A composite nanofiltration membrane, its preparation method, and its application in phosphoric acid purification and refining.

Abstract

This invention belongs to the field of nanofiltration membrane preparation technology, specifically a nanofiltration composite gel membrane, its preparation method, and its application in phosphoric acid purification and refining. A polymer selective separation layer is deposited onto the surface of a base membrane via interfacial polymerization. The resulting composite membrane is then activated in an activation solvent at 30–100°C to obtain the composite nanofiltration membrane. The activation solvent is a poor solvent used for the deposition of the polymer selective separation layer and for the base membrane. This invention, through high-temperature solvent activation, intensifies the interaction between the selective separation layer and the base membrane, promoting a more regular pore arrangement in the selective separation layer, thereby significantly improving membrane flux and selective permeation capacity for phosphoric acid. This invention is low-cost, simple, and suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, and particularly relates to a composite nanofiltration membrane, its preparation method, and its application in phosphoric acid purification and refining. Background Technology

[0002] Phosphorus, a valuable element, is widely used in agriculture, chemical industry, and pharmaceuticals. However, phosphorus emissions often cause pollution problems such as eutrophication of water bodies, resulting in economic and property losses. Therefore, phosphorus resource recovery has both environmental and economic value and is an effective means of addressing phosphorus resource scarcity.

[0003] Nanofiltration membranes are tools that utilize pore size and charge to retain substances. Due to their selective permeability, they are often used in the selective purification of certain high-value elements. Therefore, the application of nanofiltration membranes for the purification and selective separation of phosphoric acid has strong application prospects. Polyamide nanofiltration membranes have become the most successful nanofiltration membranes in industrial applications due to their simple preparation process, small pore size, high water permeation flux, and strong antifouling properties. Interfacial polymerization is often used to prepare polyamide nanofiltration membranes. During interfacial polymerization, aqueous monomers such as m-phenylenediamine (MPD) and piperazine (PIP) react with 1,3,5-benzenetricarboxylic acid chloride (TMC) to form a polyamide selective layer on the surface of the polymer ultrafiltration membrane, ultimately resulting in a denser ultrafiltration or nanofiltration membrane. Generally, the membrane obtained by this method includes a nonwoven fabric, an ultrafiltration base membrane layer, and a polyamide separation layer. However, because nanofiltration membranes used for phosphoric acid separation and purification require larger pore sizes and higher charges, existing ultrafiltration membranes on the market are difficult to apply to the selective purification of phosphoric acid, resulting in problems with low flux and selectivity. Therefore, it is necessary to improve upon the current interfacial polymerization method for preparing composite nanofiltration membranes in order to overcome the existing problems of poor flux and retention. Summary of the Invention

[0004] The purpose of this invention is to provide a composite nanofiltration membrane, its preparation method, and its application in phosphoric acid purification and refining, so as to improve the flux and selective separation and purification capabilities of the nanofiltration membrane.

[0005] To achieve the above objectives, the first aspect of the present invention provides a method for preparing a composite nanofiltration membrane, comprising: depositing a polymer selective separation layer onto the surface of a base membrane by interfacial polymerization, and then performing solvent activation treatment on the resulting composite membrane in an activation solvent at 30–100°C to obtain a composite nanofiltration membrane; wherein the activation solvent is a poor solvent for the polymer selective separation layer and the base membrane.

[0006] That is, a solvent that will not cause the polymer separation layer and the base film to dissolve is selected as the activation solvent.

[0007] Furthermore, the solvent activation treatment includes: immersing the composite membrane in the activation solvent at 30-100°C for 1-10 minutes, preferably 3-10 minutes, and then immersing it in the replacement solvent for 1-10 minutes to remove the activation solvent;

[0008] The preferred temperature of the activation solvent is 40–100°C, and the preferred activation time is 5 min.

[0009] Furthermore, the activating solvent includes a first organic solvent or a mixed solvent consisting of a first organic solvent and water, wherein the first organic solvent includes one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone. The volume ratio of the first organic solvent to water is 100:(0-10).

[0010] The displacement solvent includes water and / or a second organic solvent, the second organic solvent including one or more of ethanol, methanol, isopropanol, glycerol and tetrahydrofuran.

[0011] Furthermore, the polymer selective separation layer is a polyamide selective separation layer.

