An organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles and a method for preparing the same

Abstract

The application provides an organic-solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles and a preparation method thereof, and belongs to the technical field of nanofiltration membranes. The organic-solvent-resistant nanofiltration membrane provided by the application comprises a support layer and a polyamide separation layer located on the surface of the support layer; the support layer is a polyimide ultrafiltration membrane base film; the polyamide separation layer is a modified polyamide layer; the modification method is modification by adding an intermediate layer and an additive; the intermediate layer is polydopamine / polyethyleneimine; and the additive is aminozed attapulgite nanoparticles. The polydopamine / polyethyleneimine and aminozed attapulgite are used in synergistic action to prepare the organic-solvent-resistant nanofiltration membrane, so that the organic-solvent-resistant nanofiltration membrane has high permeation flux and high retention rate.

Description

A nanofiltration membrane resistant to organic solvents containing an active intermediate layer and active nanoparticles and its preparation method. Technical Field

[0001] This invention relates to the field of nanofiltration membrane technology, and in particular to an organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles, and a method for preparing the same. Background Technology

[0002] Industries such as paint manufacturing, food processing, pharmaceuticals, chemicals, and paper printing use large quantities of organic solvents. Direct discharge of these solvents poses a serious environmental threat and causes resource depletion. Traditional methods for recovering organic solvents include extraction, distillation, and column chromatography, but these methods are energy-intensive and produce high emissions. Membrane separation technology, developed in recent decades, offers advantages such as high selectivity, low energy consumption, and mild operating conditions. Currently, membrane separation technology is widely used in wastewater treatment, material separation, and seawater desalination. Organic solvent-resistant nanofiltration membranes are also being applied in the field of organic solvent separation and recovery.

[0003] Membrane separation technologies can be classified into microfiltration, ultrafiltration, nanofiltration, and reverse osmosis based on the pore size of the membrane. Among them, nanofiltration technology has a good retention capacity for divalent ions and organic molecules with a molecular weight of 200 Da or higher. The main process for preparing organic solvent-resistant nanofiltration membranes is interfacial polymerization, which uses polyamines (m-phenylenediamine or piperazine) and polyacrylamide chlorides (trimethylammonium pyromellitic chloride) to prepare a polyamide separation layer. The unreacted acrylamide chloride groups undergo hydrolysis to generate carboxylic acids, which in turn give the membrane surface a greater negative charge, thus providing a better repulsion effect on some anionic substances.

[0004] Similar to other membrane separation technologies, nanofiltration technology inevitably faces the trade-off between permeability and rejection rate during operation. Patent CN 111992039 B constructs a ZIF-8 interlayer, preparing it on a porous base membrane. The resulting polyamide separation layer, prepared by interfacial polymerization, is thin and defect-free, but the interlayer preparation process is time-consuming. Patent CN 114534514 A discloses an ultrathin composite solvent-resistant membrane using an in-situ complexed network of tannic acid and copper ions as the interlayer, but its solvent flux remains low. Patent CN 102151490A uses polyamide to embed inorganic nanoparticles to prepare a composite membrane, improving separation efficiency; however, the aggregation of inorganic nanoparticles leads to uneven distribution, resulting in unstable membrane performance. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an organic solvent resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles and a method for preparing the same. The organic solvent resistant nanofiltration membrane provided by the present invention has high permeation flux and rejection rate.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] The present invention provides an organic solvent resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles, comprising a support layer and a polyamide separation layer located on the surface of the support layer;

[0008] The support layer is a polyimide ultrafiltration membrane base membrane;

[0009] The polyamide separation layer is a modified polyamide layer; the modification method is to modify it by adding an intermediate layer and an additive; the intermediate layer is polydopamine / polyethyleneimine; the additive is aminated attapulgite nanoparticles.

