfonic acid and tris(2-aminoethyl)amine and an organic phase solution containing trimesoyl chloride.

[0009] The tris(2-aminoethyl)amine in the aqueous solution has a mass fraction of 0.4 wt.% to 1.5 wt.%, a pH value of 7.5 to 10.5, and contains no added acid-base adjusters. Therefore, the initial pH of the aqueous solution varies with the concentration of added tris(2-aminoethyl)amine, allowing the tris(2-aminoethyl)amine to form a protonated state before interfacial polymerization begins.

[0010] The mass fraction of tris(2-aminoethyl)amine in the aqueous solution is 0.4 wt.% to 0.5 wt.%, and the pH value of the aqueous solution is 7.5 to 8.5. Tris(2-aminoethyl)amine is in the protonation enrichment mode, and the average number of the three primary amine groups in its molecule in the protonated state is not less than 2.

[0011] Under test conditions of a 2000 mg / L NaCl aqueous solution as feed, a filtration pressure of 1.55 MPa, a temperature of 25 ± 1 ℃, and a cross-flow rate of 80 L / h, the water permeation flux of the polyamine protonated programmed polyamide reverse osmosis membrane prepared using the above-mentioned preparation range was 51.4–55.7 L·m⁻². -2 ·h -1 The NaCl retention rate is 99.08%–99.35%.

[0012] The mass fraction of tris(2-aminoethyl)amine in the aqueous solution is 0.8 wt.% to 1.5 wt.%, and the pH value of the aqueous solution is 9.5 to 10.5. Tris(2-aminoethyl)amine is in the deprotonated crosslinking mode, and the average number of the three primary amine groups in its molecule in the protonated state is no greater than 1.

[0013] Under test conditions of a 2000 mg / L NaCl aqueous solution as feed, a filtration pressure of 1.55 MPa, a temperature of 25 ± 1 °C, and a cross-flow rate of 80 L / h, the water permeation flux of the polyamine protonated programmed polyamide reverse osmosis membrane prepared using the above-mentioned preparation range was 64.2–75.1 L·m⁻². -2 ·h -1 The NaCl retention rate is 98.51% to 98.81%.

[0014] The polyamide separation layer has a thickness of 141.5–205.3 nm, a surface roughness of 28.9–56.2 nm, a free volume fraction of 18.35%–22.04%, and a separation pore size of 0.205–0.234 nm; the polyamine protonated programmed polyamide reverse osmosis membrane has a molecular weight cutoff of 80–98 Da.

[0015] This invention also provides a method for preparing a polyamine protonated programmed polyamide reverse osmosis membrane, comprising the following steps: S1. Dissolve m-phenylenediamine, camphor sulfonic acid and tris(2-aminoethyl)amine in water to prepare an aqueous solution. Control the mass fraction of tris(2-aminoethyl)amine in the aqueous solution to be 0.4 wt.% to 1.5 wt.%, and do not add acid-base adjusters to make the pH value of the aqueous solution 7.5 to 10.5. Preset the protonation state of tris(2-aminoethyl)amine to the corresponding functional dominant mode. S2. The aqueous solution obtained in step S1 is poured onto the surface of the polysulfone ultrafiltration membrane, and after standing, the excess aqueous solution is removed to obtain an aqueous adsorption membrane. S3. Coat the surface of the aqueous adsorption membrane prepared in step S2 with an organic phase solution containing pyromellitic chloride, let it stand to carry out interfacial polymerization reaction, and then remove the excess organic phase solution to obtain the interfacial polymerization precursor membrane. S4. The interfacial polymerization precursor membrane obtained in step S3 is subjected to heat treatment to obtain a polyamine protonated programmed polyamide reverse osmosis membrane.

[0016] In step S1, the mass fraction of m-phenylenediamine in the aqueous solution is 1.5 wt.% to 2.0 wt.%, and the mass fraction of camphor sulfonic acid in the aqueous solution is 1.5 wt.% to 2.5 wt.%.

[0017] In step S2, the pure water flux of the polysulfone ultrafiltration membrane at a cross-flow filtration pressure of 0.2 MPa is 150–180 L·m⁻¹. -2 ·h -1 The pore size is 30–60 nm, and the membrane cross-section has a sponge-like structure. The aqueous solution is allowed to stand on the surface of the polysulfone ultrafiltration membrane for 30–120 s. After removing the excess aqueous solution, the residual aqueous solution on the membrane surface is blown off with nitrogen.

[0018] In step S3, the organic phase solution uses n-hexane as the solvent, the mass fraction of pyromellitic chloride in the organic phase solution is 0.1 wt.% to 0.15 wt.%, and the interfacial polymerization reaction time is 30 to 120 s.

