Composite nanofiltration membrane, method for preparing the same and use thereof

Abstract

The application relates to the field of membrane separation technology and discloses a composite nanofiltration membrane and a preparation method and application thereof. The composite nanofiltration membrane comprises a reinforcing layer and a support layer, an intermediate layer and a separation layer which are sequentially attached to the surface of the reinforcing layer; the support layer is a polymer layer containing nanometer manganese dioxide; the intermediate layer is a tannic acid-iron ion complex layer; and the separation layer is a polyamide layer. The support layer of the composite nanofiltration membrane is a polymer layer containing nanometer manganese dioxide, the nanometer manganese dioxide is uniformly dispersed in the polymer layer, interacts with tannic acid in the intermediate layer, can provide a channel for solvent transmission with the gap between the polymer matrix, reduces the resistance of solvent passing, and improves the flux. Meanwhile, the intermediate layer and the separation layer interact, so that the thickness of the separation layer is relatively thin, and the flux of the composite nanofiltration membrane is further improved.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to a composite nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Organic solvent nanofiltration is a green and energy-saving novel membrane technology for treating organic solvents, with broad application prospects in industries such as petrochemicals, food, and pharmaceuticals. Most existing commercial organic solvent nanofiltration membranes are monolithic asymmetric membranes prepared by phase inversion. Due to their thicker skin and higher filtration resistance, they have lower flux and require higher operating pressures. Thin-layer composite membranes prepared by interfacial polymerization consist of a thin selective separation layer and a porous support substrate. Because both layers can be individually controlled to achieve better overall performance, this has become a research hotspot for many scholars both domestically and internationally.

[0003] CN104128102A discloses a cyclodextrin-modified composite organic solvent nanofiltration membrane and its preparation method. The method uses a hydrolyzed polyacrylonitrile ultrafiltration membrane as the base membrane. An aqueous solution is prepared using amine compounds and cyclodextrin and cast onto the base membrane. Then, an organic phase solution containing acyl chloride compounds is cast, and a composite (separation) layer is prepared through interfacial polymerization. Finally, the cyclodextrin-modified composite organic solvent nanofiltration membrane is obtained by vacuum drying. This membrane is particularly suitable for nanofiltration of alcohols and alkane organic solvents, and by changing the preparation conditions, the permeate flux and retention performance of the membrane can be controlled to meet the requirements of practical applications. In recent years, multilayer thin-layer composite membranes with intermediate layers have been developed to further regulate membrane structure and improve membrane performance.

[0004] The paper "Sub–10nm polyamide nanofilms with ultrafast solvent transport formolecular separation" (Science, 2015, 348(6241): 1347-1351) discloses a method for preparing a thin-film composite nanofiltration membrane with an ultrathin polyamide layer by depositing a cadmium hydroxide sacrificial layer on the surface of a base membrane and then performing interfacial polymerization. Although the membrane exhibits a very high flux, removing the sacrificial layer weakens the interaction between the separation layer and the support layer, reducing the structural stability of the nanofiltration membrane.

[0005] The paper "Ultra-permeable polyamide membranes harvested by covalent organic framework nanofiber scaffolds: a two-in-one strategy" (Chemical Science, 2019, 10(39): 9077-9083) discloses the preparation of thin-layer nanocomposite membranes on polyethersulfone ultrafiltration base membranes using COF materials as interlayers. This membrane exhibits high flux and high rejection rate. However, the bonding force between pure COF materials as interlayers and the base membrane and separation layer is weak, which easily leads to structural damage to the thin-layer composite nanofiltration membrane. Furthermore, the preparation of COF materials is costly and the process is complex.

[0006] Because organic solvents have larger molecular structures and higher viscosity than water, traditional asymmetric membranes and thin-layer composite membranes exhibit lower permeate fluxes when used for organic solvent nanofiltration. While introducing an intermediate layer into a thin-layer composite membrane can further modulate the membrane structure and improve flux, it typically suffers from weak bonding between the intermediate layer and the support layer, and between the intermediate layer and the separation layer.

[0007] Therefore, there is an urgent need to research and develop an organic solvent nanofiltration membrane with high flux, good separation performance, high stability, and simple preparation process. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of low flux and weak interaction between the intermediate layer and the support layer in existing composite nanofiltration membranes, leading to poor separation performance and instability. This invention provides a composite nanofiltration membrane, its preparation method, and its application. The support layer of this composite nanofiltration membrane is a polymer layer containing nano-manganese dioxide. The nano-manganese dioxide is uniformly dispersed in the polymer layer and interacts with the tannic acid in the intermediate layer. This interaction provides channels for solvent transport through the gaps between the nano-manganese dioxide and the polymer matrix, reducing resistance to solvent passage and increasing flux. Simultaneously, the interaction between the intermediate layer and the separation layer results in a thinner separation layer, further improving the flux of the composite nanofiltration membrane.

[0009] To achieve the above objectives, the first aspect of the present invention provides a composite nanofiltration membrane, wherein the composite nanofiltration membrane includes a reinforcing layer and a support layer, an intermediate layer and a separation layer sequentially attached to the surface of the reinforcing layer;

[0010] The support layer is a polymer layer containing nano-manganese dioxide;

[0011] The intermediate layer is a tannic acid-iron ion complex layer;

[0012] The separation layer is a polyamide layer.

[0013] A second aspect of the present invention provides a method for preparing a composite nanofiltration membrane, comprising the following steps:

[0014] S1. The dispersion containing nano-manganese dioxide is mixed and dissolved with the polymer to obtain the casting solution;

[0015] S2. Load the casting liquid onto a nonwoven fabric and perform a phase transformation to obtain the support layer substrate-I;

[0016] S3. The support layer substrate-I is first immersed in tannic acid solution, and then second immersed in ferric chloride solution to obtain support layer substrate-II;

[0017] S4. The support layer substrate-II is immersed in a polyamine solution for a third time, and then immersed in a polyacrylamide solution for a fourth time to obtain the initial nanofiltration membrane.

