A method of making high flux polyamide composite membranes

Abstract

The present application relates to a kind of preparation high-flux polyamide composite membrane method, belong to nanocomposite membrane design and preparation field.It includes porous support layer and separation layer, separation layer is formed by the interfacial polymerization of aqueous phase amine monomer and organic phase acyl chloride monomer, while adding sodium tetraphenylborate in aqueous phase, adding organic potassium salt in organic phase, utilize sodium tetraphenylborate and organic potassium salt at interface with polyamide layer Synchronous formation potassium tetraphenylborate nanoparticles, then utilize acetone to dissolve nanoparticle, finally form with non-through cavity structure in the inside and surface of separation layer, obtain with high-flux and high salt retention rate polyamide composite membrane.This method nanoparticle is formed synchronously with polyamide separation layer, the cavity structure formed finally can be evenly distributed in the inside of entire polyamide separation layer, and the effective thickness of polyamide separation layer is thinned.Polyamide composite membrane with cavity structure can be increased by more than one time permeation flux.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a method for preparing high-throughput polyamide composite membranes. Background Technology

[0002] Polyamide composite membranes are important separation materials widely used in water treatment, biomedicine, and food processing. The separation performance of polyamide composite membranes is mainly affected by factors such as membrane pore size, charge, and effective separation layer thickness. Polyamide composite membranes are divided into polyamide nanofiltration membranes and polyamide reverse osmosis membranes, with no clear boundary between the two. Reverse osmosis membranes generally have a pore size below 0.5 nm, while nanofiltration membranes fall between ultrafiltration and reverse osmosis membranes, with a pore size of 0.5–2.0 nm, effectively retaining organic matter with a molecular weight above 200 Da and high-valent salts. The preparation processes for reverse osmosis and nanofiltration membranes are the same, differing only in the type of monomer in the aqueous phase. Nanofiltration membranes typically use saturated amine monomers in the aqueous phase, while reverse osmosis membranes use aromatic amine monomers. Traditional preparation methods suffer from problems such as a large separation layer thickness and low permeability, limiting the application performance and efficiency of polyamide composite membranes.

[0003] Currently, reducing the thickness of the polyamide separation layer is generally considered an important way to reduce permeation resistance. However, while reducing the concentration of monomers in the aqueous or organic phases can reduce the thickness of the polyamide separation layer to some extent, it also affects the degree of crosslinking, density, surface charge, and long-term stability of the separation layer, making it difficult to achieve ideal results. Adding nanoparticle fillers to the aqueous or organic phases, utilizing the pore structure of the nanoparticles themselves or the gaps between the nanoparticles and the polyamide separation layer as water mass transfer channels, can increase the membrane permeation flux to some extent. However, directly adding nanoparticle fillers easily causes agglomeration on the upper or lower surface of the polyamide separation layer, forming defects and making it difficult to incorporate into the interior of the polyamide separation layer, thus limiting its effectiveness. Chinese invention patent document CN112316753A discloses a method for preparing a porous hollow fiber polyamide composite membrane. It utilizes the byproduct HCl from interfacial polymerization to react in situ with silver salts added to the aqueous phase to form AgCl nanoparticles, which are then dissolved to form cavities. This provides a method for forming cavities in situ within the polyamide separation layer, improving membrane permeation performance. However, one of the reactants for nanoparticles is HCl, a byproduct of interfacial polymerization. Its yield is low and its content is uncontrollable, limiting both the total amount of nanoparticles generated and their formation rate. Furthermore, interfacial polymerization is self-limiting; initially, the reaction rate is high, resulting in a large amount of HCl production and ultimately more AgCl nanoparticles and cavities, leading to a certain degree of decrease in the retention rate. As the reaction progresses, the polymerization rate gradually decreases, resulting in less HCl production and consequently fewer AgCl nanoparticles and cavities. This leads to an uneven distribution of nanocavities within the final polyamide composite film, which is detrimental to improving the overall performance of the polyamide composite film. In short, the method of generating nanoparticles using the interfacial polymer HCl cannot achieve uniform, stable, and controllable generation of nanoparticles and internal cavities, and may cause a certain degree of decrease in the retention rate. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-throughput polyamide composite membranes by forming a uniform, stable and controllable cavity structure in the interface layer to reduce the effective thickness of the separation layer while maintaining the selectivity of the polyamide composite membrane.