[0019] In step S4, the heat treatment temperature is 80–120 °C and the heat treatment time is 180–300 s; after the heat treatment is completed, the obtained membrane is cooled, rinsed with deionized water and dried.

[0020] The embodiments of the present invention have the following advantages due to the adoption of the above technical solutions: I. This invention determines the dominant mode of protonation enrichment or deprotonation crosslinking function of tris(2-aminoethyl)amine before the start of interfacial polymerization by setting the concentration of tris(2-aminoethyl)amine, thereby reducing the dependence of the additive state on local pH changes during the reaction and providing clearer initial conditions for the regulation of interfacial polymerization.

[0021] II. This invention establishes a correspondence between the concentration of tris(2-aminoethyl)amine and its dominant functional state. By adjusting a single concentration parameter, its role in interfacial polymerization can be changed, and the structure and membrane separation performance of the resulting polyamide separation layer can be adjusted according to the corresponding concentration range.

[0022] Third, the present invention does not change the main process of interfacial polymerization of m-phenylenediamine and trimesoyl chloride, nor does it require the addition of signal detection, feedback control or dynamic feeding devices. It only requires adjusting the concentration of tris(2-aminoethyl)amine in the aqueous phase preparation stage, which is convenient for connection with the existing polyamide composite reverse osmosis membrane preparation process.

[0023] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of the invention will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description

[0024] Figure 1 The images shown are scanning electron microscope images of the polyamide reverse osmosis membrane obtained in Example 1 of the present invention, wherein (a) is a surface morphology image of the polyamide separation layer and (b) is a cross-sectional morphology image of the polyamide separation layer. Figure 2 The images shown are scanning electron microscope images of the polyamide reverse osmosis membrane obtained in Example 4 of the present invention, wherein (a) is a surface morphology image of the polyamide separation layer and (b) is a cross-sectional morphology image of the polyamide separation layer. Figure 3 The images shown are scanning electron microscope images of the polyamide reverse osmosis membrane obtained in Comparative Example 4 of the present invention, wherein (a) is a surface morphology image of the polyamide separation layer and (b) is a cross-sectional morphology image of the polyamide separation layer. Figure 4 An atomic force microscope image of the polyamide reverse osmosis membrane obtained in Example 1 of this invention; Figure 5 An atomic force microscope image of the polyamide reverse osmosis membrane obtained in Example 4 of this invention; Figure 6 This is an atomic force microscope image of the polyamide reverse osmosis membrane obtained in Comparative Example 4 of the present invention; Figure 7 This is a simulation diagram of the free volume fraction of the polyamide separation layer obtained in Example 1 of the present invention; Figure 8 This is a simulation diagram of the free volume fraction of the polyamide separation layer obtained in Example 4 of the present invention; Figure 9 This is a simulation diagram of the free volume fraction of the polyamide separation layer obtained in Comparative Example 4 of the present invention; Figure 10 This is a comparison chart of the molecular weight cutoff and separation pore size of the polyamide reverse osmosis membranes obtained in Examples 1, 4 and Comparative Example 4 of the present invention. Detailed Implementation

[0025] This invention provides a polyamine protonated programmed polyamide reverse osmosis membrane, including a polysulfone ultrafiltration membrane and a polyamide separation layer formed on the surface of the polysulfone ultrafiltration membrane. During preparation, an aqueous phase solution is prepared with m-phenylenediamine, camphor sulfonic acid and tris(2-aminoethyl)amine, and an organic phase solution is prepared with pyromellitic trimethylol chloride and n-hexane. After aqueous phase adsorption, interfacial polymerization and heat treatment, a polyamide separation layer is formed on the surface of the polysulfone ultrafiltration membrane.

[0026] In this embodiment, the addition conditions of m-phenylenediamine and camphor sulfonic acid remain unchanged, and no acid-base regulator is added to the aqueous solution. By adjusting the addition concentration of tri(2-aminoethyl)amine, the aqueous solution is made to form the corresponding initial pH. When the mass fraction of tri(2-aminoethyl)amine is 0.4 wt.% to 0.5 wt.%, the pH of the aqueous solution is 7.5 to 8.5, and tri(2-aminoethyl)amine mainly functions as a protonation enrichment agent. When its mass fraction is 0.8 wt.% to 1.5 wt.%, the pH of the aqueous solution is 9.5 to 10.5, the role of unprotonated primary amine groups in interfacial polymerization increases, and a deprotonation crosslinking function dominates the mode.

[0027] During the process, the mass fraction of intermediate-phenylenediamine in the aqueous solution can be 1.5 wt.%–2.0 wt.%, and the mass fraction of camphor sulfonic acid can be 1.5 wt.%–2.5 wt.%. The settling time of the aqueous solution on the surface of the polysulfone ultrafiltration membrane can be 30–120 s. The mass fraction of trimesoyl chloride in the organic solution can be 0.1 wt.%–0.15 wt.%, the solvent is n-hexane, and the interfacial polymerization time can be 30–120 s. After interfacial polymerization, it can be heat-treated at 80–120 °C for 180–300 s.