[0010] This invention also provides a method for preparing the organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles as described in the above technical solution, comprising the following steps:

[0011] (1) The polyimide casting solution is uniformly spread on the carrier and phase inversion is carried out in a water bath to obtain a polyimide ultrafiltration membrane;

[0012] (2) The polyimide ultrafiltration membrane obtained in step (1) is subjected to a crosslinking reaction with a crosslinking agent solution to obtain a crosslinked polyimide ultrafiltration membrane;

[0013] (3) The bright side of the cross-linked polyimide ultrafiltration membrane obtained in step (2) is immersed in a polydopamine / polyethyleneimide tris(hydroxymethyl)aminomethane-hydrochloric acid solution for coating, to obtain a polydopamine / polyethyleneimide coated cross-linked polyimide ultrafiltration membrane.

[0014] (4) Immerse the bright side of the polydopamine / polyethyleneimine coated cross-linked polyimide ultrafiltration membrane obtained in step (3) in an aqueous solution containing aminated attapulgite nanoparticles to obtain a polydopamine / polyethyleneimine coated cross-linked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles.

[0015] (5) The polydopamine / polyethyleneimine-coated cross-linked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles obtained in step (4) is immersed in an organic phase solution containing polyacrylamide chloride to carry out an interfacial polymerization reaction to form a polyamide separation layer and obtain a solvent-resistant nanofiltration membrane precursor.

[0016] (6) The solvent-resistant nanofiltration membrane precursor obtained in step (5) is activated by solvent to obtain the organic solvent-resistant nanofiltration membrane.

[0017] Preferably, the polyimide casting solution in step (1) is composed of polyimide polymer P84, a pore-forming agent, and a highly polar solvent.

[0018] More preferably, the pore-forming agent is at least one of polyethylene glycol, polyvinylpyrrolidone, or hydroxypropyl cellulose; and the strongly polar solvent is at least one of N,N-dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.

[0019] Preferably, the crosslinking agent solution in step (2) is a crosslinking solution of hexamethylenediamine / isopropanol; the concentration of the crosslinking agent solution is 120 g / L; and the crosslinking reaction time is 12-18 h.

[0020] Preferably, the mass ratio of polydopamine to polyethyleneimine in step (3) is (1:1) to (1:3); the molecular weight of the polyethyleneimine is 600 Da to 10000 Da.

[0021] Preferably, the coating time in step (3) is 15-60 min.

[0022] Preferably, in step (4), the mass fraction of the aminated attapulgite nanoparticles in the aqueous solution containing the aminated attapulgite nanoparticles is 0.05wt%-0.20wt%; and the soaking time is 120-180s.

[0023] Preferably, the interfacial polymerization reaction time in step (5) is 30-90 s.

[0024] Preferably, the solvent used for solvent activation in step (6) is at least one of N,N-dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.

[0025] Beneficial technical effects:

[0026] 1. The present invention uses polydopamine / polyethyleneimine as an intermediate layer, which can increase the hydrophilicity of the membrane, thereby reducing the diffusion rate of aqueous monomers to the organic phase, making the polyamide membrane thinner, reducing the solvent transport resistance, and increasing the flux.

[0027] 2. The present invention uses aminated attapulgite nanoparticles as an additive, which can covalently bond with the acyl chloride groups in the organic phase monomer, and can be better embedded in the polyamide separation layer.

[0028] 3. The nanofiltration membrane prepared by this invention has both high flux and high rejection rate, and has good application prospects. Attached Figure Description

[0029] Figure 1 shows the XPS spectra of attapulgite and aminated attapulgite nanoparticles prepared in Example 1.

[0030] Figure 2 shows the scanning electron microscope (SEM) images and atomic force microscope (AFM) test images of the base films at different coating times for PDA / PEI in Comparative Examples 1-4.

[0031] Figure 3 shows macroscopic views of the base films under different coating times for PDA / PEI in Comparative Examples 1-4;

[0032] Figure 4 shows the methanol flux and Evans blue dye rejection rate of the organic solvent-resistant nanofiltration membranes prepared in Comparative Examples 1-4.