[0018] S5. The initial nanofiltration membrane is subjected to heat treatment to obtain the composite nanofiltration membrane.

[0019] A third aspect of the present invention provides a composite nanofiltration membrane prepared by the preparation method described in the second aspect of the present invention.

[0020] The fourth aspect of the present invention provides an application of the composite nanofiltration membrane described in the first or third aspect of the present invention in the field of separation.

[0021] Through the above technical solutions, the composite nanofiltration membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0022] (1) The support layer of the composite nanofiltration membrane is a polymer layer containing nano-manganese dioxide. The nano-manganese dioxide is uniformly dispersed in the polymer layer. The gap between the nano-manganese dioxide and the polymer matrix provides a channel for solvent transport, reduces the resistance to solvent passage, and increases membrane flux.

[0023] (2) The addition of nano-manganese dioxide to the support layer improves the solvent resistance of the composite nanofiltration membrane. Furthermore, it has high membrane flux and is suitable for use in organic solvents such as alcohols, esters, benzenes, and alkanes.

[0024] (3) There is an interaction between the nano-manganese dioxide in the support layer and the tannic acid in the intermediate layer, which increases the interaction between the support layer and the intermediate layer and improves the flux of the composite nanofiltration membrane. There is an electrostatic interaction between the intermediate layer and the separation layer, which makes the separation layer thinner and further improves the flux of the composite nanofiltration membrane.

[0025] (4) The composite nanofiltration membrane is easy to prepare. Its separation performance is affected by the content of nano-manganese dioxide in the support layer and the formulation process of the intermediate layer and the separation layer. Therefore, it has a wide range of control, is easy to adjust, and expands the application range. Detailed Implementation

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] The first aspect of the present invention provides a composite nanofiltration membrane, wherein the composite nanofiltration membrane includes a reinforcing layer and a support layer, an intermediate layer and a separation layer sequentially attached to the surface of the reinforcing layer;

[0028] The support layer is a polymer layer containing nano-manganese dioxide;

[0029] The intermediate layer is a tannic acid-iron ion complex layer;

[0030] The separation layer is a polyamide layer.

[0031] In this invention, the composite nanofiltration membrane comprises a reinforcing layer and a support layer, an intermediate layer, and a separation layer sequentially attached to the surface of the reinforcing layer. The intermediate layer provides excellent bonding between the support layer and the separation layer, resulting in superior stability of the composite nanofiltration membrane. Furthermore, the presence of nano-manganese dioxide gives the support layer a specific porosity, ensuring high membrane flux. In the intermediate layer, the complex of tannic acid and iron ions forms special channels, reducing the pore size of the support layer. This prevents the separation layer, prepared during interfacial polymerization, from embedding into the support layer, which would otherwise reduce flux and further improve the rejection rate of Sudan III.

[0032] According to the present invention, in the support layer, the mass ratio of nano-manganese dioxide to polymer is 1-50:100.

[0033] According to the present invention, the mass ratio of the nano-manganese dioxide to the polymer satisfies the above-mentioned range, which enables the nano-manganese dioxide to be uniformly dispersed in the polymer matrix and form a specific pore structure, thereby reducing the resistance to solvent passage and increasing the throughput.

[0034] Furthermore, in the support layer, the mass ratio of the nano-manganese dioxide to the polymer is 10-30:100.

[0035] According to the present invention, the average particle size of the manganese dioxide is 20-80 nm.

[0036] In this invention, the average particle size of the manganese dioxide meets the above-mentioned range, which enables the formation of a polymer support layer with well-dispersed nano-manganese dioxide.

[0037] Furthermore, the average particle size of the manganese dioxide is 30-60 nm.

[0038] According to the present invention, the polymer is selected from at least one of polyimide, polyetherimide, cross-linked polyimide, cross-linked polyetherimide, polyacrylonitrile, and polyarylamide.

[0039] According to the present invention, the material constituting the reinforcing layer is selected from polyolefin nonwoven fabric and / or polyester nonwoven fabric.

[0040] In this invention, the polyolefin nonwoven fabric and / or polyester nonwoven fabric can both be obtained commercially.

[0041] According to the present invention, the thickness of the support layer is 20-100 μm, preferably 30-60 μm.

[0042] According to the present invention, the support layer has a porous structure, wherein the porosity of the support layer is 30-80%.

[0043] In this invention, the porosity of the support layer meets the above-mentioned range, which enables the support layer to have a specific pore structure and improve membrane flux.

[0044] Furthermore, the porosity of the support layer is 50-70%.

[0045] According to the present invention, the average pore size of the support layer is 10-100 nm, preferably 30-80 nm.

[0046] According to the present invention, the thickness of the intermediate layer is 20-100 nm, preferably 30-60 nm.

[0047] According to the present invention, the average pore size of the intermediate layer is 10-50 nm, preferably 15-30 nm.

[0048] According to the present invention, the thickness of the separation layer is 20-150 nm.

[0049] In this invention, the thickness of the separation layer meets the above-mentioned range, which enables the flux of the composite nanofiltration membrane to be further improved.

[0050] Furthermore, the thickness of the separation layer is 50-100 nm.

[0051] According to the present invention, the average pore size of the separation layer is 0.15-0.5 nm, preferably 0.2-0.3 nm.

[0052] According to the present invention, the polyamide separation layer is obtained by interfacial polymerization of polyamine solution and polyacrylamide solution on the surface of tannic acid iron ion complex intermediate layer.