[0028] The main raw materials and reagents used in this embodiment include: a polysulfone ultrafiltration membrane with a pure water flux of 150–180 L·m⁻¹ at a cross-flow filtration pressure of 0.2 MPa. -2 ·h -1 The membrane has a pore size of 30–60 nm and a sponge-like cross-section; m-phenylenediamine with a purity of 99%; trimesoyl chloride with a purity of 98%; tris(2-aminoethyl)amine with a purity of 98%; triethylamine with a purity of 99%; n-hexane and camphor sulfonic acid, both with a purity of not less than 98%; sodium chloride, analytical grade; sodium hydroxide and sulfuric acid, both with a purity of not less than 99%; nitrogen and deionized water.

[0029] Example 1 This embodiment provides a polyamine protonated programmed polyamide reverse osmosis membrane, comprising a polysulfone ultrafiltration membrane and a polyamide separation layer formed on the surface of the polysulfone ultrafiltration membrane, and its preparation process is as follows: S1. Select a surface area of ​​81 cm² 2 A polysulfone ultrafiltration membrane with no visible droplets on its surface is flattened and fixed onto a membrane frame. S2. Prepare an aqueous solution with a volume of 0.025 L, wherein the mass fraction of intermediate-phenylenediamine in the aqueous solution is 2.0 wt.%, the mass fraction of camphor sulfonic acid is 2.3 wt.%, the mass fraction of tris(2-aminoethyl)amine is 0.4 wt.%, and the solvent is deionized water; Without adding any acid-base adjuster, the pH of the aqueous solution was measured to be 7.5. The aqueous solution was poured onto the surface of the polysulfone ultrafiltration membrane and allowed to stand for 90 seconds to allow the aqueous components to be adsorbed onto the surface of the polysulfone ultrafiltration membrane. Then, the excess aqueous solution was removed, and the residual aqueous solution on the membrane surface was blown off with nitrogen to obtain an aqueous adsorption membrane. S3. Prepare an organic phase solution with a volume of 0.025 L, wherein the mass fraction of trimesoyl chloride in the organic phase solution is 0.1 wt.%, and the solvent is n-hexane; coat the organic phase solution onto the surface of the aqueous phase adsorption membrane, and let it stand for 60 s to allow the amine monomers in the aqueous phase and the trimesoyl chloride in the organic phase to undergo interfacial polymerization at the interface between the two phases; then remove the excess organic phase solution to obtain the interfacial polymerization precursor membrane; S4. The interfacial polymerization precursor membrane is heat-treated at 80 ℃ for 300 s. After the heat treatment is completed, it is cooled, rinsed with deionized water and dried to obtain a polyamine protonated programmed polyamide reverse osmosis membrane.

[0030] In this embodiment, the average number of the three primary amine groups in the tri(2-aminoethyl)amine molecule in the protonated state is 3, and the tri(2-aminoethyl)amine is in the protonation enrichment function-dominated mode.

[0031] Example 2 This embodiment provides a polyamine protonated programmed polyamide reverse osmosis membrane, the preparation steps of which are the same as those in Example 1, except that the mass fraction of tris(2-aminoethyl)amine in step S2 is 0.5 wt.

[0032] No external acid-base adjuster was added in this embodiment. The pH of the resulting aqueous solution was 8.5. The average number of the three primary amine groups in the tri(2-aminoethyl)amine molecule in the protonated state was 2. The tri(2-aminoethyl)amine was in the protonation enrichment mode. The other raw material amounts, aqueous phase standing time, interfacial polymerization conditions and heat treatment conditions were the same as in Example 1.

[0033] Example 3 This embodiment provides a polyamine protonated programmed polyamide reverse osmosis membrane, the preparation steps of which are the same as those in Example 1, except that the mass fraction of tris(2-aminoethyl)amine in step S2 is 0.8 wt.

[0034] No external acid-base adjuster was added in this embodiment, and the pH of the resulting aqueous solution was 9.5. The average number of the three primary amine groups in the tri(2-aminoethyl)amine molecule in the protonated state was calculated as 1. The role of the unprotonated primary amine groups in interfacial polymerization was increased, and the tri(2-aminoethyl)amine was in the deprotonated crosslinking function-dominated mode. The other preparation conditions were the same as in Example 1.

[0035] Example 4 This embodiment provides a polyamine protonated programmed polyamide reverse osmosis membrane, the preparation steps of which are the same as those in Example 1, except that the mass fraction of tris(2-aminoethyl)amine in step S2 is 1.5 wt.