[0033] Figure 5 shows the methanol flux and Evans blue dye rejection rate of the organic solvent-resistant nanofiltration membranes prepared in Examples 1-4. Detailed Implementation

[0034] The present invention provides an organic solvent resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles, comprising a support layer and a polyamide separation layer located on the surface of the support layer;

[0035] The support layer is a polyimide ultrafiltration membrane base membrane;

[0036] The polyamide separation layer is a modified polyamide layer; the modification method is to modify it by adding an intermediate layer and an additive; the intermediate layer is polydopamine / polyethyleneimine; the additive is aminated attapulgite nanoparticles.

[0037] In this invention, polydopamine / polyethyleneimine is used as an intermediate layer, which can increase the hydrophilicity of the membrane, thereby reducing the diffusion rate of aqueous monomers to the organic phase, making the polyamide membrane thinner, reducing the solvent transport resistance, and increasing the flux. In this invention, aminated attapulgite nanoparticles are used as additives, which can covalently bond with the acyl chloride groups in the organic phase monomers and can be better embedded in the polyamide separation layer.

[0038] In this invention, the preparation method of the aminated attapulgite nanoparticles is as follows: attapulgite is acidified, filtered, dried, and then sonicated in a solvent. Then, an aminated silane coupling agent is added and reacted at 50°C for 2 hours. After the reaction is completed, the excess solvent is removed by centrifugation and the mixture is washed with anhydrous ethanol to remove the excess aminated silane coupling agent.

[0039] In this invention, the acidification solvent is hydrochloric acid, and the concentration of hydrochloric acid is 1-5 mol / L; the solid-liquid ratio of attapulgite clay to hydrochloric acid is 1:(4-6); the acidification time is 4-6 h; the acidification method is mixing and stirring; in this invention, the solvent is water or toluene, preferably toluene; the aminosilane coupling agent is (3-aminopropyl)trimethoxysilane (APS) or (3-aminopropyl)triethoxysilane (APTES), preferably (3-aminopropyl)trimethoxysilane (APS).

[0040] This invention also provides a method for preparing the organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles as described in the above technical solution, comprising the following steps:

[0041] (1) The polyimide casting solution is uniformly spread on the carrier and phase inversion is carried out in a water bath to obtain a polyimide ultrafiltration membrane;

[0042] (2) The polyimide ultrafiltration membrane obtained in step (1) is subjected to a crosslinking reaction with a crosslinking agent solution to obtain a crosslinked polyimide ultrafiltration membrane;

[0043] (3) The bright side of the cross-linked polyimide ultrafiltration membrane obtained in step (2) is immersed in a polydopamine / polyethyleneimide tris(hydroxymethyl)aminomethane-hydrochloric acid solution for coating, to obtain a polydopamine / polyethyleneimide coated cross-linked polyimide ultrafiltration membrane.

[0044] (4) Immerse the bright side of the polydopamine / polyethyleneimine coated cross-linked polyimide ultrafiltration membrane obtained in step (3) in an aqueous solution containing aminated attapulgite nanoparticles to obtain a polydopamine / polyethyleneimine coated cross-linked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles.

[0045] (5) The polydopamine / polyethyleneimine-coated cross-linked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles obtained in step (4) is immersed in an organic phase solution containing polyacrylamide chloride to carry out an interfacial polymerization reaction to form a polyamide separation layer and obtain a solvent-resistant nanofiltration membrane precursor.

[0046] (6) The solvent-resistant nanofiltration membrane precursor obtained in step (5) is activated by solvent to obtain the organic solvent-resistant nanofiltration membrane.

[0047] In this invention, unless otherwise specified, all raw material components are commercially available products well known to those skilled in the art.

[0048] In this invention, a polyimide casting solution is uniformly spread on a carrier and subjected to phase transformation in a water bath to obtain a polyimide ultrafiltration membrane.

