Composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of membrane separation, and discloses a composite nanofiltration membrane as well as a preparation method and application thereof. The composite nanofiltration membrane comprises an enhancement layer, and a support layer, a middle layer and a separation layer which are sequentially attached to the surface of the enhancement layer, the supporting layer is a polymer layer containing nano manganese dioxide; the middle layer is a tannic acid-iron ion complex layer; and the separation layer is a polyamide layer. The supporting 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 and interacts with tannic acid in the middle layer, and gaps between the nano-manganese dioxide and a polymer matrix can provide channels for solvent transmission, reduce solvent passing resistance and improve flux. Meanwhile, the middle layer and the separation layer interact with each other, 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] The present invention relates to the technical field of membrane separation, and in particular to a composite nanofiltration membrane and a preparation method and application thereof. Background Art

[0002] Organic solvent nanofiltration is a new green and energy-saving membrane technology for treating organic solvents. It has broad application prospects in the petrochemical, food and medicine industries. Most of the existing commercial organic solvent nanofiltration membranes are integral cortical asymmetric membranes prepared by phase inversion. Due to the thick cortex and large filtration resistance, the flux is low and the operating pressure is high. The thin-layer composite membrane prepared by interfacial polymerization is composed of a thin selective separation layer and a porous support layer substrate. Since the two can be regulated separately to achieve better overall performance, it has become a research hotspot for many scholars at home and abroad.

[0003] CN104128102A discloses a cyclodextrin modified composite organic solvent nanofiltration composite membrane and a preparation method thereof, wherein the method uses a hydrolysis-modified polyacrylonitrile ultrafiltration membrane as a base membrane, prepares an aqueous phase solution with amine compounds and cyclodextrin and casts it on the base membrane, then casts it with an organic phase solution containing acyl chloride compounds, prepares a composite (separation) layer by interfacial polymerization reaction; and finally obtains a cyclodextrin modified composite organic solvent nanofiltration membrane by vacuum drying. The membrane is particularly suitable for nanofiltration of alcohols and alkane organic solvents, and by changing the preparation conditions, the permeation flux and interception performance of the membrane can be controlled to meet the requirements of practical applications. In recent years, a multi-layer thin-layer composite membrane with an intermediate layer has been developed in order to further regulate the membrane structure and improve the membrane performance.

[0004] "Sub-10nm polyamide nanofilms with ultrafast solvent transport for olecular separation" (Science, 2015, 348(6241): 1347-1351) discloses a thin composite nanofiltration membrane with an ultra-thin polyamide layer prepared by depositing a cadmium hydroxide sacrificial layer on the surface of a base membrane and then performing interfacial polymerization. Although the membrane shows a very large flux, the removal of the sacrificial layer weakens the interaction between the separation layer and the support layer, reducing the structural stability of the nanofiltration membrane.

[0005] "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 use of COF material as an intermediate layer on a polyethersulfone ultrafiltration base membrane to prepare a thin layer of nanocomposite membrane. The membrane has a high flux and a high retention rate, but the binding force between the pure COF material as an intermediate layer and the base membrane and the separation layer is weak, which easily leads to the destruction of the structure of the thin layer composite nanofiltration membrane, and there are problems such as high cost of COF material preparation and complex process.

[0006] Since organic solvents have larger molecular structures and higher viscosity than water, conventional asymmetric membranes and thin-layer composite membranes show lower permeation flux when used for organic solvent nanofiltration. Although introducing an intermediate layer into a thin-layer composite membrane can further regulate the membrane structure and increase the membrane flux, there are usually problems such as 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 the present invention is to overcome the problems of low flux of composite nanofiltration membrane in the prior art, weak interaction between the intermediate layer and the supporting layer, easy peeling, poor separation performance and poor stability, and provide a composite nanofiltration membrane and its preparation method and application. The supporting 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, and there is interaction with tannic acid in the intermediate layer, and can provide a channel for solvent transmission with the gap between the polymer matrix, reduce the resistance of solvent passing, and improve the flux. At the same time, there is interaction between the intermediate layer and the separation layer, so that the thickness of the separation layer is thinner, and the flux of the composite nanofiltration membrane is further improved.