[0053] According to the present invention, the polyamine compound is selected from at least one of m-phenylenediamine, p-phenylenediamine, piperazine, polyethyleneimine, and polyethylene polyamine.

[0054] According to the present invention, the polyacrylamide chloride compound is selected from at least one of pyromellitic chloride, isophthaloyl chloride and terephthaloyl chloride.

[0055] According to the present invention, the degree of crosslinking of the separation layer is ≥70%, preferably ≥80%.

[0056] In this invention, each amine-containing group in the polyacrylamide compound reacts with the polyamine compound to form a cross-linked polyamide structure. In the separation layer, the content of structural units from the polyamine compound is 20-50 wt%, and the content of structural units from the polyacrylamide compound is 50-80 wt%. This can be determined by NMR, IR, and XPS spectral analysis, or calculated based on the difference between the amount of material added and the amount remaining during the preparation of the separation layer.

[0057] According to the present invention, the ethanol flux of the composite nanofiltration membrane is ≥1.5 Lm. -2 h -1 bar -1 n-Hexane flux ≥ 0.3 Lm - 2 h -1 bar -1 Sudan III interception rate ≥90%.

[0058] A second aspect of the present invention provides a method for preparing a composite nanofiltration membrane, comprising the following steps:

[0059] S1. The dispersion containing nano-manganese dioxide is mixed and dissolved with the polymer to obtain the casting solution;

[0060] S2. Load the casting liquid onto a nonwoven fabric and perform a phase transformation to obtain the support layer substrate-I;

[0061] S3. The support layer substrate-I is first immersed in tannic acid solution, and then second immersed in ferric chloride solution to obtain support layer substrate-II;

[0062] S4. The support layer substrate-II is immersed in a polyamine solution for a third time, and then immersed in a polyacrylamide solution for a fourth time to obtain the initial nanofiltration membrane.

[0063] S5. The initial nanofiltration membrane is subjected to heat treatment to obtain the composite nanofiltration membrane.

[0064] In this invention, the preparation method of the composite nanofiltration membrane is simple. Tannic acid contains a large number of phenolic hydroxyl groups and ester groups, which can complex with iron ions and form hydrogen bonds with oxygen atoms in the nano-manganese dioxide in the support layer, as well as interact with amine groups in the separation layer. Therefore, the overall stability of the composite nanofiltration membrane is improved.

[0065] In this invention, when the polymer in step S1 is selected from polyimide and / or polyetherimide, in order to further improve the solvent resistance of the prepared mixed matrix nanofiltration membrane, the support layer substrate-I can be further crosslinked by immersing it in an alcohol solution of hexamethylenediamine.

[0066] According to the present invention, in step S1, the dispersion contains nano-manganese dioxide and a first solvent.

[0067] In this invention, the dispersion containing nano-manganese dioxide can be prepared in accordance with conventional methods in the art. In this invention, the dispersion containing nano-manganese dioxide is obtained by ultrasonically dispersing nano-manganese dioxide in a solvent.

[0068] In this invention, the ultrasonic dispersion time is 30-180 min and the temperature is 20-30℃.

[0069] In this invention, the mixing is carried out by stirring, and there are no particular limitations on the stirring conditions, as long as the polymer can be dissolved. For example, in this invention, the stirring time is 5-48 hours and the temperature is 50-100°C.

[0070] According to the present invention, the first solvent is selected from at least one of N,N-dimethylformamide (DMF), N-methylpyrrolidone, N,N-dimethylacetamide (DMAc), dimethyl sulfoxide, tetrahydrofuran, dioxane, acetonitrile, acetone and chloroform.

[0071] According to the present invention, the solid content of the casting solution is 12-28 wt%.

[0072] In this invention, the solid content of the casting solution meets the above-mentioned range, which can form a support layer with a smooth, uniform surface and a certain strength.

[0073] Furthermore, the solid content of the casting solution is 15-25 wt%.

[0074] According to the present invention, the mass ratio of the nano-manganese dioxide to the polymer is 1-50:100.

[0075] In this invention, the mass ratio of the nano-manganese dioxide and the polymer satisfies the above-mentioned range, which can obtain a support layer with specific pore structure and porosity, thereby improving membrane separation performance.

[0076] Furthermore, the mass ratio of the nano-manganese dioxide to the polymer is 10-30:100.

[0077] According to the present invention, the polymer is selected from at least one of polyimide, polyetherimide, cross-linked polyimide, cross-linked polyetherimide, polyacrylonitrile, and polyarylamide.

[0078] According to the present invention, in step S2, the casting solution is scraped onto a nonwoven fabric and immersed in a coagulation bath to carry out the phase transformation, wherein the solvent used in the coagulation bath is a poor solvent for the polymer.

[0079] In this invention, the unsuitable solvent for the polymer can be water.

[0080] According to the present invention, in step S3, the mass concentration of tannic acid in the tannic acid solution is 0.05-0.5 wt%.

[0081] Furthermore, the mass concentration of tannic acid in the tannic acid solution is 0.1-0.3 wt%.

[0082] According to the present invention, the mass concentration of ferric chloride in the ferric chloride solution is 0.1-2%.

[0083] Furthermore, the mass concentration of ferric chloride in the ferric chloride solution is 0.5-1 wt%.

[0084] In this invention, the mass concentrations of tannic acid and ferric chloride meet the above-mentioned range, which enables tannic acid to fully complex with iron ions, strengthens the interaction between tannic acid and nano-manganese dioxide, and enhances the electrostatic interaction with amino groups in the separation layer, thereby improving the overall separation performance of the composite nanofiltration membrane in the solvent.

[0085] According to the present invention, the conditions for the first soaking and the second soaking each independently include: a temperature of 20-50°C and a time of 0.5-30 min.