[0005] The technical solution of the present invention is a method for preparing a high-throughput polyamide composite membrane, comprising the following steps:

[0006] (1) Dissolve the amine monomer, surfactant, and sodium tetraphenylborate in water to obtain an aqueous solution;

[0007] (2) Dissolve the acyl chloride monomer and the organic potassium salt in an organic solvent to obtain an organic phase solution;

[0008] (3) The wetted porous base membrane is immersed in an aqueous solution, and then an organic solution is coated on the surface of the membrane to form a separation layer through interfacial polymerization of amine monomers and acyl chloride monomers. At the same time, sodium tetraphenylborate and organic potassium salt react simultaneously at the interface of the two phases to generate potassium tetraphenylborate nanoparticles, and the nanoparticles are dispersed in the entire polyamide separation layer to obtain a polyamide composite membrane with nanoparticles in the separation layer.

[0009] (4) The polyamide composite membrane containing nanoparticles in the separation layer is soaked in acetone to dissolve the potassium tetraphenylborate nanoparticles and form cavities, thus obtaining a polyamide composite membrane with a cavity structure.

[0010] (5) The polyamide composite membrane with cavity structure is heated in an oven to further crosslink, thereby obtaining a high-throughput polyamide composite membrane.

[0011] Preferably, the porous support layer is selected from one of polyethersulfone, polysulfone, polyimide, and polyvinylidene fluoride. Porous The support layer can be self-supporting or coated onto the surface of the nonwoven fabric;

[0012] Preferably, the amine monomer is one of piperazine, m-phenylenediamine, p-phenylenediamine, and m-phenyltriamine; the surfactant is one of sodium dodecyl sulfonate, sodium dodecyl sulfate, and hexadecyltrimethylammonium bromide; in the aqueous solution, the mass concentration of the amine monomer is 0.1%-3%; the mass concentration of the surfactant is 0.02%-0.1%; and the mass concentration of sodium tetraphenylborate is 0.01%-5%.

[0013] Preferably, the acyl chloride monomer is one of pyromellitic trimethylolpropionate chloride and its derivatives, pyromellitic tetramethylolpropionate chloride and its derivatives, isophthaloyl chloride and its derivatives, and terephthaloyl chloride and its derivatives; the organopotassium salt is a potassium carboxylate, potassium sulfonate, potassium alkoxide, or potassium phenolate compound; the organic solvent is one of n-hexane, cyclohexane, heptane, isoheptane, and trifluorotrichloroethane; in the organic phase solution, the mass concentration of the acyl chloride monomer is 0.1%-0.5%, and the mass concentration of the organopotassium salt is 0.01%-5%.

[0014] Preferably, the polyamide composite membrane containing nanoparticles in the separation layer is soaked in acetone for 30-240 minutes.

[0015] Preferably, the polyamide composite film with a cavity structure is heated in an oven at a temperature of 50℃-80℃ for 5-10 minutes.

[0016] Compared with existing technologies, the advantages of this invention are that the nanoparticles are formed in situ, and the size and total amount of nanoparticles can be controlled by the concentration and type of sodium tetraphenylborate and organic potassium salts; moreover, the nanoparticles uniformly span the entire polyamide separation layer, so the cavities formed after dissolution are also uniformly distributed throughout the polyamide separation layer. This effectively reduces the effective thickness of the polyamide separation layer without affecting the surface charge and cross-linking degree of the membrane, i.e., it does not affect the membrane's permeation selectivity. Attached Figure Description

[0017] Figure 1 A scanning electron microscope image of the polyamide composite film prepared without the addition of sodium tetraphenylborate and organic potassium salt as described in Comparative Example 1;

[0018] Figure 2 The image shows a scanning electron microscope image of the polyamide composite film that forms potassium tetraphenylborate nanoparticles as described in Example 1.

[0019] Figure 3 This is a scanning electron microscope image of the polyamide composite film that forms nanocavities as described in Example 1. Detailed Implementation

[0020] The following embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way.

[0021] This invention provides a method for preparing a high-throughput polyamide composite membrane: using sodium tetraphenylborate as an aqueous phase additive and organic potassium salt as an organic phase additive to form nanoparticles, which are then etched into a cavity structure, ultimately forming a polyamide composite membrane with a relatively thin effective separation layer.

[0022] The key concept of this invention lies in using nanoparticles generated through in-situ reaction of aqueous and organic phase additives at the interface as templates. These nanoparticles can be dispersed throughout the polyamide separation layer, and their particle size and content can be controlled by the content of sodium tetraphenylborate and organic potassium salts. The nanoparticles are ultimately dissolved in acetone, forming a separation layer with discontinuous cavities, which reduces the thickness of the polyamide separation layer, increases the permeation flux of the polyamide composite membrane, and retains its permeation selectivity.