[0009] In order to achieve the above-mentioned object, the first aspect of the present invention provides a composite nanofiltration membrane, wherein the composite nanofiltration membrane comprises a reinforcement layer and a support layer, an intermediate layer and a separation layer sequentially attached to the surface of the reinforcement layer;

[0010] Wherein, the support layer is a polymer layer containing nano manganese dioxide;

[0011] The middle 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, mixing and dissolving a dispersion containing nano manganese dioxide with a polymer to obtain a film casting solution;

[0015] S2, loading the casting solution on a non-woven fabric and performing phase conversion to obtain a support layer substrate-I;

[0016] S3, soaking the support layer substrate-I in a tannic acid solution for a first time, and then soaking it in a ferric chloride solution for a second time to obtain a support layer substrate-II;

[0017] S4, soaking the support layer substrate-II in a polyamine solution for a third time, and then soaking it in a polyacyl chloride solution for a fourth time to obtain an initial nanofiltration membrane;

[0018] S5. Heat-treating the initial nanofiltration membrane to obtain the composite nanofiltration membrane.

[0019] The 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 aspect of the present invention or the third aspect of the present invention in the field of separation.

[0021] Through the above technical scheme, the composite nanofiltration membrane provided by the present invention and its preparation method and application obtain 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 evenly dispersed in the polymer layer. The gap between the nano-manganese dioxide and the polymer matrix provides a channel for solvent transmission, reduces the resistance of solvent passage, and improves membrane flux.

[0023] (2) In the support layer, the addition of nano manganese dioxide can improve the solvent resistance of the composite nanofiltration membrane. The membrane flux is high and it is suitable for use in alcohol, ester, benzene and alkane organic solvents.

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

[0025] (4) The composite nanofiltration membrane preparation method is simple, and the 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, the control range is wide and easy to adjust, thereby expanding the scope of application. DETAILED DESCRIPTION

[0026] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

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

[0028] Wherein, the support layer is a polymer layer containing nano manganese dioxide;

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

[0030] The separation layer is a polyamide layer.

[0031] In the present invention, the composite nanofiltration membrane comprises a reinforcement layer and a support layer, an intermediate layer and a separation layer sequentially attached to the surface of the reinforcement layer, wherein the intermediate layer has a good bonding effect between the support layer and the separation layer, which can make the composite nanofiltration membrane have excellent stability, and due to the presence of nano manganese dioxide, the support layer can have a specific porosity to ensure high membrane flux. In the intermediate layer, the complex of tannic acid and iron ions forms a special pore, which reduces the pore size of the support layer, thereby avoiding the separation layer prepared during interfacial polymerization from being embedded in the support layer, resulting in a decrease in flux, and further improving the retention rate of Sudan III.

[0032] According to the present invention, in the support layer, the mass ratio of the nano manganese dioxide to the 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 range, so that the nano manganese dioxide can be evenly dispersed in the polymer matrix and form a specific pore structure, thereby reducing the resistance of the solvent passing through and improving the flux.

[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 the present invention, the average particle size of the manganese dioxide satisfies the above range, and a polymer support layer in which nano manganese dioxide is well dispersed can be obtained.

[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 polyaramid.

[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 the present invention, the polyolefin non-woven fabric and / or the polyester non-woven fabric can 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 the present invention, the porosity of the support layer satisfies the above range, so that the support layer can have a specific pore structure and improve the 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 the present invention, the thickness of the separation layer satisfies the above range, which can further improve the flux of the composite nanofiltration membrane.

[0050] Furthermore, the separation layer has a thickness of 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 a polyamine solution and a polyacyl chloride solution on the surface of a 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 polyacyl chloride compound is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride.