[0012] Furthermore, the composite membrane is prepared by forming a separation layer on the surface of the base membrane through interfacial polymerization between an aqueous solution and an oil solution.

[0013] Furthermore, the interfacial polymerization includes: immersing the base film in an aqueous solution, then removing it and immersing it in an oil solution, then removing it and heat-treating it to obtain a composite film with a polymer selective separation layer deposited on the surface.

[0014] Furthermore, the interfacial polymerization includes: immersing the base film in an aqueous solution for 1-10 min, then removing it and drying the surface for 1-10 min, then immersing it in an oil solution for 1-10 min, and then removing it for heat treatment to obtain a composite film with a polymer selective separation layer deposited on the surface.

[0015] The aqueous solution contains amine monomers, preferably binary or polyamines, and the oil solution contains acyl chloride monomers, preferably binary or polyacyl chlorides.

[0016] Furthermore, the amine monomers include one or more of m-phenylenediamine, piperazine, branched polyethyleneimine, 2-methylpiperazine, 4-aminomethylpiperazine, 1,3-diaminocyclohexane or 1,4-diaminocyclohexane, p-phenylenediamine, pyromellitic triamine, propylenediamine, phenylenedimethyldiamine, and 2,5-dimethylpiperazine; preferably m-phenylenediamine, piperazine, or branched polyethyleneimine with a molecular weight of 6000-70000 Da; more preferably branched polyethyleneimine with a molecular weight of 6000-70000 Da, with the following structural formula. When branched polyethyleneimine is used and activated by a high-temperature solvent, the resulting composite nanofiltration membrane exhibits a significantly better separation ratio for phosphoric acid compared to other amine monomers.

[0017]

[0018] The acyl chloride monomers include one or more of the following: pyromellitic triacyl chloride, pentyl triacyl chloride, maleic diacyl chloride, terephthaloyl chloride, biphenyl diacyl chloride, benzenetrisulfonyl chloride, isophthaloyl chloride, cyclopentanetriacyl chloride, propyltriacyl chloride, glutaryl chloride, succinic triacyl chloride, adipic acid chloride, cyclopropanetriacyl chloride, cyclobutanetriacyl chloride, cyclobutanetetraacyl chloride, cyclopentanediacyl chloride, cyclopentanetetraacyl chloride, cyclohexanediacyl chloride, cyclohexanetriacyl chloride, and cyclohexanetetraacyl chloride.

[0019] Furthermore, the aqueous solution also includes an acid-base regulator and a surfactant. The surfactant is preferably sodium dodecyl sulfonate. The alkali regulator is one of sodium hydroxide, ammonia, triethylamine, or potassium hydroxide. The acid regulator is one of camphor sulfonic acid, oxalic acid, or formic acid. The concentration of the surfactant is 0.0–0.07 wt%, the concentration of the alkali regulator is 0–2 wt%, and the concentration of the acid regulator is 0–3 wt%.

[0020] Furthermore, the heat treatment temperature is 50–60°C, and the heat treatment time is 10–20 min.

[0021] Furthermore, the concentration of amine monomers in the aqueous solution is 0.5–5.0 wt%; and the concentration of acyl chloride monomers in the oil solution is 0.01–4.0 wt%.

[0022] Furthermore, the solvent of the aqueous phase solution is water, and the solvent of the oil phase solution is one or more of n-hexane, isoparaffin solvents (e.g., Isopar-G, Isopar-L, or Isopar-E).

[0023] Furthermore, the base membrane is made of one or more of poly(p-phenylene terephthalamide) (Kevlar), polypropylene (PP), polyethylene (PE), and poly(m-phenylene isophthalamide) (Nomex), preferably poly(p-phenylene terephthalamide). The base membrane is an ultrafiltration membrane.

[0024] Furthermore, when the base film is made of poly(p-phenylene terephthalamide), the base film is prepared by a phase inversion method, specifically including: coating a poly(p-phenylene terephthalamide) solution with a concentration of 1.5-2.0 wt% onto a nonwoven support layer, and then placing it in a coagulation bath for phase inversion to obtain a gel base film; the coating thickness is 150-250 μm.

[0025] The solvent of the coagulation bath is water or a mixture of water and a water-soluble organic solvent, wherein the volume ratio of water to water-soluble organic solvent is 100:(1-10); the water-soluble organic solvent includes one or more of sulfolane, N,N-dimethylformamide, diphenyl sulfone, dimethylacetamide, N-methylpyrrolidone, phenol, hexamethylphosphoric triamine, and 1,3-dimethyl-2-imidazolinone.