[0049] In this invention, the concentration of the polyimide casting solution is preferably 20 wt%; the polyimide casting solution is composed of polyimide polymer P84, a pore-forming agent, and a highly polar solvent; the pore-forming agent is preferably at least one of polyethylene glycol, polyvinylpyrrolidone, or hydroxypropyl cellulose, more preferably polyvinylpyrrolidone; the highly polar solvent is preferably at least one of N,N-dimethylformamide (DMF), dimethylacetamide (DMAc), or N-methylpyrrolidone (NMP), more preferably N,N-dimethylformamide (DMF).

[0050] In this invention, the carrier is preferably a non-woven fabric material; the non-woven fabric material is preferably polyethylene terephthalate, polypropylene, nylon, viscose fiber, acrylic fiber, ethylene fiber or chlorofiber; more preferably polyethylene terephthalate.

[0051] In this invention, the phase transformation is first carried out in a deionized water coagulation bath for 10-30 minutes, and then the membrane is transferred to new deionized water to continue the phase transformation for 1-3 days to obtain a polyimide ultrafiltration membrane.

[0052] After the phase transformation is completed, the present invention further includes washing the phase transformation membrane with an organic solvent; the organic solvent is preferably an isopropanol solution; the washing is performed 4-6 times, each time for 40-60 minutes, to remove residual strongly polar proton solvents and water in the membrane.

[0053] After obtaining the polyimide ultrafiltration membrane, the present invention performs a crosslinking reaction between the obtained polyimide ultrafiltration membrane and a crosslinking agent solution to obtain a crosslinked polyimide ultrafiltration membrane.

[0054] In this invention, the crosslinking agent solution is preferably a hexamethylenediamine / isopropanol crosslinking solution; the concentration of the hexamethylenediamine / isopropanol crosslinking solution is preferably 110-130 g / L, more preferably 120 g / L. This invention improves the solvent resistance of the prepared organic solvent-resistant nanofiltration membrane through a crosslinking reaction.

[0055] In this invention, after the crosslinking reaction is completed, the crosslinked membrane is further cleaned using an organic solvent; the organic solvent is preferably isopropanol; the number of cleaning cycles is preferably 4-6 times, more preferably 4 times, and the cleaning time for each cycle is preferably 40-60 minutes, preferably 60 minutes. In this invention, isopropanol is continued after the crosslinking process to remove residual hexamethylenediamine from the membrane.

[0056] After obtaining the cross-linked polyimide ultrafiltration membrane, the present invention immerses the bright side of the obtained cross-linked polyimide ultrafiltration membrane in a tris(hydroxymethyl)aminomethane-hydrochloric acid (Tris-HCl) solution of polydopamine (PDA) / polyethyleneimine (PEI) for coating, thereby obtaining a polydopamine (PDA) / polyethyleneimine (PEI) coated cross-linked polyimide ultrafiltration membrane.

[0057] In this invention, the mass ratio of polydopamine to polyethyleneimine is preferably (1:1) to (1:3), more preferably 1:1; the molecular weight of polyethyleneimine is preferably 600-10000 Da, more preferably 600 Da, 1800 Da, or 10000 Da, and most preferably 600 Da. Increasing the molecular weight of polyethyleneimine significantly inhibits the deposition of PDA / PEI, which is detrimental to the co-deposition process, so the molecular weight of polyethyleneimine is controlled at 600 Da. In this invention, the pH value of the tris(hydroxymethyl)aminomethane-hydrochloric acid (Tris-HCl) solution is preferably 8-9, more preferably 8.5; the Tris concentration in the Tris-HCl solution is preferably 40-60 mmol / L, more preferably 50 mmol / L. In this invention, the application time is preferably 15-60 min, more preferably 45 min.

[0058] In this invention, the bright side of the obtained cross-linked polyimide ultrafiltration membrane is immersed in a tris(hydroxymethyl)aminomethane-hydrochloric acid (Tris-HCl) solution of polydopamine (PDA) / polyethyleneimine (PEI) for coating. Dopamine can self-polymerize in a weakly alkaline environment, and the introduction of polyethyleneimine can disrupt the non-covalent interactions in the polydopamine aggregates, which can effectively inhibit the formation of particles.