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

[0056] In the present invention, each amine-containing group in the polyacyl chloride and the polyamine compound can react to form a cross-linked polyamide structure. In the separation layer, the content of the structural unit from the polyamine compound is 20-50wt%, and the content of the structural unit from the polyacyl chloride is 50-80wt%. It can be determined by nuclear magnetic resonance, infrared and XPS spectrum analysis, or calculated based on the difference between the feed amount and the residual amount when preparing the separation layer.

[0057] According to the present invention, the ethanol flux of the composite nanofiltration membrane is ≥1.5Lm -2 h -1 bar -1 , hexane flux ≥ 0.3Lm - 2 h -1 bar -1 , Sudan III retention 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, mixing and dissolving a dispersion containing nano manganese dioxide with a polymer to obtain a film casting solution;

[0060] S2, loading the casting solution on a non-woven fabric and performing phase conversion to obtain a support layer substrate-I;

[0061] S3, soaking the support layer substrate-I in a tannic acid solution for a first time, and then soaking it in a ferric chloride solution for a second time to obtain a support layer substrate-II;

[0062] S4, soaking the support layer substrate-II in a polyamine solution for a third time, and then soaking it in a polyacyl chloride solution for a fourth time to obtain an initial nanofiltration membrane;

[0063] S5. Heat-treating the initial nanofiltration membrane to obtain the composite nanofiltration membrane.

[0064] In the present invention, the preparation method of the composite nanofiltration membrane is simple, and tannic acid contains a large amount of phenolic hydroxyl groups and ester structures, which can form hydrogen bonds with oxygen atoms in nano manganese dioxide in the support layer while complexing with iron ions, and interact with amine groups in the separation layer, thereby improving the overall stability of the composite nanofiltration membrane.

[0065] In the present 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 immersed in an alcohol solution of hexamethylenediamine for further cross-linking.

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

[0067] In the present invention, the dispersion containing nano manganese dioxide can be prepared according to conventional methods in the art. In the present invention, the dispersion containing nano manganese dioxide is obtained by adding nano manganese dioxide into a solvent and ultrasonically dispersing the nano manganese dioxide.

[0068] In the present invention, the ultrasonic dispersion time is 30-180 min and the temperature is 20-30°C.

[0069] In the present invention, the mixing is performed by stirring, and there is no particular limitation on the stirring conditions, as long as the polymer can be dissolved. For example, in the present 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 12-28wt%.

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

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

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

[0075] In the present invention, the mass ratio of the nano manganese dioxide to the polymer satisfies the above range, and a support layer with a specific pore structure and porosity can be obtained, 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 polyaramid.

[0078] According to the present invention, in step S2, the casting solution is scraped onto a non-woven fabric and immersed in a coagulation bath for phase inversion, wherein the solvent used in the coagulation bath is a poor solvent for the polymer.

[0079] In the present invention, the poor solvent for the polymer may be water.

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

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

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

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

[0084] In the present invention, the mass concentrations of the tannic acid and ferric chloride meet the above ranges, which can enable the tannic acid to fully complex with iron ions, strengthen the interaction between tannic acid and nano-manganese dioxide, and enhance the electrostatic interaction with the amino groups in the separation layer, thereby improving the separation performance of the composite nanofiltration membrane in the solvent as a whole.

[0085] According to the present invention, the conditions of the first soaking and the second soaking 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 includes a polyamine compound and water.

[0087] According to the present invention, in the polyamine solution, the amount of the polyamine compound is 0.1-10 g, preferably 0.2-2 g, relative to 100 mL 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 polyacid chloride solution comprises a polyacid chloride compound and a second solvent;

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

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

[0092] According to the present invention, the second solvent is not miscible with water.

[0093] In the present invention, the second solvent can dissolve the polyacyl chloride compound but is not miscible with water, so that the polyamine and the polyacyl chloride can react better at the interface between the two solvents to form a film.