[0036] No external acid-base adjuster was added in this embodiment. The pH of the resulting aqueous solution was 10.5. The average number of the three primary amine groups in the tri(2-aminoethyl)amine molecule in the protonated state was 0. The unprotonated primary amine groups could react with trimesoyl chloride. The tri(2-aminoethyl)amine was in the deprotonated crosslinking functional dominant mode. The other preparation conditions were the same as in Example 1.

[0037] Comparative Example 1 The preparation steps of this comparative example are the same as those of Example 1, except that tri(2-aminoethyl)amine is not added in step S2, but instead 0.3 wt.% triethylamine is added, and the pH of the resulting aqueous solution is 7.5. The remaining preparation conditions are the same as those of Example 1.

[0038] Comparative Example 2 The preparation steps of this comparative example are the same as those of Example 1, except that tri(2-aminoethyl)amine is not added in step S2, but instead 0.4 wt.% triethylamine is added, and the pH of the resulting aqueous solution is 8.5. The remaining preparation conditions are the same as those of Example 1.

[0039] Comparative Example 3 The preparation steps of this comparative example are the same as those of Example 1, except that tri(2-aminoethyl)amine is not added in step S2, but instead 0.7 wt.% triethylamine is added, and the pH of the resulting aqueous solution is 9.5. The other preparation conditions are the same as those of Example 1.

[0040] Comparative Example 4 The preparation steps of this comparative example are the same as those of Example 1, except that tri(2-aminoethyl)amine is not added in step S2, but triethylamine with a mass fraction of 1.3 wt.% is added instead, and the pH of the resulting aqueous solution is 10.5. The other preparation conditions are the same as those of Example 1.

[0041] Comparative Examples 1-4 were used to compare the effects of tri(2-aminoethyl)amine and triethylamine on interfacial polymerization and the performance of the resulting reverse osmosis membranes under the same aqueous phase pH conditions. Triethylamine does not contain primary amine groups that can undergo amidation reactions with trimesoyl chloride and cannot participate in the formation of polyamide networks in the same manner as tri(2-aminoethyl)amine.

[0042] Comparative Example 5 The preparation steps of this comparative example are the same as those of Example 1, except that tris(2-aminoethyl)amine is not added in step S2, and sodium hydroxide with a mass fraction of 0.05 wt.% is added to the aqueous phase solution to adjust the pH of the aqueous phase solution to 7.5. The remaining preparation conditions are the same as those of Example 1.

[0043] Comparative Example 6 The preparation steps of this comparative example are the same as those of Example 1, except that tris(2-aminoethyl)amine is not added in step S2, and sodium hydroxide with a mass fraction of 0.08 wt.% is added to the aqueous phase solution to adjust the pH of the aqueous phase solution to 8.5. The remaining preparation conditions are the same as those of Example 1.

[0044] Comparative Example 7 The preparation steps of this comparative example are the same as those of Example 1, except that tris(2-aminoethyl)amine is not added in step S2, and sodium hydroxide with a mass fraction of 0.14 wt.% is added to the aqueous phase solution to adjust the pH of the aqueous phase solution to 9.5. The remaining preparation conditions are the same as those of Example 1.

[0045] Comparative Example 8 The preparation steps of this comparative example are the same as those of Example 1, except that tris(2-aminoethyl)amine is not added in step S2, and sodium hydroxide with a mass fraction of 0.2 wt.% is added to the aqueous phase solution to adjust the pH of the aqueous phase solution to 10.5. The remaining preparation conditions are the same as those of Example 1.

[0046] Comparative Examples 5-8 were used to investigate the performance changes of the polyamide reverse osmosis membranes obtained when no tris(2-aminoethyl)amine was added and only inorganic alkali was used to adjust the pH of the aqueous phase.

[0047] Comparative Example 9 The preparation steps of this comparative example are the same as those of Example 1, except that the mass fraction of tris(2-aminoethyl)amine in step S2 is 0.3 wt.%.

[0048] No external acid-base adjuster was added in this comparative example, and the pH of the resulting aqueous solution was 6.2. The other preparation conditions were the same as in Example 1.

[0049] Comparative Example 10 The preparation steps of this comparative example are the same as those of Example 1, except that the mass fraction of tris(2-aminoethyl)amine in step S2 is 1.6 wt.%.

[0050] No external acid-base adjuster was added in this comparative example, and the pH of the resulting aqueous solution was 12.3. The other preparation conditions were the same as in Example 1.

[0051] Comparative Examples 9 and 10 were used to investigate the changes in the initial pH of the aqueous phase and the reverse osmosis membrane separation performance when the mass fraction of tris(2-aminoethyl)amine was below 0.4 wt.% and above 1.5 wt.%, respectively.