[0026] This process involves first using a solvent-resistant gel membrane as a base membrane, and then depositing a polymer selective separation layer onto the surface of the base membrane via interfacial polymerization to obtain a nanofiltration composite gel membrane. The resulting interfacially polymerized composite gel membrane is then subjected to high-temperature solvent activation post-treatment to obtain a nanofiltration composite gel membrane with highly efficient phosphoric acid purification capabilities. The interfacially polymerized composite gel membrane is formed by interfacial polymerization on a solvent-resistant gel base membrane, and consists of a polymer selective separation layer formed through interfacial polymerization and a gel base membrane.

[0027] Furthermore, the interfacial polymerization includes: pouring an aqueous solution containing 2 wt% m-phenylenediamine and 0.05 wt% sodium dodecyl sulfonate onto the surface of the poly(p-phenylenediamine) terephthalamide gel membrane, allowing it to stand for 5 min, pouring out the aqueous solution, drying the surface, pouring in an oil solution containing 0.15 wt% acyl chloride monomer, reacting for 1 min, pouring out the surface oil solution, and after the surface is air-dried, heat-treating at 50–60°C for 10–20 min.

[0028] A second aspect of the present invention provides a composite nanofiltration membrane, which is obtained by any of the preparation methods described above.

[0029] A third aspect of the present invention provides an application of a composite nanofiltration membrane, wherein the composite nanofiltration membrane is used for the separation, purification and refining of phosphoric acid.

[0030] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0031] 1. The method for preparing the composite nanofiltration membrane provided by the present invention promotes the interaction between the polymer selective separation layer and the base membrane through high-temperature solvent activation, optimizes the pore size and surface charge of the surface selective layer, and makes the pore arrangement of the polymer selective separation layer more regular, thereby obtaining a high-flux composite nanofiltration membrane and improving the selective separation and purification capacity of the composite nanofiltration membrane for phosphoric acid.

[0032] 2. This invention uses a gel ultrafiltration membrane as the base membrane, prepares a gel composite membrane through interfacial polymerization, and then combines it with high-temperature solvent activation treatment. By utilizing the interaction between the gel base layer and the polyamide selective separation layer, a nanofiltration composite gel membrane with high-efficiency phosphoric acid purification capability is obtained.

[0033] 3. By adjusting the types and concentrations of aqueous and oil phase monomers, this invention can improve the phosphoric acid selective purification performance of interfacial polymerization composite nanofiltration membranes to a certain extent. When polyethyleneimine is used as an amine monomer, the resulting composite nanofiltration membrane has a better separation and purification capacity for phosphoric acid under the activation of high-temperature solvent.

[0034] 4. The composite nanofiltration membrane obtained by this invention has high flux, high retention, and high selective retention of single or multivalent ions. Compared with traditional preparation methods, its performance is significantly improved. Moreover, this method is simple, easy to prepare, and uses inexpensive raw materials, making it highly practical for industrial applications. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0036] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0037] The performance testing method for the composite nanofiltration membrane of this invention is as follows:

[0038] The water flux of a composite nanofiltration membrane is measured by the volume of water V per unit time t and per unit membrane area S, controlled by a unit transmembrane pressure difference P. When using a cross-flow filtration device operating at a constant pressure, its water flux is calculated using the following formula:

[0039] J = V / (StP)

[0040] In the following examples and comparative examples, the unit of water flux is L / (bar.m). 2 .h).

[0041] The separation membrane retention performance test defines retention capacity as the ability to prevent or retain a specific type of substance in a solution. The retention rate is calculated using the following formula: the concentration C1 of a specific substance in the feed solution and the concentration C2 of a specific substance in the effluent solution are used to determine the retention rate.

[0042] R = (C1 - C2) / C1 × 100%.

[0043] This invention tested the filtration performance of composite nanofiltration membranes with and without high-temperature activation, without heating activation, and with heating activation. The raw material solutions were deionized aqueous solutions containing 2.0 g / L of sodium chloride, sodium sulfate, magnesium sulfate, and magnesium chloride, respectively; cross-flow filtration was used, and the tests were conducted at room temperature and 5 bar.