[0023] The following examples 1-5 illustrate in detail a method for preparing high-throughput polyamide composite membranes provided by the present invention. Example 1

[0024] The method for preparing the polyamide composite nanofiltration membrane provided in this embodiment includes the following steps:

[0025] The polyethersulfone porous membrane was soaked in ethanol for 12 hours, then rinsed with water to remove the ethanol, maintaining a consistently moist state. The moistened membrane was then immersed in an aqueous solution containing 0.1% piperazine, 0.02% sodium dodecyl sulfate, and 0.1% sodium tetraphenylborate. After immersion for 2 minutes, the water droplets on the membrane surface were drained. An organic phase solution, consisting of a hexane solution containing 0.5% trimesoyl chloride and 0.01% potassium tert-butoxide, was coated onto the membrane surface. After coating for 2 minutes, excess organic phase solution was drained from the membrane surface. At this point, a polyamide separation layer had formed on the surface of the porous support layer, and potassium tetraphenylborate nanoparticles were simultaneously generated in situ on and inside the separation layer. The composite membrane was immersed in acetone for 60 minutes, then removed and dried at 50°C for 50 minutes to obtain a high-flux polyamide composite nanofiltration membrane. The pure water flux of the prepared high-flux polyamide composite nanofiltration membrane was 22 L·m⁻¹. -2 ·h -1 ·bar -1 .

[0026] Comparative Example 1: The steps are basically the same as in Example 1, except that sodium tetraphenylborate is not added to the aqueous phase and potassium tert-butoxide is not added to the organic phase. The pure water flux of the polyamide composite membrane prepared in Comparative Example 1 is 10 L·m -2 ·h -1 ·bar -1 .

[0027] The polyamide composite membranes prepared in Example 1 and Comparative Example 1 were subjected to selectivity tests with sodium sulfate (2 g / L) solution at 0.3 MPa and 25 °C. The sodium sulfate rejection rates of the polyamide composite nanofiltration membranes prepared in Example 1 and Comparative Example 1 were both above 99%. Example 2

[0028] A polysulfone porous membrane supported by a polyester nonwoven fabric was soaked in ethanol for 12 hours, then the ethanol on the surface of the porous membrane was washed with water, keeping it moist throughout. The moistened porous membrane was then immersed in an aqueous solution containing 1% m-phenylenediamine, 0.1% sodium dodecyl sulfate, and 0.5% sodium tetraphenylborate. After immersion for 1 minute, the water droplets on the membrane surface were drained. An organic phase solution was coated onto the membrane surface, which was a cyclohexane solution containing 0.1% pyromellitic tetracarboxylate chloride and 0.5% potassium stearate. After coating with the organic phase solution for 3 minutes, the excess organic phase solution on the membrane surface was drained. At this point, a polyamide separation layer had formed on the surface of the porous support layer, and potassium tetraphenylborate nanoparticles were simultaneously generated in situ inside the separation layer. The composite membrane was immersed in acetone for 30 min and then dried at 50°C for 10 min to obtain a high-flux polyamide composite reverse osmosis membrane. The pure water flux of the prepared high-flux polyamide reverse osmosis membrane was 8 L·m⁻¹. -2 ·h -1 ·bar -1 .

[0029] Comparative Example 2: The steps are basically the same as in Example 2, except that sodium tetraphenylborate is not added to the aqueous phase and potassium stearate is not added to the organic phase. The pure water flux of the polyamide composite membrane prepared in Comparative Example 2 is 3 L·m -2 ·h -1 ·bar -1 .

[0030] The reverse osmosis membranes prepared in Example 2 and Comparative Example 2 were subjected to selectivity tests with sodium chloride (2 g / L) solution at 0.6 MPa and 25 °C. The sodium chloride rejection rates of the reverse osmosis membranes prepared in Example 2 and Comparative Example 2 were both above 99%. Example 3

[0031] A porous polyvinylidene fluoride (PVDF) membrane was soaked in ethanol for 12 hours, then rinsed with water to remove the ethanol, maintaining a consistently moist state. The moistened membrane was then immersed in an aqueous solution containing 3% p-phenylenediamine, 0.02% hexadecyltrimethylammonium bromide, and 5% sodium tetraphenylborate. After 1 minute of immersion, the water droplets on the membrane surface were drained. An organic phase solution, consisting of an isoheptane solution containing 0.25% isophthaloyl chloride and 0.5% ethyl eosin, was coated onto the membrane surface. After 3 minutes of coating, excess organic phase solution was drained from the membrane surface. At this point, a polyamide separation layer had formed on the surface of the porous support layer, and potassium tetraphenylborate nanoparticles were generated in situ within the separation layer. The polyamide composite membrane was then immersed in acetone for 240 minutes and dried at 80°C for 5 minutes to obtain a high-flux polyamide composite membrane. The high-flux polyamide composite membrane prepared had a pure water flux of 15 L·m -2 ·h -1 ·bar -1 .