[0052] The amount of amino protonation was determined: Based on their properties, the acidity coefficients (pKa) of the three primary amines of tris(2-aminoethyl)amine (TAEA) are 9.85, 9.37, and 8.89, respectively; pKa is the negative logarithm of the acid dissociation constant Ka, used to represent the proton dissociation equilibrium of the corresponding group; for weak base B and its conjugate acid... The relationship between pH and pKa satisfies the Henderson-Hasselbalch equation:

[0053] Based on the above equations, the existing forms of the three primary amines (NH2) of TAEA under different pH conditions can be calculated, and the amount of protonation can be determined. when , When [NH2] = [NH3] + In this case, the concentration of the weak base is equal to that of its conjugate acid; when , At that time, [NH2] > [NH3] + The weak base molecular type (NH2) is dominant.

[0054] when , At that time, [NH2] < [NH3] + ], the ionic form of a weak base (NH3) + ) dominates.

[0055] Test Example 1 The reverse osmosis membranes obtained in Examples 1-4 and Comparative Examples 1-10 were tested using a cross-flow filtration device. Each membrane was equipped with three parallel filtration units, and the effective filtration area of ​​the membrane pool was 23.55 cm². 2 .

[0056] A 2000 mg / L NaCl aqueous solution was used as the feed solution with a pH of 7.0 ± 0.5. Before the test, the membrane sample was pre-pressurized for 30 min at a filtration pressure of 1.55 MPa and a temperature of 25 ± 1 ℃. Then, the filtration pressure was maintained at 1.55 MPa and the cross-flow rate was 80 L / h, and the permeate was collected.

[0057] Water permeation flux is calculated using the following formula:

[0058] In the formula, Water permeation flux, in L·m -2 ·h -1 ; For time The volume of permeate collected internally, in liters (L). Effective membrane area, in m² 2 ; The infiltration time is expressed in hours (h).

[0059] The NaCl rejection rate is calculated using the following formula:

[0060] In the formula, The NaCl rejection rate is expressed as % (%). This represents the NaCl concentration in the permeate, expressed in mg / L. This represents the NaCl concentration in the feed solution, expressed in mg / L.

[0061] The pH and Zeta potential of each aqueous solution were measured, and the results of the reverse osmosis membrane separation performance test are shown in Table 1.

[0062] Table 1. Characterization and separation performance test results of reverse osmosis membranes

[0063] As shown in Table 1, in Examples 1-4, as the mass fraction of tris(2-aminoethyl)amine increased from 0.4 wt.% to 1.5 wt.%, the pH of the aqueous solution increased from 7.5 to 10.5, the Zeta potential changed from 0.6 mV to -10.7 mV, and the average number of protonated primary amine groups in the tris(2-aminoethyl)amine molecule decreased from 3 to 0. Since no external acid-base adjuster was added in Examples 1-4, the above changes indicate that in these examples, the concentration of added tris(2-aminoethyl)amine can be used as a control parameter for the initial pH and protonated state of the aqueous phase.

[0064] In Examples 1 and 2, the mass fraction of tris(2-aminoethyl)amine was 0.4 wt.%–0.5 wt.%, the pH of the aqueous solution was 7.5–8.5, the average number of protonated primary amine groups was not less than 2, and tris(2-aminoethyl)amine was in the protonation enrichment dominant mode. The water permeation flux of the resulting membrane was 51.4–55.7 L·m⁻¹. -2 ·h -1 The NaCl rejection rate was 99.08%–99.35%, indicating that the polyamide separation layer prepared in this concentration range tended to have salt rejection performance.

[0065] In Examples 3 and 4, the mass fraction of tris(2-aminoethyl)amine was 0.8 wt.%–1.5 wt.%, the pH of the aqueous solution was 9.5–10.5, and the average number of protonated primary amine groups was no greater than 1. As the proportion of unprotonated primary amine groups increased, their participation in the interfacial polymerization with trimesoyl chloride was enhanced, and the water permeation flux of the resulting membrane was 64.2–75.1 L·m⁻¹. -2 ·h -1 The NaCl rejection rate was 98.51%–98.81%, indicating that the polyamide separation layer prepared within this concentration range has a large water transport capacity. The performance data and protonation state changes in Table 1 correspond to each other.

[0066] Comparative Examples 1–4 used triethylamine instead of tris(2-aminoethyl)amine, and the aqueous phase pH was also between 7.5 and 10.5, but the water permeation flux of the resulting membranes was only 49.7–51.6 L·m⁻¹.-2 ·h -1 No gradient changes as seen in Examples 1-4 were observed. The "average number of protonated primary amine groups" for Comparative Examples 1-4 in Table 1 is recorded as 0, which only indicates that they do not contain the three primary amine groups of tri(2-aminoethyl)amine, and does not mean that triethylamine itself cannot undergo protonation; triethylamine lacks primary amine groups that can form a polyamide network with trimesoyl chloride, and therefore cannot simultaneously play the roles of interfacial state regulation and copolymerization.