[0044] Simultaneously, the selective separation performance of the membrane for phosphoric acid was evaluated using a mixed solution (containing 2.0 g / L magnesium sulfate and 3.36 g / L phosphoric acid), where R1 is the magnesium ion rejection rate in the mixed solution, and R2 is the phosphoric acid rejection rate of the membrane. The phosphoric acid separation ratio was calculated using the following formula:

[0045] S = (1-R2) / (1-R1).

[0046] Comparative Example 1

[0047] (1) By dissolving 4g of poly(m-phenylene isophthalamide) in a mixture of 6g of 50wt% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0048] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 250 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0049] (3) Immerse the gel ultrafiltration membrane in a 3 wt% m-phenylenediamine solution for 5 min, blow dry the surface for 3 min, then immerse the membrane in a 0.15 wt% hexane solution of benzotrimethylammonium chloride for 1 min, and take it out and treat it at 60℃ for 15 min.

[0050] (5) Place the composite gel membrane from step (3) in DMSO (dimethyl sulfoxide) solution at room temperature for 5, 10 and 20 min respectively to obtain nanofiltration composite gel membrane. After completion, place it in deionized water solution to terminate the reaction.

[0051] Table 1 shows the flux, rejection rate, and flux increase rate relative to the unactivated composite membrane obtained in Comparative Example 1 for several salts.

[0052]

[0053] It can be seen that solvent activation has little effect on salt rejection, but it can increase throughput.

[0054] Example 1

[0055] (1) By dissolving 4g of poly(p-phenylene terephthalamide) (PPTA) in a mixture of 6g of 50% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0056] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 200 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0057] (3) Immerse the gel ultrafiltration membrane in a solution containing 3 wt% m-phenylenediamine and 0.05 wt% sodium dodecyl sulfonate for 5 min, blow dry the surface for 3 min, then immerse the membrane in a hexane solution containing 0.15 wt% benzotrimethylammonium chloride for 1 min, and take it out and treat it at 60℃ for 15 min.

[0058] (5) Place the composite gel membrane from step (3) in a DMSO solution at 60°C for 5, 10, and 20 min to obtain a nanofiltration composite gel membrane. After completion, place it in a deionized water solution to terminate the reaction.

[0059] Table 2 shows the flux, rejection rate, and flux increase relative to the unactivated composite membrane of the nanofiltration gel composite membrane obtained in Example 1 for several salts.

[0060]

[0061] It can be seen that when the solvation treatment is carried out at elevated temperature, the flux of the resulting nanofiltration gel composite membrane is significantly improved compared with that of the room temperature solvent activation treatment.

[0062] Comparative Example 2

[0063] (1) By dissolving 4g of poly(p-phenylene terephthalamide) (PPTA) in a mixture of 6g of 50% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0064] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 200 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0065] (3) Immerse the gel ultrafiltration membrane in a solution of 3 wt% m-phenylenediamine and 0.05 wt% sodium dodecyl sulfonate for 5 min, dry the surface for 3 min, then immerse the membrane in a solution of 0.15 wt% benzotrimethylammonium chloride in hexane for 1 min, and then treat it at 60℃ for 15 min.

[0066] (5) Place the composite gel membrane from step (3) in DMSO solution at room temperature (25℃) for 5, 10 and 20 min respectively to obtain nanofiltration composite gel membrane. After completion, place it in deionized water solution to terminate the reaction.

[0067] Table 3 shows the flux, rejection rate, and flux increase relative to the unactivated composite membrane of the nanofiltration gel composite membrane obtained in Comparative Example 2 for several salts.

[0068]

[0069]

[0070] Compared to Comparative Example 1, the flux increase was more significant when poly(p-phenylene terephthalamide) was used as the base membrane. The flux was lower at room temperature compared to the temperature-activated treatment.

[0071] Example 2

[0072] (1) By dissolving 4g of poly(p-phenylene terephthalamide) (PPTA) in a mixture of 6g of 50% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0073] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 200 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0074] (3) Immerse the gel ultrafiltration membrane in a solution of 3 wt% m-phenylenediamine and 0.05 wt% sodium dodecyl sulfonate for 5 min, dry the surface for 3 min, then immerse the membrane in a solution of 0.15 wt% benzotrimethylammonium chloride in hexane for 1 min, and then treat it at 60℃ for 15 min.