[0086] According to the present invention, in step S4, the polyamine solution comprises a polyamine compound and water.

[0087] According to the present invention, in the polyamine solution, the amount of the polyamine compound used is 0.1-10g, preferably 0.2-2g, relative to 100mL of water.

[0088] According to the present invention, the polyamine compound is selected from at least one of m-phenylenediamine, p-phenylenediamine, piperazine, polyethyleneimine, and polyethylene polyamine.

[0089] According to the present invention, the polyacryl chloride solution comprises a polyacryl chloride compound and a second solvent;

[0090] According to the present invention, in the polyacrylamide chloride solution, the amount of the polyacrylamide chloride compound used is 0.01-1g, preferably 0.05-0.5g, relative to 100mL of the second solvent.

[0091] According to the present invention, the polyacrylamide chloride compound is selected from at least one of pyromellitic chloride, isophthaloyl chloride and terephthaloyl chloride.

[0092] According to the present invention, the second solvent is immiscible with water.

[0093] In this invention, the second solvent is able to dissolve polyacrylamide compounds without being miscible with water, so that polyamines and polyacrylamides can react better at the interface of the two solvents to form a thin film.

[0094] In this invention, the second solvent is selected from at least one of n-hexane, n-heptane, or isoalkanes.

[0095] According to a preferred embodiment of the present invention, the isoalkane is selected from at least one of Isopar E, Isopar G and Isopar H.

[0096] According to the present invention, the conditions for the third immersion and the fourth immersion each independently include: a temperature of 20-50°C and a time of 10-300s.

[0097] According to the present invention, the conditions for the heat treatment include: a temperature of 40-80°C and a time of 2-10 min.

[0098] In this invention, the heat treatment satisfies the above-mentioned range and can further increase the crosslinking degree of the polyamide obtained by the reaction of polyamine and polyacryl chloride.

[0099] A third aspect of the present invention provides a composite nanofiltration membrane prepared by the preparation method described in the second aspect of the present invention.

[0100] The fourth aspect of the present invention provides an application of the composite nanofiltration membrane described in the first or third aspect of the present invention in the field of separation.

[0101] The present invention will be described in detail below through embodiments.

[0102] In the following examples, the average particle size of nano-manganese dioxide was measured using a particle size analyzer;

[0103] Porosity was measured by gravimetric method;

[0104] The average pore size of the substrate layer and the intermediate layer was measured using an ultrafiltration membrane pore size analyzer (PSMA-10, Nanjing Gaoqian Functional Materials Technology Co., Ltd.);

[0105] Thickness was observed using a scanning electron microscope;

[0106] The degree of crosslinking reaction (DC) of the composite membrane separation layer is characterized by testing the fine oxygen spectrum of the membrane surface using X-ray photoelectron spectroscopy (XPS). This is obtained by calculating the content of O=C-N and O=C-O groups according to Formula I. By fitting the multiple peaks of the fine spectrum into a single peak, the peak area of ​​each peak is calculated, representing the content of that group. In Formula I, C... –CON< For the peak area of ​​O = C - N, C –COO– This represents the peak area of ​​O = C - O.

[0107]

[0108] The content of each structural unit in the separated layer was calculated by subtracting the amount of residual monomer in the solution after the reaction from the amount of the corresponding monomer added before the reaction. The amount of residual monomer in the solution after the reaction was determined by gas chromatography.

[0109] Membrane separation performance was measured using dead-end filtration, under the following conditions: temperature 25℃, pressure 2MPa, and stirring speed 500rpm. The concentration of Sudan III ethanol solution was calculated using an ultraviolet-visible spectrophotometer at a wavelength of 505nm via absorbance versus concentration curves.

[0110] Polyimide, purchased from Evonik, brand name P84.

[0111] Polyetherimide, purchased from SABIC Innovative Plastics (China) Co., Ltd., brand name Ultem 1000;

[0112] Nano-manganese dioxide, purchased from Shanghai Naio Nanotechnology Co., Ltd., with an average particle size of 50nm;

[0113] Nano-silica, purchased from Shenzhen Jingcai Chemical Co., Ltd., with an average particle size of 50nm;

[0114] Tannic acid, ferric chloride, m-phenylenediamine, and trimesoyl chloride were purchased from Bailingwei Technology Co., Ltd.; other chemical reagents were purchased from Beijing Innocare Technology Co., Ltd.

[0115] Example 1

[0116] S1. Add 5g of nano-manganese dioxide to 75g of DMAc, ultrasonically disperse at 25℃ for 60min, then add 20g of polyetherimide, heat to 60℃ and stir for 6h to dissolve the polyetherimide, thus obtaining the casting solution.

[0117] S2. Use a doctor blade to scrape the casting solution onto the polypropylene nonwoven fabric, and then immerse it in a deionized water coagulation bath to complete the phase transformation and obtain the support layer substrate-I.

[0118] S3. The support layer substrate-I is first soaked in a tannic acid solution (25°C) consisting of 0.2g of tannic acid and 100g of water for 5 minutes, then the excess aqueous phase is removed, and then it is soaked in a ferric chloride solution (25°C) consisting of 0.6g of ferric chloride and 100g of water for 5 minutes. Finally, it is washed with deionized water to obtain the support layer substrate-II.

[0119] S4. The support layer substrate-II is immersed for a third time in a solution consisting of 2g of m-phenylenediamine and 100g of water for 2min. Then, the excess aqueous phase is removed, and the substrate is immersed for a fourth time in a solution consisting of 0.1g of trimesoyl chloride and 100mL of hexane for 2min to obtain the initial nanofiltration membrane.

[0120] S5. The initial nanofiltration membrane is heated at 70°C for 5 minutes to obtain the composite nanofiltration membrane M1.