[0059] After obtaining the PDA / PEI-coated cross-linked polyimide ultrafiltration membrane, the present invention immerses one side of the obtained PDA / PEI-coated cross-linked polyimide ultrafiltration membrane in an aqueous solution containing aminated attapulgite nanoparticles to obtain a PDA / PEI-coated cross-linked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles.

[0060] In this invention, the aqueous solution containing aminated attapulgite nanoparticles is composed of an amino-based aqueous monomer, aminated attapulgite, and pure water. The amino-based aqueous monomer is m-phenylenediamine or piperazine. The concentration of the amino-based aqueous monomer in the aqueous solution containing aminated attapulgite nanoparticles is 2.0-3.0 wt%, and the mass fraction of the aminated attapulgite nanoparticles is preferably 0.5 wt%-0.2 wt%, more preferably 0.15 wt%. The aminated attapulgite selected in this invention can compete with the amino-based aqueous monomer for reaction with polyacrylamide chlorides, thus enabling better embedding into the polyamide layer.

[0061] In this invention, the soaking time is preferably 120-180 seconds. After soaking, the excess aqueous solution is removed using a roller.

[0062] After obtaining a PDA / PEI-coated cross-linked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles, the present invention immerses the PDA / PEI-coated cross-linked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles in an organic phase solution containing polyacrylamide chlorides to carry out an interfacial polymerization reaction, forming a polyamide separation layer, and obtaining a solvent-resistant nanofiltration membrane precursor.

[0063] In this invention, the polyacrylamide chloride is preferably trimesoyl chloride; the organic phase solution is preferably n-hexane; and the interfacial polymerization reaction time is preferably 30-90 s.

[0064] After obtaining the solvent-resistant nanofiltration membrane precursor, the present invention activates the solvent-resistant nanofiltration membrane precursor with a solvent to obtain the organic solvent-resistant nanofiltration membrane.

[0065] In this invention, the solvent used for solvent activation is preferably at least one of N,N-dimethylformamide (DMF), dimethylacetamide (DMAc), or N-methylpyrrolidone (NMP), more preferably N,N-dimethylformamide (DMF); the solvent activation temperature is preferably 60-90°C. The purpose of solvent activation of the precursor for preparing the solvent-resistant nanofiltration membrane in this invention is to remove small-molecule polyamide chains, thereby increasing the permeation flux of the prepared solvent-resistant nanofiltration membrane.

[0066] The present invention also provides the application and use of the solvent-resistant nanofiltration membrane in the field of dye separation.

[0067] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0068] In the following embodiments, the solvent-resistant nanofiltration membrane of the present invention operates at a pressure of 10 bar, where permeation flux and rejection rate are two important parameters.

[0069] Calculate the permeation flux using formula (I) and the rejection rate using formula (II). Formulas (I) and (II) are as follows:

[0070] Formula (1)

[0071] Formula (II)

[0072] In Formula (I), A is the effective membrane area (m²). 2 ), t operation time (h) V represents the volume (L) of the permeate during the operating time. P is the operating pressure (bar);

[0073] In Formula 2, C fC represents the concentration of the dye in the raw material solution. p The concentration of the dye in the permeate is denoted as R. The rejection rate R is between 0 and 100%. The larger the R value, the less dye permeates and the better the separation performance.

[0074] In this invention, the dye separation performance of the prepared solvent-resistant nanofiltration membrane was tested. The dye was Evans blue, the dye solvent was methanol, and the dye concentration was 20 mg / L.

[0075] Example 1

[0076] Preparation of amination-modified attapulgite nanoparticles:

[0077] 10g of attapulgite was acidified with 3mol / L hydrochloric acid at room temperature for 5h, filtered, and the acidified attapulgite was dried under vacuum at 100℃ for 12h. Then, 3g of acidified attapulgite was sonicated in 50mL of toluene for 30min, and 3mL of APS was added and reacted at 50℃ for 2h. After the reaction, the excess toluene solvent was removed by centrifugation at 8000r / min, and the mixture was washed 2-3 times with anhydrous ethanol to remove excess APS.