[0032] Comparative Example 3: The steps are basically the same as in Example 3, except that sodium tetraphenylborate is not added to the aqueous phase and ethyl eosin is not added to the organic phase. The pure water flux of the polyamide composite membrane prepared in Comparative Example 3 is 7 L·m -2 ·h -1 ·bar -1 .

[0033] The polyamide composite membranes prepared in Example 3 and Comparative Example 3 were subjected to selectivity tests with sodium sulfate (2 g / L) / sodium chloride (2 g / L) solutions at 0.6 MPa and 25 °C. The sodium sulfate rejection rate of the polyamide composite membranes prepared in Example 3 and Comparative Example 3 was above 99%, and the sodium chloride rejection rate was above 95%. Example 4

[0034] A porous polyimide membrane supported by a polyester nonwoven fabric was soaked in ethanol for 12 hours, then the ethanol on the surface of the porous membrane was washed with water, keeping it moist throughout. The moistened porous membrane was then immersed in an aqueous solution containing 1% m-phenylenediamine, 0.1% hexadecyltrimethylammonium bromide, and 2.5% sodium tetraphenylborate. After immersion for 1 minute, the water droplets on the membrane surface were drained. An organic phase solution was coated onto the membrane surface, which was a trifluorotrichloroethane solution containing 0.25% terephthaloyl chloride and 5% potassium perfluorooctyl sulfonate. After coating with the organic phase solution for 3 minutes, the excess organic phase solution on the membrane surface was drained. At this point, a polyamide separation layer had formed on the surface of the porous support layer, and potassium tetraphenylborate nanoparticles were simultaneously generated in situ inside the separation layer. The composite membrane was immersed in acetone for 120 min and then dried at 60°C for 5 min to obtain a high-flux polyamide composite reverse osmosis membrane. The pure water flux of the prepared high-flux reverse osmosis membrane was 7 L·m³. -2 ·h -1 ·bar -1 .

[0035] Comparative Example 4: The steps are basically the same as in Example 4, except that sodium tetraphenylborate is not added to the aqueous phase and potassium perfluorooctyl sulfonate is not added to the organic phase. The pure water flux of the polyamide composite membrane prepared in Comparative Example 4 is 3 L·m -2 ·h -1 ·bar -1 .

[0036] The reverse osmosis membranes prepared in Example 4 and Comparative Example 4 were subjected to selectivity tests with sodium chloride (2 g / L) solution at 0.6 MPa and 25 °C. The rejection rates of the reverse osmosis membranes prepared in both examples and comparative examples were above 99%. Example 5

[0037] A porous polyethersulfone membrane supported by a polyester nonwoven fabric was soaked in ethanol for 12 hours, then the ethanol on the surface of the porous membrane was washed with water, keeping it moist throughout. The moistened porous membrane was then immersed in an aqueous solution containing 3% piperazine, 0.05% sodium dodecyl sulfate, and 0.01% sodium tetraphenylborate. After immersion for 1 minute, the water droplets on the membrane surface were drained. An organic phase solution was coated onto the membrane surface, which was a heptane solution containing 0.25% trimesoyl chloride and 5% potassium stearate. After coating with the organic phase solution for 3 minutes, the excess organic phase solution on the membrane surface was drained. At this point, a polyamide separation layer had formed on the surface of the porous support layer, and potassium tetraphenylborate nanoparticles were simultaneously generated in situ inside the separation layer. The above-mentioned polyamide composite membrane was immersed in acetone for 30 min and then dried at 70°C for 8 min to obtain a high-flux polyamide composite nanofiltration membrane. The pure water flux of the prepared high-flux polyamide composite nanofiltration membrane was 23 L·m⁻¹. -2 ·h -1 ·bar -1 .

[0038] Comparative Example 5: The steps are basically the same as in Example 5, except that sodium tetraphenylborate is not added to the aqueous phase and potassium stearate is not added to the organic phase. The pure water flux of the nanofiltration membrane prepared in Comparative Example 5 is 11 L·m -2 ·h -1 ·bar -1 .