[0121] The separation performance of the composite nanofiltration membrane M1 was tested, and the result showed a flux of 2.6 L / m³ for ethanol. -2 h -1 bar -1 The Sudan III rejection rate was 95.5%, and the n-hexane flux was 0.52 L m. -2 h -1 bar -1 .

[0122] Example 2

[0123] S1. Add 5g of nano-manganese dioxide to 75g of DMAc, ultrasonically disperse at 25℃ for 60min, then add 20g of polyetherimide, heat to 60℃ and stir for 6h to dissolve the polyetherimide, thus obtaining the casting solution.

[0124] S2. Use a doctor blade to scrape the casting solution onto the polypropylene nonwoven fabric, then immerse it in a deionized water coagulation bath to complete the phase transformation, and then soak it in a solution composed of 5g hexamethylenediamine and 100g methanol for 6 hours to obtain the support layer substrate-I.

[0125] S3. The support layer substrate-I is first soaked in a tannic acid solution (25°C) consisting of 0.2g of tannic acid and 100g of water for 5 minutes, then the excess aqueous phase is removed, and then it is soaked in a ferric chloride solution (25°C) consisting of 0.6g of ferric chloride and 100g of water for 5 minutes. Finally, it is washed with deionized water to obtain the support layer substrate-II.

[0126] S4. The support layer substrate-II is immersed for a third time in a solution consisting of 2g of m-phenylenediamine and 100g of water for 2min. Then, the excess aqueous phase is removed, and the substrate is immersed for a fourth time in a solution consisting of 0.1g of trimesoyl chloride and 100mL of hexane for 2min to obtain the initial nanofiltration membrane.

[0127] S5. The initial nanofiltration membrane is heated at 70°C for 5 minutes to obtain the composite nanofiltration membrane M2.

[0128] The composite nanofiltration membrane M2 has a flux of 2.2 L / m³ for ethanol. -2 h -1 bar -1 The Sudan III rejection rate was 96.4%, and the n-hexane flux was 0.47 L m. -2 h -1 bar -1 .

[0129] Example 3

[0130] S1. Add 6g of nano-manganese dioxide (average particle size 70nm) to 74g of DMF, ultrasonically disperse at 25℃ for 50min, then add 20g of polyimide, heat to 70℃ and stir for 5h to dissolve the polyimide to obtain the casting solution.

[0131] S2. Use a doctor blade to scrape the casting solution onto the polypropylene nonwoven fabric, and then immerse it in a deionized water coagulation bath to complete the phase transformation and obtain the support layer substrate-I.

[0132] S3. The support layer substrate-I is first soaked in a tannic acid solution (25°C) consisting of 0.3g of tannic acid and 100g of water for 3 minutes, then the excess aqueous phase is removed, and the support layer substrate-II is second soaked in a ferric chloride solution (25°C) consisting of 0.9g of ferric chloride and 100g of water for 3 minutes. Finally, it is washed with deionized water to obtain the support layer substrate-II.

[0133] S4. The obtained support layer substrate-II is immersed for a third time for 2 minutes in a solution consisting of 3g of p-phenylenediamine and 100g of water. Then, the excess aqueous phase is removed, and the substrate is immersed for a fourth time for 2 minutes in a solution consisting of 0.5g of trimesoyl chloride and 100mL of hexane to obtain the initial nanofiltration membrane.

[0134] S5. Finally, the initial nanofiltration membrane is heated at 70°C for 5 minutes to obtain the composite nanofiltration membrane M3.

[0135] The composite nanofiltration membrane M3 has a flux of 2.5 L / m³ for ethanol. -2 h -1 bar -1 The Sudan III rejection rate was 91.2%, and the n-hexane flux was 0.52 L m. -2 h -1 bar -1 .

[0136] Example 4

[0137] S1. Add 8g of nano-manganese dioxide to 76g of DMF, ultrasonically disperse at 25℃ for 60min, then add 16g of polyacrylonitrile (weight average molecular weight of 85000g / mol), heat to 60℃ and stir for 6h to dissolve the polyacrylonitrile, thus obtaining the casting solution.

[0138] S2. Use a doctor blade to scrape the casting solution onto the polyester nonwoven fabric, and then immerse it in a deionized water coagulation bath to complete the phase transformation and obtain the support layer substrate-I.

[0139] S3. The support layer substrate-I is first soaked in a tannic acid solution (25°C) consisting of 0.05g of tannic acid and 100g of water for 10 minutes, then the excess aqueous phase is removed, and the support layer substrate-II is second soaked in a ferric chloride solution (25°C) consisting of 0.1g of ferric chloride and 100g of water for 10 minutes. Finally, it is washed with deionized water to obtain the support layer substrate-II.

[0140] S4. The support layer substrate-II is immersed for a third time in a solution consisting of 2g of m-phenylenediamine and 100g of water for 2min. Then, the excess aqueous phase is removed, and the substrate is immersed for a fourth time in a solution consisting of 0.1g of trimesoyl chloride and 100mL of hexane for 2min to obtain the initial nanofiltration membrane.

[0141] S5. The initial nanofiltration membrane is heated at 70°C for 5 minutes to obtain the composite nanofiltration membrane M4.

[0142] The composite nanofiltration membrane M4 has a flux of 2.1 L / m³ for ethanol. -2 h -1 bar -1 The Sudan III rejection rate was 93.8%, and the n-hexane flux was 0.46 L m. -2 h -1 bar -1 .

[0143] Example 5

[0144] S1. Add 0.2g of nano-manganese dioxide to 79.8g of DMF, ultrasonically disperse at 25℃ for 60min, then add 20g of polyimide, heat to 60℃ and stir for 6h to dissolve the polyimide, thus obtaining the casting solution.