[0067] Comparative Examples 5–8 did not contain tris(2-aminoethyl)amine; the pH of the aqueous phase was adjusted to 7.5–10.5 using only sodium hydroxide. The resulting membranes exhibited water permeability of 65.7–79.6 L·m⁻¹. -2 ·h -1 The NaCl rejection rate was 82.38%–90.25%. This indicates that although changing the pH of the aqueous phase can change the water flux, without the participation of functional polyamines, the same salt rejection performance as in the examples cannot be obtained. The performance changes shown in the examples are not simply caused by the increase in pH.

[0068] In Comparative Example 9, the mass fraction of tris(2-aminoethyl)amine was 0.3 wt.%, the pH of the aqueous phase was 6.2, and the water permeation flux of the resulting membrane was 82.4 L·m. -2 ·h -1 The NaCl rejection rate was 90.52%. Under these acidic conditions, m-phenylenediamine is more prone to protonation, resulting in fewer free amine groups that can participate in interfacial polymerization and a decrease in the degree of crosslinking of the polyamide network.

[0069] In Comparative Example 10, the mass fraction of tris(2-aminoethyl)amine was 1.6 wt.%, the pH of the aqueous phase was 12.3, and the water permeation flux of the resulting membrane was 75.3 L·m. -2 ·h -1 The NaCl rejection rate was 93.58%. Under strongly alkaline conditions, the hydrolysis reaction of trimesoyl chloride increased, reducing the number of acyl chloride groups that could participate in the amidation reaction, thus affecting the formation of the polyamide network. Comparative Examples 9 and 10 show that controlling the mass fraction of tris(2-aminoethyl)amine between 0.4 wt.% and 1.5 wt.% and maintaining the pH of the aqueous phase between 7.5 and 10.5 is more conducive to balancing the water permeation flux and NaCl rejection rate of the reverse osmosis membrane.

[0070] The test results in Table 1 show that, with other interfacial polymerization conditions remaining consistent, there is a correlation between the concentration of tris(2-aminoethyl)amine and the initial pH, Zeta potential, and protonation state of the aqueous phase, further affecting the water permeation flux and NaCl rejection rate of the resulting reverse osmosis membrane. Specifically, 0.4 wt.%–0.5 wt.% of tris(2-aminoethyl)amine is beneficial for obtaining a higher NaCl rejection rate, while 0.8 wt.%–1.5 wt.% of tris(2-aminoethyl)amine is beneficial for improving the water permeation flux. The comparative results also indicate that these performance changes are not caused by simply adjusting the pH of the aqueous phase or by using triethylamine.

[0071] Test Example 2 To investigate the effects of tris(2-aminoethyl)amine concentration and its protonation state on the structure of the polyamide separation layer, polyamide reverse osmosis membranes obtained in Examples 1, 4, and 4 were selected and subjected to scanning electron microscopy, atomic force microscopy, free volume fraction simulation, and molecular weight cutoff and separation pore size tests, respectively.

[0072] like Figures 1-3 As shown, Figure 1 , Figure 2 and Figure 3 The images are scanning electron microscope images of the polyamide reverse osmosis membranes obtained in Examples 1, 4 and 4, respectively. In each image, (a) is a membrane surface morphology image and (b) is a membrane cross-sectional morphology image. The 500 nm and 200 nm values ​​in the images are the scale bars for the corresponding images. The marking lines in the cross-sectional morphology images are used to indicate the polyamide separation layer, and the numerical labels indicate the thickness of the polyamide separation layer.

[0073] The polyamide release layer obtained in Example 1 exhibited a relatively dense ridge-like morphology with a cross-sectional thickness of 205.3 ± 0.2 nm; the polyamide release layer obtained in Example 4 had a relatively smooth surface with a cross-sectional thickness of 141.5 ± 0.2 nm; and the polyamide release layer obtained in Comparative Example 4 had a cross-sectional thickness of 195.8 ± 0.3 nm, with its surface morphology and thickness falling between those of Examples 1 and 4. These results indicate that different concentrations of tris(2-aminoethyl)amine correspond to different protonation states, which in turn affect the formation process and thickness of the polyamide release layer.