[0039] The polyamide composite membranes prepared in Example 5 and Comparative Example 5 were subjected to selectivity tests with sodium sulfate (2 g / L) solution at 0.3 MPa and 25 °C. The nanofiltration rejection rates of the nanofiltration membranes prepared in Example 5 and Comparative Example 5 were both above 99%.

[0040] As can be seen from the above embodiments, the high-flux polyamide composite membrane prepared by the present invention has a significantly improved permeation flux compared with the comparative example, but the permeation selectivity, i.e., the rejection rate, has not changed significantly.

[0041] In summary, the present invention provides a method for preparing high-flux polyamide composite membranes, which can reduce the effective thickness of the polyamide separation layer and provide a method for preparing polyamide composite membranes with high permeation flux and high permeation selectivity. The polyamide composite membranes provided by the present invention can be widely used in environmental, food, pharmaceutical, and chemical fields.

[0042] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made based on the content of the present invention specification and drawings, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

[0043] Note: 1. In all embodiments, the base film is first immersed in the aqueous solution and then coated with the organic solution. However, the patent describes coating the aqueous solution and the organic solution in sequence. It is recommended to make a uniform modification (marked in red in the patent).

[0044] 2. As described in the embodiments, the support layer is a polyethersulfone porous base membrane, a polysulfone porous base membrane, a polyvinylidene fluoride porous base membrane, a polyimide porous base membrane, or a polyethersulfone porous base membrane; while the porous support layer described in the patent application is selected from one of polyethersulfone, polysulfone, polyimide, or polyvinylidene fluoride.

Claims

1. A method of preparing a high flux polyamide composite membrane, characterized in that, It comprises the following steps: (1) dissolving amine monomer, surfactant and sodium tetraphenylborate in water to obtain an aqueous solution; (2) dissolving acyl chloride monomer and organic potassium salt in an organic solvent to obtain an organic phase solution; (3) immersing the wet porous base film in the aqueous solution, and then coating the organic phase solution on the surface of the film to make the amine monomer and the acyl chloride monomer form a separation layer through interfacial polymerization; at the same time, the sodium tetraphenylborate and the organic potassium salt are synchronously reacted at the interface of the two phases to generate potassium tetraphenylborate nanoparticles, and the nanoparticles are dispersed in the entire polyamide separation layer to obtain a polyamide composite membrane containing nanoparticles in the separation layer; (4) soaking the polyamide composite membrane containing nanoparticles in the separation layer in acetone to dissolve the potassium tetraphenylborate nanoparticles to form cavities, thereby obtaining a polyamide composite membrane with a cavity structure; (5) heating the polyamide composite membrane with a cavity structure in an oven for further crosslinking to obtain a high-flux polyamide composite membrane.

2. The method of claim 1, wherein the high flux polyamide composite membrane is prepared by the steps of: The porous base film is selected from one of polyether sulfone porous base film, polysulfone porous base film, polyimide porous base film, and polyvinylidene fluoride porous base film, and the porous base film is self-supporting or coated on the surface of a non-woven fabric.

3. The method of claim 1, wherein the high flux polyamide composite membrane is prepared by the steps of: The amine monomer is one of piperazine, m-phenylenediamine, p-phenylenediamine and m-phenyl triamine; the surfactant is one of sodium dodecyl sulfonate, sodium dodecyl sulfate and cetyltrimethylammonium bromide; in the aqueous solution, the mass concentration of the amine monomer is 0.1%-3%, the mass concentration of the surfactant is 0.02%-0.1%, and the mass concentration of sodium tetraphenylborate is 0.01%-5%.

4. The method of claim 1, wherein the high flux polyamide composite membrane is prepared by the steps of: The acyl chloride monomer is one of trimesoyl chloride and its derivatives, pyromellitic dichloride and its derivatives, isophthaloyl chloride and its derivatives, and terephthaloyl chloride and its derivatives; the organic potassium salt is a potassium carboxylate, a potassium sulfonate, a potassium alcoholate or a potassium phenolate; the organic solvent is selected from one of n-hexane, cyclohexane, heptane, isomeric heptane and trifluorotrichloroethane; in the organic phase solution, the mass concentration of the acyl chloride monomer is 0.1%-0.5%, and the mass concentration of the organic potassium salt is 0.01%-5%.

5. The method for preparing a high-throughput polyamide composite membrane according to claim 1, characterized in that, The polyamide composite membrane containing nanoparticles in the separation layer is soaked in acetone for 30-240 min.

6. The method of claim 1, wherein the high flux polyamide composite membrane is prepared by the steps of: The polyamide composite membrane with a cavity structure is heated in an oven at a temperature of 50-80℃ for 5-10 min.

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