[0145] S2. Use a doctor blade to scrape the casting solution onto the polypropylene nonwoven fabric, and then immerse it in a deionized water coagulation bath to complete the phase transformation and obtain the support layer substrate-I.

[0146] S3. The support layer substrate-I is first soaked in a tannic acid solution (25°C) consisting of 0.5g of tannic acid and 100g of water for 2 minutes, then the excess aqueous phase is removed, and then it is soaked in a ferric chloride solution (25°C) consisting of 2g of ferric chloride and 100g of water for 2 minutes. Finally, it is washed with deionized water to obtain the support layer substrate-II.

[0147] S4. The support layer substrate-II is immersed for a third time in a solution consisting of 2g of m-phenylenediamine and 100g of water for 2min. Then, the excess aqueous phase is removed, and the substrate is immersed for a fourth time in a solution consisting of 0.1g of trimesoyl chloride and 100mL of hexane for 2min to obtain the initial nanofiltration membrane.

[0148] S5. The initial nanofiltration membrane is heated at 70°C for 5 minutes to obtain the composite nanofiltration membrane M5.

[0149] The composite nanofiltration membrane M5 has a flux of 1.9 L / m³ for ethanol. -2 h -1 bar -1 The Sudan III rejection rate was 90.6%, and the n-hexane flux was 0.42 L m. -2 h -1 bar -1 .

[0150] Example 6

[0151] Following the method of Example 2, except that the amount of nano-manganese dioxide used was 2.4g, the amount of DMAc used was 88g, and the amount of polyetherimide used was 9.6g, resulting in a solid content of 12wt% in the casting solution. A composite nanofiltration membrane M6 was obtained.

[0152] The flux of the composite nanofiltration membrane M6 for ethanol is 2.8 L / m³. -2 h -1 bar -1 The Sudan III rejection rate was 91.5%, and the n-hexane flux was 0.73 L m. -2 h -1 bar -1 .

[0153] Example 7

[0154] The method of Example 2 was followed, except that the amount of nano-manganese dioxide used was 1g, the amount of DMAc used was 88g, and the amount of polyetherimide used was 11g, so that the solid content of the casting solution was 12wt%. A composite nanofiltration membrane M7 was obtained.

[0155] The flux of the composite nanofiltration membrane M7 for ethanol is 2.6 L / m³. -2 h -1 bar -1The Sudan III rejection rate was 92%, and the n-hexane flux was 0.66 L m. -2 h -1 bar -1 .

[0156] Example 8

[0157] Following the method of Example 2, except that the particle size of the nano-manganese dioxide was 90 nm. A composite nanofiltration membrane M8 was obtained.

[0158] The flux of the composite nanofiltration membrane M8 for ethanol is 1.5 L / m³. -2 h -1 bar -1 The Sudan III rejection rate was 90.2%, and the n-hexane flux was 0.35 L m. -2 h -1 bar -1 .

[0159] Example 9

[0160] Following the method of Example 2, except that the amount of tannic acid used was 0.05 g and the amount of ferric chloride used was 0.05 g. A composite nanofiltration membrane M9 was obtained.

[0161] The flux of the composite nanofiltration membrane M9 for ethanol is 1.8 L / m³. -2 h -1 bar -1 The Sudan III rejection rate was 89.3%, and the n-hexane flux was 0.41 L m. -2 h -1 bar -1 .

[0162] Example 10

[0163] Following the method of Example 2, except that the amount of m-phenylenediamine used was 10g and the amount of trimesoyl chloride used was 1g. A composite nanofiltration membrane M10 was obtained.

[0164] The flux of the composite nanofiltration membrane M10 for ethanol is 2.5 L / m³. -2 h -1 bar -1 The Sudan III rejection rate was 94.1%, and the n-hexane flux was 0.53 L m. -2 h -1 bar -1 .

[0165] Comparative Example 1

[0166] S1. Add 20g of polyetherimide to 80g of DMAc, heat to 60℃ and stir for 6h to dissolve the polymer and obtain the casting solution.

[0167] S2. Use a doctor blade to scrape the casting solution onto the polyolefin nonwoven fabric, and then immerse it in a deionized water coagulation bath to complete the phase transformation and obtain the support layer substrate-I.

[0168] S3. The support layer substrate-II is immersed for a third time in a solution consisting of 2g of m-phenylenediamine and 100g of water for 2min. Then, the excess aqueous phase is removed, and the substrate is immersed for a fourth time in a solution consisting of 0.1g of trimesoyl chloride and 100mL of hexane for 2min to obtain the initial nanofiltration membrane.

[0169] S4. The initial nanofiltration membrane is heated at 70°C for 5 minutes to obtain the composite nanofiltration membrane CM1.

[0170] The flux of the composite nanofiltration membrane CM1 for ethanol is 0.31 L / m³. -2 h -1 bar -1 The Sudan III rejection rate was 89.6%, and the n-hexane flux was 0.1 L m. -2 h -1 bar -1 .

[0171] Comparative Example 2

[0172] The method is the same as in Example 1, except that step S3 is not performed, meaning that the final composite nanofiltration membrane CM2 does not contain an intermediate layer.

[0173] The flux of the composite nanofiltration membrane CM2 for ethanol is 0.57 L / m². -2 h -1 bar -1 The Sudan III rejection rate was 90.4%, and the n-hexane flux was 0.18 L m. -2 h -1 bar -1 .

[0174] Comparative Example 3

[0175] Following the method of Example 1, except that nano-manganese dioxide was not included, a composite nanofiltration membrane CM3 was obtained.