[0074] like Figures 4-6 As shown, Figure 4 , Figure 5 and Figure 6The images show the surface roughness test results of the polyamide reverse osmosis membranes obtained in Examples 1, 4, and 4, respectively. The test area is 5 μm × 5 μm, and the height scale range is -150 to 250 nm. The surface roughness of the polyamide separation layer obtained in Example 1 is 56.2 ± 0.1 nm, in Example 4 it is 28.9 ± 0.2 nm, and in Comparative Example 4 it is 43.4 ± 0.2 nm. The membrane surface of Example 1 has more obvious undulations, the membrane surface of Example 4 is relatively smooth, and the roughness of Comparative Example 4 is between the two. Figures 1-3 The results shown correspond to the scanning electron microscope observations.

[0075] like Figures 7-9 As shown, Figure 7 , Figure 8 and Figure 9 The figures show simulated free volume fractions of the polyamide release layers obtained in Examples 1, 4, and 4, respectively. The colored areas in the figures represent the free volume regions within the polyamide network. Simulations show that the free volume fraction of the polyamide release layer obtained in Example 1 is 18.35%, in Example 4 it is 22.04%, and in Comparative Example 4 it is 20.03%.

[0076] The free volume fraction of Example 4 is higher than that of Example 1, indicating that its polyamide network has relatively more intermolecular free space, which can provide more transport channels for water molecules; the free volume fraction of Example 1 is relatively small, which corresponds to its denser polyamide separation layer and higher NaCl rejection rate.

[0077] like Figure 10 As shown, Figure 10 The graph shows the molecular weight cutoff and separation pore size test results of the polyamide reverse osmosis membranes obtained in Examples 1, 4, and Comparative Example 4. The fitting curves for each group are distinguished according to the legend in the graph. The molecular weight cutoff of the membrane obtained in Example 1 is 80 Da, corresponding to a separation pore size of 0.205 nm; the molecular weight cutoff of the membrane obtained in Example 4 is 98 Da, corresponding to a separation pore size of 0.234 nm; and the molecular weight cutoff of the membrane obtained in Comparative Example 4 is 85 Da, corresponding to a separation pore size of 0.219 nm.

[0078] Example 1 has a smaller separation pore size, corresponding to its higher NaCl rejection rate; Example 4 has a larger separation pore size, corresponding to its higher water permeation flux; Comparative Example 4 has a molecular weight cutoff and separation pore size that are between those of Example 1 and Example 4.

[0079] comprehensive Figures 1-10The test results show that, with other interfacial polymerization conditions remaining consistent, the thickness, surface roughness, free volume fraction, and separation pore size of the polyamide separation layer can be changed by presetting the addition concentration of tris(2-aminoethyl)amine. When tris(2-aminoethyl)amine is in the protonation enrichment dominant mode, the resulting polyamide separation layer is relatively thick, with a larger surface roughness, smaller free volume fraction, and smaller separation pore size, corresponding to a higher NaCl rejection rate. When tris(2-aminoethyl)amine is in the deprotonation crosslinking dominant mode, the resulting polyamide separation layer is relatively thin, with a smoother surface, larger free volume fraction, and larger separation pore size, corresponding to a higher water permeation flux.

[0080] 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 person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in the present invention, and these should all 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 polyamine protonated programmed polyamide reverse osmosis membrane, comprising a polysulfone ultrafiltration membrane and a polyamide separation layer formed on the surface of the polysulfone ultrafiltration membrane, characterized in that, The polyamide separation layer is formed by interfacial polymerization of an aqueous solution containing m-phenylenediamine, camphor sulfonic acid and tris(2-aminoethyl)amine and an organic solution containing trimesoyl chloride; the mass fraction of tris(2-aminoethyl)amine in the aqueous solution is 0.4 wt.% to 1.5 wt.%, the pH value of the aqueous solution is 7.5 to 10.5, and the aqueous solution does not contain any added acid-base adjusters.

2. The polyamine protonated programmed polyamide reverse osmosis membrane according to claim 1, characterized in that, The tris(2-aminoethyl)amine in the aqueous solution has a mass fraction of 0.4 wt.% to 0.5 wt.%, the pH of the aqueous solution is 7.5 to 8.5, and the tris(2-aminoethyl)amine is in a protonation enrichment-dominant mode, with an average number of the three primary amine groups in the molecule in a protonated state of not less than 2. Under test conditions of a feed solution of 2000 mg / L NaCl aqueous solution, a filtration pressure of 1.55 MPa, a temperature of 25 ± 1 ℃, and a cross-flow rate of 80 L / h, the water permeation flux of the polyamine protonated programmed polyamide reverse osmosis membrane is 51.4 to 55.7 L·m. -2 ·h -1 The NaCl retention rate is 99.08%–99.35%.