[0075] (5) The composite gel membrane from step (3) was placed in a 60°C N-methylpyrrolidone solution for 5, 10, and 20 min to obtain a nanofiltration composite gel membrane. After completion, the reaction was terminated by placing it in a deionized water solution.

[0076] Table 4 shows the flux, rejection rate, and flux increase rate relative to the unactivated composite membrane of the nanofiltration gel composite membrane obtained in Example 2 for several salts.

[0077]

[0078]

[0079] It can be seen that, compared with Example 1, the flux decreased when the activation solvent was changed, indicating that the activation solvent has an important influence on the pore structure of the polyamide separation layer.

[0080] Comparative Example 3

[0081] (1) By dissolving 4g of poly(p-phenylene terephthalamide) (PPTA) in a mixture of 6g of 50% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0082] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 200 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0083] (3) Immerse the gel ultrafiltration membrane in a solution of 3 wt% m-phenylenediamine and 0.05 wt% sodium dodecyl sulfonate for 5 min, dry the surface for 3 min, then immerse the membrane in a solution of 0.15 wt% benzotrimethylammonium chloride in hexane for 1 min, and then treat it at 60℃ for 15 min.

[0084] (5) Place the composite gel membrane from step (3) in a room temperature (25℃) N,N-dimethylformamide solution for 5, 10, and 20 min respectively to obtain a nanofiltration composite gel membrane. After completion, place it in a deionized water solution to terminate the reaction.

[0085] Table 5 shows the flux, rejection rate, and flux increase rate relative to the unactivated composite membrane of the nanofiltration gel composite membrane obtained in Comparative Example 3 for several salts.

[0086]

[0087]

[0088] Example 3

[0089] (1) By dissolving 4g of poly(p-phenylene terephthalamide) (PPTA) in a mixture of 6g of 50% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0090] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 200 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0091] (3) Immerse the gel ultrafiltration membrane in a solution of 3 wt% m-phenylenediamine and 0.05 wt% sodium dodecyl sulfonate for 5 min, dry the surface for 3 min, then immerse the membrane in a solution of 0.15 wt% benzotrimethylammonium chloride in hexane for 1 min, and then treat it at 60℃ for 15 min.

[0092] (5) The composite gel membrane from step (3) was placed in N,N-dimethylformamide solution at 60℃ for 5, 10 and 20 min to obtain nanofiltration composite gel membrane. After completion, the reaction was terminated by placing it in deionized water solution.

[0093] Table 6 shows the flux, rejection rate, and flux increase relative to the unactivated composite membrane of the nanofiltration gel composite membrane obtained in Example 3 for several salts.

[0094]

[0095]

[0096] Comparative Example 4

[0097] (1) By dissolving 4g of poly(p-phenylene terephthalamide) (PPTA) in a mixture of 6g of 50% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0098] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 200 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0099] (3) Immerse the gel ultrafiltration membrane in a solution of 3 wt% m-phenylenediamine and 0.05 wt% sodium dodecyl sulfonate for 5 min, dry the surface for 3 min, then immerse the membrane in a solution of 0.15 wt% benzotrimethylammonium chloride in hexane for 1 min, and then treat it at 60℃ for 15 min.

[0100] (5) Place the composite gel membrane from step (3) in a DMF solution at room temperature (25°C) for 5, 10, and 20 min to obtain a nanofiltration composite gel membrane. After completion, place it in a deionized water solution to terminate the reaction.

[0101] Table 7 shows the flux, rejection rate, and flux increase relative to the unactivated composite membrane obtained in Comparative Example 4 for several salts.

[0102]

[0103] Example 4

[0104] (1) By dissolving 4g of poly(p-phenylene terephthalamide) (PPTA) in a mixture of 6g of 50% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0105] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 200 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0106] (3) Immerse the gel ultrafiltration membrane in a solution of 3 wt% m-phenylenediamine and 0.05 wt% sodium dodecyl sulfonate for 5 min, dry the surface for 3 min, then immerse the membrane in a solution of 0.15 wt% benzotrimethylammonium chloride in hexane for 1 min, and then treat it at 60℃ for 15 min.

[0107] (5) The composite gel membrane from step (3) was placed in a dimethyl sulfoxide solution at 50°C for 5, 10 and 20 min to obtain a nanofiltration composite gel membrane. After completion, the reaction was terminated by placing it in a deionized water solution.