[0176] The flux of the composite nanofiltration membrane CM3 for ethanol is 0.51 L / m³. -2 h -1 bar -1 The Sudan III rejection rate was 85.3%, and the n-hexane flux was 0.15 L m. -2 h -1 bar -1 .

[0177] Comparative Example 4

[0178] The method of Example 1 was followed, except that nano-manganese dioxide was replaced with nano-silicon dioxide. A composite nanofiltration membrane CM4 was obtained.

[0179] The flux of the composite nanofiltration membrane CM4 for ethanol is 0.62 L / m³. -2 h -1 bar -1 The Sudan III rejection rate was 88.2%, and the n-hexane flux was 0.17 L m. -2 h -1 bar -1 .

[0180] Test case

[0181] The separation performance results of the composite nanofiltration membranes prepared in the examples and comparative examples are shown in Table 1; the porosity, average pore size, and thickness of each layer of the mixed matrix nanofiltration membranes prepared in the examples and comparative examples were tested, and the results are shown in Table 2. The content of the separation layer structural units is shown in Table 3.

[0182] Table 1

[0183]

[0184]

[0185] Table 2

[0186]

[0187] Table 2 (continued)

[0188] serial number Separation layer thickness / nm Average pore size of the separation layer (nm) Degree of crosslinking of the separation layer / % Example 1 126 0.217 82.4 Example 2 139 0.205 85.6 Example 3 130 0.286 73.5 Example 4 135 0.255 78.1 Example 5 143 0.312 70.8 Example 6 121 0.224 75.2 Example 7 128 0.229 77.3 Example 8 154 0.296 71.5 Example 9 167 0.302 68.3 Example 10 116 0.219 80.6 Comparative Example 1 189 0.324 76.8 Comparative Example 2 162 0.293 72.1 Comparative Example 3 179 0.335 67 Comparative Example 4 155 0.318 63.5

[0189] Table 3

[0190] serial number Derived from polyamine structural units (wt%) Derived from polyacrylamide chloride structural units (wt%) Example 1 33 67 Example 2 32 68 Example 3 40 60 Example 4 28 72 Example 5 29 71 Example 6 32 68 Example 7 30 70 Example 8 33 67 Example 9 29 71 Example 10 45 55 Comparative Example 1 25 75 Comparative Example 2 28 72 Comparative Example 3 31 69 Comparative Example 4 30 70

[0191] The results above demonstrate that the organic solvent nanofiltration membrane prepared using the method described in this invention exhibits a significantly improved flux. This is partly due to the introduction of nano-manganese dioxide into the support layer of the organic solvent nanofiltration membrane provided by this invention. The voids between manganese dioxide and the polymer matrix offer additional channels for solvent transport, thus reducing resistance to solvent passage and increasing flux. Furthermore, during the interfacial polymerization process for preparing the separation layer, the electrostatic and hydrogen bonding interactions between the tannic acid and polyamine monomers in the intermediate layer reduce the diffusion rate of amine monomers into the oil phase, resulting in a thinner separation layer and a higher membrane flux.

[0192] Comparing Examples 1 and 5, it can be seen that when the mass ratio of nano-manganese dioxide to polymer is within a more preferred range, the composite nanofiltration membrane exhibits better overall performance in terms of flux and retention. When the polymer mass is too high, the ethanol flux and Sudan III rejection rate decrease significantly.

[0193] Comparing Examples 1 and 8, it can be seen that excessively large nano-manganese dioxide particle size leads to a significant decrease in hexane flux. Comparing Examples 1 and 9, it can be seen that excessively low concentrations of tannic acid and iron salts result in a decrease in the cross-linking degree of the separation layer, thereby affecting the overall performance of the composite nanofiltration membrane.

[0194] In Comparative Example 1, the absence of nano-manganese dioxide and the absence of the tannic acid-iron ion complex layer in Comparative Example 2 resulted in a significant decrease in ethanol and n-hexane fluxes, as well as a slight decrease in the rejection rate of Sudan III.

[0195] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composite nanofiltration membrane, characterized by, The composite nanofiltration membrane includes a reinforcing layer and a support layer, an intermediate layer, and a separation layer sequentially attached to the surface of the reinforcing layer. The support layer is a polymer layer containing nano-manganese dioxide; The intermediate layer is a tannic acid-iron ion complex layer; The separation layer is a polyamide layer, which is obtained by interfacial polymerization of a polyamine solution and a polyacrylamide chloride solution on the surface of a tannic acid iron ion complex intermediate layer. The polyamine compound in the polyamine solution is selected from at least one of m-phenylenediamine, p-phenylenediamine, piperazine, polyethyleneimine, and polyethylene polyamine.

2. The composite nanofiltration membrane according to claim 1, wherein, In the support layer, the mass ratio of nano-manganese dioxide to polymer is 1-50:

100.

3. The composite nanofiltration membrane according to claim 2, wherein, In the support layer, the mass ratio of nano-manganese dioxide to polymer is 10-30:

100.

4. The composite nanofiltration membrane according to claim 1, wherein, The average particle size of the nano-manganese dioxide is 20-80 nm.

5. The composite nanofiltration membrane according to claim 4, wherein, The average particle size of the nano-manganese dioxide is 30-60 nm.

6. The composite nanofiltration membrane according to claim 1, wherein, The polymer is selected from at least one of polyimide, polyetherimide, cross-linked polyimide, cross-linked polyetherimide, polyacrylonitrile, and polyarylamide.

7. The composite nanofiltration membrane according to claim 1, wherein, The material constituting the reinforcing layer is selected from polyolefin nonwoven fabric and / or polyester nonwoven fabric.

8. The composite nanofiltration membrane according to claim 1, wherein, The thickness of the support layer is 20-100 μm.

9. The composite nanofiltration membrane according to claim 8, wherein, The thickness of the support layer is 30-60 μm.

10. The composite nanofiltration membrane according to claim 1, wherein, The support layer has a porous structure, wherein the porosity of the support layer is 30-80%.