[0078] Figure 1 shows the XPS spectra of attapulgite and aminated attapulgite. A binding energy peak for N element can be observed at 400 eV, proving the successful synthesis of aminated attapulgite.

[0079] The method for preparing the organic solvent-resistant nanofiltration membrane is as follows:

[0080] (1) Weigh 3.0g of polyimide polymer (P84) and 0.15g of polyvinylpyrrolidone (PVP) and dissolve them in 11.85g of DMF to prepare a casting solution with a mass fraction of 20wt%. Stir at room temperature for 24h, let stand for 2 days to remove excess air bubbles, spread the casting solution evenly on polyethylene terephthalate nonwoven fabric, coat it with a 200μm doctor blade, quickly transfer it to a deionized water coagulation bath for phase inversion for 10min, continue to transfer it to a new deionized water coagulation bath for phase inversion for 2 days, and soak the polyimide ultrafiltration membrane after phase inversion in isopropanol solution for washing 4 times, 60min each time to obtain the polyimide ultrafiltration membrane;

[0081] (2) The polyimide ultrafiltration membrane was placed in a 120 g / L hexamethylenediamine / isopropanol solution for crosslinking for 16 h. After the crosslinking was completed, it was placed in an isopropanol solution for washing 4 times, each time for 60 min, to obtain the crosslinked polyimide ultrafiltration membrane.

[0082] (3) Prepare a 100ml Tris-HCl buffer solution with a concentration of 50mmol / L and pH=8.5, and weigh out 0.2g of dopamine hydrochloride (DA) and 0.2g of polyethyleneimine (PEI) with a molecular weight of 600Da and dissolve them in the above buffer solution. Immerse one side of the cross-linked polyimide ultrafiltration membrane in the DA / PEI Tris-HCl buffer solution and coat it evenly for 45min using a shaker to obtain a PDA / PEI coated cross-linked polyimide ultrafiltration membrane.

[0083] (4) The PDA / PEI coated cross-linked polyimide ultrafiltration membrane was immersed on one side in an aqueous solution containing 2.0 wt% m-phenylenediamine and 0.05 wt% aminated attapulgite nanoparticles for 120 s, and the excess aqueous solution was removed by rolling with a roller.

[0084] (5) The precursor of the organic solvent resistant nanofiltration membrane was immersed again in a 0.01 wt% pyromellitic acid chloride organic phase solution for interfacial polymerization for 60 s to obtain the precursor of the organic solvent resistant nanofiltration membrane.

[0085] (4) The precursor of the organic solvent resistant nanofiltration membrane was activated in DMF at 80°C for 30 min to remove small molecule polyamide chains and obtain the organic solvent resistant nanofiltration membrane.

[0086] The prepared organic solvent-resistant nanofiltration membrane was stored in a methanol solution for subsequent reaction testing. The membrane was named TFC-45-0.05.

[0087] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.58% rejection rate for Evans blue and a methanol permeation flux of 10.58 L / (m³). 2 ·h·bar).

[0088] Example 2

[0089] Same as Example 1, except that the content of aminated attapulgite nanoparticles in step (4) is adjusted to 0.10 wt%. The membrane is named TFC-45-0.10.

[0090] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.45% rejection rate for Evans blue and a methanol permeation flux of 11.35 L / (m³). 2 ·h·bar).

[0091] Example 3

[0092] Same as Example 1, except that the content of aminated attapulgite nanoparticles in step (4) is adjusted to 0.15 wt%. The membrane is named TFC-45-0.15.

[0093] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.4% rejection rate for Evans blue and a methanol permeation flux of 13.59 L / (m³). 2 ·h·bar).

[0094] Example 4

[0095] Same as Example 1, except that the content of aminated attapulgite nanoparticles in step (4) is adjusted to 0.20 wt%. The membrane is named TFC-45-0.20.