[0108] Table 8 shows the flux, rejection rate, and flux increase relative to the unactivated composite membrane of the nanofiltration gel composite membrane obtained in Example 4 for several salts.

[0109]

[0110] Example 5

[0111] (1) By dissolving 4g of poly(p-phenylene terephthalamide) (PPTA) in a mixture of 6g of 50% potassium hydroxide solution and 190g of dimethyl sulfoxide, and heating and stirring at 35°C for 48h, a Kevlar fiber casting solution with a concentration of 2wt% was obtained.

[0112] (2) The casting solution was scraped onto the nonwoven fabric with a thickness of 200 μm using a scraper. The nonwoven fabric loaded with Kevlar casting solution was then immersed in deionized water. After phase inversion for 2 min, a gel ultrafiltration membrane was formed.

[0113] (3) Immerse the gel ultrafiltration membrane in an aqueous solution of 3 wt% m-phenylenediamine, 0.05 wt% sodium dodecyl sulfonate and 0.01 wt% sodium hydroxide for 5 min, dry the surface for 3 min, then immerse the membrane in a hexane solution of 0.15 wt% benzotrimethylammonium chloride for 1 min, and treat it at 60℃ for 15 min.

[0114] (5) Place the composite gel membrane from step (3) in an N,N-dimethylformamide solution at 60°C for 5, 10, and 20 min to obtain a nanofiltration composite gel membrane. After completion, place it in a deionized water solution to terminate the reaction.

[0115] Table 9 shows the flux, rejection rate, and flux increase relative to the unactivated composite membrane of the nanofiltration gel composite membrane obtained in Example 5 for several salts.

[0116]

[0117] Example 6

[0118] (1) Immerse a commercial polypropylene membrane (molecular weight cutoff 50kDa, DuPont) in a m-phenylenediamine solution for 5 min, blow dry the surface for 3 min, then immerse the membrane in a hexane solution of 0.15wt% benzotrimethylammonium chloride for 1 min, and treat at 60℃ for 15 min.

[0119] (2) The composite gel membrane from step (1) was placed in N,N-dimethylformamide solution at 60℃ for 5, 10 and 20 min respectively to obtain nanofiltration composite gel membrane. After completion, the reaction was terminated by placing it in deionized water solution.

[0120] Table 10 shows the flux, rejection rate, and flux increase relative to the unactivated composite membrane obtained in Example 6 for several salts.

[0121]

[0122]

[0123] Example 7

[0124] (1) Immerse the commercial polyethylene film (molecular weight cutoff 50kDa, DuPont) in m-phenylenediamine solution for 5 min, blow dry the surface for 3 min, then immerse the film in n-hexane solution of 0.15wt% benzotricarboxylic acid chloride for 1 min, and treat at 60℃ for 15 min.

[0125] (2) The composite gel membrane from step (1) was placed in N,N-dimethylformamide solution at 60℃ for 5, 10 and 20 min to obtain nanofiltration composite gel membrane. After completion, the reaction was terminated by placing it in deionized water solution.

[0126] Table 11 shows the flux, rejection rate, and flux increase relative to the unactivated composite membrane obtained in Example 7 for several salts.

[0127]

[0128] Example 8

[0129] (1) Immerse the commercial polyethylene film (molecular weight cutoff 50kDa, Cypreet) in piperazine solution for 5min, blow dry the surface for 3min, then immerse the film in hexane solution of 0.15wt% benzotrimethylol chloride for 1min, and treat at 60℃ for 15min.

[0130] (2) The composite gel membrane from step (1) was placed in a dimethyl sulfoxide solution at 60°C for 5, 10, and 20 min to obtain nanofiltration composite gel membranes. After completion, the reaction was terminated by placing the membrane in a deionized water solution. Table 12 shows the flux, rejection rate, and flux increase rate relative to the unactivated composite membrane of the composite nanofiltration membrane obtained in Example 8 for several salts.

[0131]

[0132] Example 9

[0133] (1) Immerse a commercial polyethylene film (molecular weight cutoff 50kDa, Cypreet) in a branched polyethyleneimine (molecular weight 10000Da) solution for 5 min, blow dry the surface for 3 min, then immerse the film in a hexane solution of 0.15wt% benzotrimethylammonium chloride for 1 min, and treat at 60℃ for 15 min.