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

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

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

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

[0098] In the present invention, the heat treatment satisfies the above range, which can further increase the crosslinking degree of the polyamide obtained by the reaction of the polyamine and the polyacyl chloride.

[0099] The 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 aspect of the present invention or the third aspect of the present invention in the field of separation.

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

[0102] In the following examples, the average particle size of nano manganese dioxide was measured by 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 by an ultrafiltration membrane pore size analyzer (PSMA-10, Nanjing Gaoqian Functional Materials Technology Co., Ltd.);

[0105] The thickness was observed by scanning electron microscopy;

[0106] The cross-linking reaction degree (DC) of the separation layer of the composite membrane is characterized by testing the oxygen element fine spectrum of the X-ray photoelectron spectroscopy (XPS) on the membrane surface, and is obtained by calculating the content of the O=C―N group and the O=C―O group according to Formula I. The peak area of ​​each peak is calculated by fitting the multiple peaks of the fine spectrum into individual peaks, which represents the content of the group. In Formula I, C –CON< is the peak area of ​​O=C―N, C –COO– is the peak area of ​​O=C―O.

[0107]

[0108] The content of each structural unit of the separation layer is calculated by subtracting the amount of residual monomers in the solution after the reaction from the amount of the corresponding monomers added before the reaction. The amount of residual monomers in the solution after the reaction is measured by gas chromatography.

[0109] The membrane separation performance was measured by dead-end filtration, and the specific test conditions were temperature 25°C, pressure 2MPa, and stirring rate 500rpm. The concentration of Sudan III ethanol solution was calculated by the absorbance and concentration curve at a wavelength of 505nm using a UV-visible spectrophotometer.

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

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

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

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

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

[0115] Example 1

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

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

[0118] S3. The supporting layer substrate-I is immersed in a tannic acid solution (25°C) consisting of 0.2 g of tannic acid and 100 g of water for a first time for 5 min, and then the excess water phase is removed. The supporting layer substrate-I is immersed in a ferric chloride solution (25°C) consisting of 0.6 g of ferric chloride and 100 g of water for a second time for 5 min, and finally washed with deionized water to obtain the supporting layer substrate-II.

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

[0120] S5. Heat the initial nanofiltration membrane at 70° C. for 5 min to obtain a composite nanofiltration membrane M1.

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

[0122] Example 2

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

[0124] S2. Use a scraper to scrape the casting solution onto a polypropylene nonwoven fabric, then immerse it in a deionized water coagulation bath to complete phase inversion, and then immerse it in a solution consisting of 5g hexamethylenediamine and 100g methanol for 6h to obtain a supporting layer substrate-I.

[0125] S3. The supporting layer substrate-I is immersed in a tannic acid solution (25°C) consisting of 0.2 g of tannic acid and 100 g of water for a first time for 5 min, and then the excess water phase is removed. The supporting layer substrate-I is immersed in a ferric chloride solution (25°C) consisting of 0.6 g of ferric chloride and 100 g of water for a second time for 5 min, and finally washed with deionized water to obtain the supporting layer substrate-II.

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

[0127] S5. Heat the initial nanofiltration membrane at 70° C. for 5 min to obtain a composite nanofiltration membrane M2.

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

[0129] Example 3

[0130] S1. Add 6 g of nano manganese dioxide (average particle size 70 nm) into 74 g of DMF, add 20 g of polyimide after ultrasonic dispersion at 25° C. for 50 min, heat to 70° C. and stir for 5 h to dissolve the polyimide, and obtain a casting solution.

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

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

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

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

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

[0136] Example 4

[0137] S1. Add 8 g of nano manganese dioxide to 76 g of DMF, disperse it ultrasonically at 25° C. for 60 min, then add 16 g of polyacrylonitrile (weight average molecular weight is 85,000 g / mol), heat to 60° C. and stir for 6 h to dissolve the polyacrylonitrile to obtain a casting solution.