[0096] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.50% rejection rate for Evans blue and a methanol permeation flux of 12.15 L / (m³). 2 ·h·bar).

[0097] Comparative Example 1

[0098] Same as Example 1, except that the coating time in step (3) is adjusted to 15 min, and no nanoparticles are added. This film is named TFN-15.

[0099] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.28% rejection rate for Evans blue and a methanol permeation flux of 7.43 L / (m³). 2 ·h·bar).

[0100] Comparative Example 2

[0101] Same as Example 1, except that the coating time in step (3) is adjusted to 30 min, and no nanoparticles are added. This film is named TFN-30.

[0102] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.22% rejection rate for Evans blue and a methanol permeation flux of 10.23 L / (m³). 2 ·h·bar).

[0103] Comparative Example 3

[0104] Same as Example 1, except that step (4) does not involve the addition of any amount of nanoparticles. This membrane is named TFN-45.

[0105] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.38% rejection rate for Evans blue and a methanol permeation flux of 10.38 L / (m³). 2 ·h·bar).

[0106] Comparative Example 4

[0107] Same as Example 1, except that the coating time in step (3) was adjusted to 60 min, and no nanoparticles were added. This film was named TFN-60.

[0108] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.52% rejection rate for Evans blue and a methanol permeation flux of 8.38 L / (m³). 2 ·h·bar).

[0109] Comparative Example 5

[0110] Same as Example 3, except that the aminated attapulgite nanoparticles in step (4) are replaced with acidified attapulgite nanoparticles. This film is named TFN-45-0.15A.

[0111] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.59% rejection rate for Evans blue and a methanol permeation flux of 11.89 L / (m³). 2 ·h·bar).

[0112] Comparative Example 6

[0113] Same as Example 1, except that aminated attapulgite nanoparticles are not added in step (4), and the coating time is 0 min. This film is named TFC.

[0114] The nanofiltration performance of the membrane was tested using a 20 mg / L Evans blue-methanol solution. The membrane showed a 99.21% rejection rate for Evans blue and a methanol permeation flux of 7.12 L / (m³). 2 ·h·bar).

[0115] Figure 2 shows the scanning electron microscope (SEM) and atomic force microscope (AFM) images of the base films at different coating times in Comparative Examples 1-4. It can be seen that although the introduction of PEI can improve the formation of aggregated particles on the film surface and make the aggregates more dispersed, a small number of nodules still exist on the film surface. This is unavoidable during the film modification process. SEM analysis shows that with increasing deposition time, the nodules on the film surface gradually increase in size and number. AFM testing further confirms that the surface roughness of the film increases.

[0116] Figure 3 shows the macroscopic surface of the base film under different coating times in Comparative Examples 1-4. It can be seen that the film color becomes darker as the coating time increases, which further proves the successful coating of PDA / PEI.

[0117] Figure 4 shows the methanol flux and Evans blue dye rejection rate of the organic solvent-resistant nanofiltration membranes under different coating times in Comparative Examples 1-4. It can be seen that the methanol flux gradually increases with time, while the Evans blue dye rejection rate remains above 99%. This is because the coated PDA / PEI intermediate layer has good hydrophilicity and can adsorb a certain amount of m-phenylenediamine molecules to slow down the diffusion rate to the organic phase, thus making the generated polyamide separation layer thinner and increasing the flux. However, further extending the coating time shows a decreasing trend in methanol flux, which may be because the PDA self-polymerization time is too long, leading to excessive oxidation, which reduces the number of crosslinking sites of surface active groups and ultimately reduces the subsequent reaction activity.

[0118] Figure 5 shows the methanol flux and Evans blue dye rejection rate of organic solvent-resistant nanofiltration membranes with different particle addition amounts. The highest methanol flux reached 13.59 L / (m²). 2 The Evans blue dye rejection rate remained above 99% when the particle concentration was increased further. The decrease in flux may be due to the excessive particle concentration clogging the membrane pores, which in turn reduced the flux.