[0134] (2) The composite gel membrane from step (1) was placed in a dimethyl sulfoxide solution at 60°C for 5, 10, and 20 min to obtain nanofiltration composite gel membranes. After completion, the reaction was terminated by placing the membrane in a deionized water solution. Table 13 shows the flux, rejection rate, and flux increase rate relative to the unactivated composite membrane of the composite nanofiltration membrane obtained in Example 9 for several salts.

[0135]

[0136]

[0137] Example 10

[0138] (1) The polypropylene membrane (molecular weight cutoff 50kDa, Cyprete) was immersed in a 2wt% aqueous solution of branched polyethyleneimine (molecular weight 70kDa) for 4 min. After drying the surface water droplets, it was immersed in a 1.5wt% solution of tribenzoyl chloride for 4 min. Then it was dried in an oven at 60℃ for 15 min to obtain a composite nanofiltration membrane.

[0139] (2) The membranes obtained in step (1) were immersed in dimethyl sulfoxide at 60°C for 5 min, 10 min, and 20 min respectively to obtain different nanofiltration gel composite membranes. Finally, these membranes were immersed in water. Table 14 shows the flux, rejection rate, and flux improvement rate of the composite nanofiltration membranes obtained in Example 10 for several salts compared to the unactivated composite membrane.

[0140]

[0141] Example 11

[0142] (1) Immerse the nylon membrane (molecular weight cutoff 100kDa, Cyprete) in 0.25wt% of 70kDa branched polyethyleneimine aqueous solution for 4min, dry the surface water droplets, immerse it in 1.5wt% tribenzoyl chloride solution for 4min, and then treat it in an oven at 60℃ for 15min to obtain a positive valence composite nanofiltration membrane.

[0143] (2) The membranes obtained in step (1) were immersed in dimethyl sulfoxide at 60°C for 5 min, 10 min, and 20 min respectively to obtain different nanofiltration gel composite membranes. Finally, these membranes were immersed in water. Table 15 shows the flux, rejection rate, and flux improvement rate of the composite nanofiltration membranes obtained in Example 11 for several salts compared to the unactivated composite membrane.

[0144]

[0145] It can be seen that while the flux of the resulting composite nanofiltration membrane is only slightly improved when branched polyethyleneimine is used, its selective separation capability for phosphoric acid is significantly enhanced. This demonstrates that branching of polyethyleneimine combined with high-temperature solvent activation plays a crucial role in the selective separation of phosphoric acid.

[0146] Example 12

[0147] (1) Using a film scraper, the p-phenylenediamine terephthalate casting solution is scraped onto the non-woven fabric. The thickness of the scraper is 250 μm. The scraped non-woven fabric is then immersed in deionized water and left to stand for 2 minutes to form a p-phenylenediamine terephthalate-based film.

[0148] (3) The gel membrane was immersed in a 0.25wt% aqueous solution of 70kDa branched polyethyleneimine for 4 min. After drying the surface water droplets, it was immersed in a 1.5wt% solution of tribenzoyl chloride for 4 min. Then it was dried in an oven at 60℃ for 15 min to obtain a positive-valence composite nanofiltration membrane.

[0149] (4) The membranes obtained in step (3) were immersed in dimethyl sulfoxide at 30°C for 5 min, 10 min, and 20 min respectively to obtain different nanofiltration gel composite membranes. Finally, these membranes were immersed in water. Table 16 shows the flux, rejection rate, and flux improvement rate of the nanofiltration gel composite membranes obtained in Example 12 for several salts compared to the unactivated composite membrane.

[0150]

[0151] The flux of the activated membranes increased dramatically, with an increase in the rejection of magnesium chloride and a decrease in the rejection of monovalent ions.

[0152] The same testing conditions were applied to commercially available Dow NF270 and NF90 nanofiltration membranes, and the flux and retention data of the salt solution were obtained as shown in Table 19. Table 19 shows that the nanofiltration composite membrane of the present invention (the membrane activated for 20 min in Example 11 is membrane 1 of the present invention, and the membrane activated for 20 min in Example 12 is membrane 2 of the present invention) has stronger advantages over traditional NF270 and NF90 in terms of retention efficiency, high-valent cation retention (magnesium chloride), and magnesium-phosphorus separation, indicating that the preparation method of the present invention has broader application prospects.