11. The composite nanofiltration membrane according to claim 10, wherein, The porosity of the support layer is 50-70%.

12. The composite nanofiltration membrane according to claim 1, wherein, The average pore size of the support layer is 10-100 nm.

13. The composite nanofiltration membrane according to claim 12, wherein, The average pore size of the support layer is 30-80 nm.

14. The composite nanofiltration membrane according to claim 1, wherein, The thickness of the intermediate layer is 20-100 nm.

15. The composite nanofiltration membrane according to claim 14, wherein, The thickness of the intermediate layer is 30-60 nm.

16. The composite nanofiltration membrane according to claim 1, wherein, The average pore size of the intermediate layer is 10-50 nm.

17. The composite nanofiltration membrane according to claim 16, wherein, The average pore size of the intermediate layer is 15-30 nm.

18. The composite nanofiltration membrane according to claim 1, wherein, The thickness of the separation layer is 20-150 nm.

19. The composite nanofiltration membrane according to claim 18, wherein, The thickness of the separation layer is 50-100 nm.

20. The composite nanofiltration membrane according to claim 1, wherein, The average pore size of the separation layer is 0.15-0.5 nm.

21. The composite nanofiltration membrane according to claim 20, wherein, The average pore size of the separation layer is 0.2-0.3 nm.

22. The composite nanofiltration membrane according to claim 1, wherein, The polyacryl chloride compound is selected from at least one of pyromellitic chloride, isophthaloyl chloride, and terephthaloyl chloride.

23. The composite nanofiltration membrane according to claim 1, wherein, The degree of crosslinking of the separation layer is ≥70%.

24. The composite nanofiltration membrane according to claim 23, wherein, The degree of crosslinking of the separation layer is ≥80%.

25. A method for preparing a composite nanofiltration membrane according to any one of claims 1-24, characterized in that, Includes the following steps: S1. The dispersion containing nano-manganese dioxide is mixed and dissolved with the polymer to obtain the casting solution; S2. Load the casting liquid onto a nonwoven fabric and perform a phase transformation to obtain the support layer substrate-I; S3. The support layer substrate-I is first immersed in tannic acid solution, and then second immersed in ferric chloride solution to obtain support layer substrate-II; S4. The support layer substrate-II is immersed in a polyamine solution for a third time, and then immersed in a polyacrylamide solution for a fourth time to obtain the initial nanofiltration membrane. S5. The initial nanofiltration membrane is subjected to heat treatment to obtain the composite nanofiltration membrane.

26. The preparation method according to claim 25, wherein, In step S1, the dispersion contains nano-manganese dioxide and a first solvent.

27. The preparation method according to claim 26, wherein, The first solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, dioxane, acetonitrile, acetone and chloroform.

28. The preparation method according to claim 25, wherein, The solid content of the casting solution is 12-28 wt%.

29. The preparation method according to claim 28, wherein, The solid content of the casting solution is 15-25 wt%.

30. The preparation method according to claim 25, wherein, The mass ratio of the nano-manganese dioxide to the polymer is 1-50:

100.

31. The preparation method according to claim 30, wherein, The mass ratio of the nano-manganese dioxide to the polymer is 10-30:

100.

32. The preparation method according to claim 25, wherein, The polymer is selected from at least one of polyimide, polyetherimide, cross-linked polyimide, cross-linked polyetherimide, polyacrylonitrile, and polyarylamide.

33. The preparation method according to claim 25, wherein, In step S2, the casting solution is scraped onto a nonwoven fabric and immersed in a coagulation bath to carry out the phase transformation, wherein the solvent used in the coagulation bath is a poor solvent for the polymer.

34. The preparation method according to claim 25, wherein, The conditions for the first soaking and the second soaking each independently include: a temperature of 20-50℃ and a time of 0.5-30 min.

35. The preparation method according to claim 25, wherein, In step S4, the polyamine solution comprises a polyamine compound and water.

36. The preparation method according to claim 35, wherein, In the polyamine solution, the amount of the polyamine compound used is 0.1-10g relative to 100mL of water.

37. The preparation method according to claim 36, wherein, In the polyamine solution, the amount of the polyamine compound used is 0.2-2g relative to 100mL of water.

38. The preparation method according to claim 25, wherein, The polyacryl chloride solution comprises a polyacryl chloride compound and a second solvent.

39. The preparation method according to claim 38, wherein, In the polyacryl chloride solution, the amount of the polyacryl chloride compound used is 0.01-1g relative to 100mL of the second solvent.

40. The preparation method according to claim 39, wherein, In the polyacryl chloride solution, the amount of the polyacryl chloride compound used is 0.05-0.5g relative to 100mL of the second solvent.

41. The preparation method according to claim 38, wherein, The polyacryl chloride compound is selected from at least one of pyromellitic chloride, isophthaloyl chloride, and terephthaloyl chloride.

42. The preparation method according to claim 38, wherein, The second solvent is not miscible with water.

43. The preparation method according to claim 42, wherein, The second solvent is selected from at least one of n-hexane, n-heptane, or isoalkanes.

44. The preparation method according to claim 25, wherein, The conditions for the third and fourth soakings each independently include: a temperature of 20-50°C and a time of 10-300 seconds.

45. The preparation method according to claim 25, wherein, The heat treatment conditions include: a temperature of 40-80℃ and a time of 2-10 minutes.

46. ​​A composite nanofiltration membrane prepared by the preparation method according to any one of claims 25-45.

47. The application of a composite nanofiltration membrane according to any one of claims 1-24 and 46 in the field of separation.

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