3. The polyamine protonated programmed polyamide reverse osmosis membrane according to claim 1, characterized in that, The tris(2-aminoethyl)amine in the aqueous solution has a mass fraction of 0.8 wt.% to 1.5 wt.%, the pH of the aqueous solution is 9.5 to 10.5, and the tris(2-aminoethyl)amine is in a deprotonated crosslinking mode, with an average number of the three primary amine groups in the molecule in a protonated state not exceeding 1. Under test conditions of a feed solution of 2000 mg / L NaCl aqueous solution, a filtration pressure of 1.55 MPa, a temperature of 25 ± 1 ℃, and a crossflow rate of 80 L / h, the water permeation flux of the polyamine protonated programmed polyamide reverse osmosis membrane is 64.2 to 75.1 L·m⁻¹. -2 ·h -1 The NaCl retention rate is 98.51% to 98.81%.

4. The polyamine protonated programmed polyamide reverse osmosis membrane according to any one of claims 1 to 3, characterized in that, The polyamide separation layer has a thickness of 141.5–205.3 nm, a surface roughness of 28.9–56.2 nm, a free volume fraction of 18.35%–22.04%, and a separation pore size of 0.205–0.234 nm; the polyamine protonated programmed polyamide reverse osmosis membrane has a molecular weight cutoff of 80–98 Da.

5. A method for preparing a polyamine protonated programmed polyamide reverse osmosis membrane, characterized in that, Includes the following steps: S1. Dissolve m-phenylenediamine, camphor sulfonic acid, and tris(2-aminoethyl)amine in water to prepare an aqueous solution. Control the mass fraction of tris(2-aminoethyl)amine in the aqueous solution to be 0.4 wt.% to 1.5 wt.%, and do not add any acid-base adjuster to make the pH value of the aqueous solution 7.5 to 10.

5. Preset the protonation state of the tris(2-aminoethyl)amine to different functional dominant modes. S2. The aqueous solution obtained in step S1 is poured onto the surface of the polysulfone ultrafiltration membrane, and after standing, the excess aqueous solution is removed to obtain an aqueous adsorption membrane. S3. Coat the surface of the aqueous adsorption membrane prepared in step S2 with an organic phase solution containing pyromellitic chloride, let it stand to carry out interfacial polymerization reaction, and then remove the excess organic phase solution to obtain the interfacial polymerization precursor membrane. S4. The interfacial polymerization precursor membrane obtained in step S3 is subjected to heat treatment to obtain the polyamine protonated programmed polyamide reverse osmosis membrane.

6. The method for preparing a polyamine protonated programmed polyamide reverse osmosis membrane according to claim 5, characterized in that, In step S1, the mass fraction of the tri(2-aminoethyl)amine is 0.4 wt.% to 0.5 wt.%, and the pH value of the aqueous solution is 7.5 to 8.5, so that the tri(2-aminoethyl)amine is in the protonation enrichment function-dominated mode, and the average number of the three primary amine groups in the tri(2-aminoethyl)amine molecule in the protonated state is not less than 2.

7. The method for preparing a polyamine protonated programmed polyamide reverse osmosis membrane according to claim 5, characterized in that, In step S1, the mass fraction of the tri(2-aminoethyl)amine is 0.8 wt.% to 1.5 wt.%, and the pH value of the aqueous solution is 9.5 to 10.5, so that the tri(2-aminoethyl)amine is in the deprotonated crosslinking functional dominant mode, and the average number of the three primary amine groups in the tri(2-aminoethyl)amine molecule in the protonated state is not greater than 1.

8. The method for preparing a polyamine protonated programmed polyamide reverse osmosis membrane according to claim 5, characterized in that, In step S1, the mass fraction of m-phenylenediamine in the aqueous solution is 1.5 wt.% to 2.0 wt.%, and the mass fraction of camphor sulfonic acid in the aqueous solution is 1.5 wt.% to 2.5 wt.%; in step S2, the pure water flux of the polysulfone ultrafiltration membrane at a cross-flow filtration pressure of 0.2 MPa is 150 to 180 L·m. -2 ·h -1 The membrane has a pore size of 30–60 nm and a sponge-like cross-section. The aqueous solution is allowed to stand on the surface of the polysulfone ultrafiltration membrane for 30–120 s. After removing excess aqueous solution, nitrogen gas is used to blow away the residual aqueous solution on the membrane surface.

9. The method for preparing a polyamine protonated programmed polyamide reverse osmosis membrane according to claim 5, characterized in that, In step S3, the organic phase solution uses n-hexane as a solvent, the mass fraction of the trimesoyl chloride in the organic phase solution is 0.1 wt.% to 0.15 wt.%, and the interfacial polymerization reaction time is 30 to 120 s.

10. The method for preparing a polyamine protonated programmed polyamide reverse osmosis membrane according to claim 5, characterized in that, In step S4, the heat treatment temperature is 80–120 °C and the heat treatment time is 180–300 s; after the heat treatment is completed, the resulting membrane is cooled, rinsed with deionized water and dried.

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