[0153] Table 17 Performance Comparison between Dow's commercial membranes NF90 and NF270 and the nanofiltration gel composite membrane of this invention

[0154]

[0155] In summary, the present invention provides a high-performance nanofiltration composite gel membrane for phosphoric acid purification and refining. Under the action of high-temperature solvent, the interaction between the selective layer and the substrate layer is more intense, which promotes a more regular arrangement of the pores in the membrane selective separation layer. Therefore, the gel nanofiltration composite membrane prepared by this method has a high flux and a strong phosphoric acid purification capacity. Furthermore, the method is simple, easy to prepare, and uses inexpensive raw materials, making it highly practical for industrial applications.

[0156] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An application of a composite nanofiltration membrane, characterized in that, The composite nanofiltration membrane is used for the separation, purification, and refining of phosphoric acid. The preparation method of the composite nanofiltration membrane includes: depositing a polymer selective separation layer onto the surface of a base membrane through interfacial polymerization, and then activating the resulting composite membrane in an activation solvent at 40~100 °C to obtain the composite nanofiltration membrane; the activation solvent is a poor solvent for both the polymer selective separation layer and the base membrane. The interfacial polymerization includes: wetting the base film in an aqueous solution, then removing it and wetting it again in an oil solution, then removing it and heat-treating it to obtain a composite film with a polymer selective separation layer deposited on the surface; The aqueous solution includes amine monomers, and the oil solution includes acyl chloride monomers; the amine monomers are branched polyethyleneimine with a molecular weight of 6000~70000 Da.

2. The application of the composite nanofiltration membrane according to claim 1, characterized in that, The solvent activation treatment includes: immersing the composite membrane in the activation solvent for 1-10 min, and then immersing it in the replacement solvent for 3-10 min to remove the activation solvent.

3. The application of the composite nanofiltration membrane according to claim 2, characterized in that, The activating solvent is a first organic solvent, or a mixed solvent composed of a first organic solvent and water, wherein the first organic solvent includes one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N-methylpyrrolidone; The replacement solvent is water and / or a second organic solvent, wherein the second organic solvent is one or more of ethanol, methanol, isopropanol, glycerol, and tetrahydrofuran.

4. The application of the composite nanofiltration membrane according to claim 1, characterized in that, The acyl chloride monomers include one or more of the following: pyromellitic triacyl chloride, pentyl triacyl chloride, maleic diacyl chloride, terephthaloyl chloride, biphenyl diacyl chloride, benzenetrisulfonyl chloride, isophthaloyl chloride, cyclopentanetriacyl chloride, propyltriacyl chloride, glutaryl chloride, succinic triacyl chloride, adipic acid chloride, cyclopropanetriacyl chloride, cyclobutanetriacyl chloride, cyclobutanetetraacyl chloride, cyclopentanediacyl chloride, cyclopentanetetraacyl chloride, cyclohexanediacyl chloride, cyclohexanetriacyl chloride, and cyclohexanetetraacyl chloride.

5. The application of the composite nanofiltration membrane according to claim 1, characterized in that, The heat treatment temperature is 50~60℃, and the heat treatment time is 10~20 min; And / or, the concentration of amine monomers in the aqueous phase solution is 0.5~5.0 wt%; the concentration of acyl chloride monomers in the oil phase solution is 0.01~4.0 wt%. And / or, the solvent of the aqueous phase solution is water, and the solvent of the oil phase solution is one or more of n-hexane and isoparaffin solvents.

6. The application of the composite nanofiltration membrane according to claim 1, characterized in that, The base film is made of one or more of the following materials: poly(p-phenylene terephthalamide), polypropylene, polyethylene, and poly(m-phenylene isophthalamide).

7. The application of the composite nanofiltration membrane according to claim 6, characterized in that, When the base film is made of poly(p-phenylene terephthalamide), the base film is prepared by a phase inversion method, specifically including: coating a poly(p-phenylene terephthalamide) solution with a concentration of 1.5~2.0 wt% onto a non-woven fabric support layer, and then placing it in a coagulation bath for phase inversion to obtain a gel base film; The solvent of the coagulation bath is water or a mixture of water and a water-soluble organic solvent; the water-soluble organic solvent includes one or more of sulfolane, N,N-dimethylformamide, diphenyl sulfone, dimethylacetamide, N-methylpyrrolidone, phenol, hexamethylphosphoric triamine, and 1,3-dimethyl-2-imidazolinone.

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