[0119] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An organic solvent-resistant nanofiltration membrane comprising an active intermediate layer and active nanoparticles, characterized in that, The membrane includes a support layer and a polyamide separation layer located on the surface of the support layer; the support layer is a polyimide ultrafiltration membrane base membrane; the polyamide separation layer is a modified polyamide layer; the modification method is by adding an intermediate layer and an additive; the intermediate layer is polydopamine / polyethyleneimine; the additive is aminated attapulgite nanoparticles. The method for preparing the organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles includes the following steps: (1) uniformly coating a polyimide casting solution onto a carrier and performing a phase inversion in a water bath to obtain a polyimide ultrafiltration membrane; (2) subjecting the polyimide ultrafiltration membrane obtained in step (1) to a crosslinking reaction with a crosslinking agent solution to obtain a crosslinked polyimide ultrafiltration membrane; (3) immersing the bright side of the crosslinked polyimide ultrafiltration membrane obtained in step (2) in a polydopamine / polyethyleneimine tris(hydroxymethyl)aminomethane-hydrochloric acid solution for coating to obtain a polydopamine / polyethyleneimine coated crosslinked polyimide ultrafiltration membrane; (4) immersing the bright side of the polydopamine / polyethyleneimine coated crosslinked polyimide ultrafiltration membrane obtained in step (3) in an aqueous solution containing aminated attapulgite nanoparticles to obtain a polydopamine / polyethyleneimine coated crosslinked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles. (5) The polydopamine / polyethyleneimine-coated cross-linked polyimide ultrafiltration membrane containing aminated attapulgite nanoparticles obtained in step (4) is immersed in an organic phase solution containing polyacrylamide chloride for interfacial polymerization reaction to form a polyamide separation layer and obtain a solvent-resistant nanofiltration membrane precursor; (6) The solvent-resistant nanofiltration membrane precursor obtained in step (5) is solvent-activated to obtain the organic solvent-resistant nanofiltration membrane; the molecular weight of the polyethyleneimine is 600 Da; the preparation method of the aminated attapulgite nanoparticles is as follows: the attapulgite is acidified, filtered, dried, and then sonicated in a solvent, and then an aminated silane coupling agent is added and reacted at 50°C for 2 h. After the reaction, the excess solvent is removed by centrifugation and washed with anhydrous ethanol to remove the excess aminated silane coupling agent; the aminated silane coupling agent is (3-aminopropyl)trimethoxysilane or (3-aminopropyl)triethoxysilane.

2. The organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles according to claim 1, characterized in that, The polyimide casting solution in step (1) is composed of polyimide polymer P84, a pore-forming agent, and a highly polar solvent.

3. The organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles according to claim 2, characterized in that, The pore-forming agent is at least one of polyethylene glycol, polyvinylpyrrolidone, or hydroxypropyl cellulose; the highly polar solvent is at least one of N,N-dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.

4. The organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles according to claim 1, characterized in that, The crosslinking agent solution in step (2) is a crosslinking solution of hexamethylenediamine / isopropanol; the concentration of the crosslinking agent solution is 110-130 g / L; and the crosslinking reaction time is 12-18 h.

5. The organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles according to claim 1, characterized in that, The mass ratio of polydopamine to polyethyleneimine in step (3) is (1:1)-(1:3).

6. The organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles according to claim 1, characterized in that, The coating time in step (3) is 15-60 min.

7. The organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles according to claim 1, characterized in that, In step (4), the mass fraction of the aminated attapulgite nanoparticles in the aqueous solution containing the aminated attapulgite nanoparticles is 0.05wt%-0.20wt%; the soaking time is 120-180s.

8. The organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles according to claim 1, characterized in that, The interfacial polymerization reaction time in step (5) is 30-90 s.

9. The organic solvent-resistant nanofiltration membrane containing an active intermediate layer and active nanoparticles according to claim 1, characterized in that, The solvent used for solvent activation in step (6) is at least one of N,N-dimethylformamide, dimethylacetamide, or N-methylpyrrolidone.

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