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

[0139] S3. The supporting layer substrate-I is first immersed in a tannic acid solution (25°C) consisting of 0.05g of tannic acid and 100g of water for 10min, and then the excess water phase is removed. The supporting layer substrate-I is secondly immersed in a ferric chloride solution (25°C) consisting of 0.1g of ferric chloride and 100g of water for 10min, and finally washed with deionized water to obtain the supporting layer substrate-II.

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

[0141] S5. Heat the initial nanofiltration membrane at 70° C. for 5 min to obtain a composite nanofiltration membrane M4.

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

[0143] Example 5

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

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

[0146] S3. The supporting layer substrate-I is first immersed in a tannic acid solution (25°C) consisting of 0.5g of tannic acid and 100g of water for 2min, then the excess water phase is removed, and then immersed in a ferric chloride solution (25°C) consisting of 2g of ferric chloride and 100g of water for a second time for 2min, and finally washed with deionized water to obtain the supporting layer substrate-II.

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

[0148] S5. Heat the initial nanofiltration membrane at 70° C. for 5 min to obtain a composite nanofiltration membrane M5.

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

[0150] Example 6

[0151] The method of Example 2 was followed, except that the amount of nano manganese dioxide, DMAc and polyetherimide was 2.4 g, 88 g and 9.6 g, so that the solid content of the casting solution was 12 wt %, thereby obtaining a composite nanofiltration membrane M6.

[0152] The flux of composite nanofiltration membrane M6 for ethanol is 2.8 L m -2 h -1 bar -1 The Sudan III rejection rate was 91.5%, and the flux of n-hexane 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, DMAc and polyetherimide was 11 g, so that the solid content of the casting solution was 12 wt %, thereby obtaining a composite nanofiltration membrane M7.

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

[0156] Example 8

[0157] The method of Example 2 was followed, except that the particle size of the nano manganese dioxide was 90 nm, to obtain a composite nanofiltration membrane M8.

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

[0159] Example 9

[0160] The method of Example 2 was followed, except that the amount of tannic acid used was 0.05 g, and the amount of ferric chloride used was 0.05 g, to obtain a composite nanofiltration membrane M9.

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

[0162] Example 10

[0163] The method of Example 2 was followed, except that the amount of m-phenylenediamine used was 10 g and the amount of trimesoyl chloride used was 1 g, to obtain a composite nanofiltration membrane M10.

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

[0165] Comparative Example 1

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

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

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

[0169] S4. Heat the initial nanofiltration membrane at 70° C. for 5 min to obtain a composite nanofiltration membrane CM1.

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

[0171] Comparative Example 2

[0172] The method of Example 1 is different from that of step S3, that is, the composite nanofiltration membrane CM2 finally obtained does not contain an intermediate layer.

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

[0174] Comparative Example 3

[0175] The composite nanofiltration membrane CM3 was obtained by following the method of Example 1 except that nano manganese dioxide was not contained.

[0176] The flux of composite nanofiltration membrane CM3 for ethanol is 0.51 L m -2 h -1 bar -1 , Sudan III rejection was 85.3%, and the flux of n-hexane 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 by nano silicon dioxide to obtain a composite nanofiltration membrane CM4.

[0179] The flux of composite nanofiltration membrane CM4 for ethanol is 0.62 L m -2 h -1 bar -1 , Sudan III rejection was 88.2%, and the flux of n-hexane 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 unit 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 separation layer / nm Degree of cross-linking of 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 From polyamine structural units (wt%) From polyacyl 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] It can be seen from the above results that the flux of the organic solvent nanofiltration membrane prepared by the method of the present invention is significantly improved. On the one hand, the organic solvent nanofiltration membrane provided by the present invention introduces nano manganese dioxide in the supporting layer, and the gap between it and the polymer matrix provides an additional channel for the transmission of the solvent, thereby reducing the resistance of the solvent passing through and improving the flux. On the other hand, during the interfacial polymerization process of preparing the separation layer, the electrostatic and hydrogen bond interaction between the tannic acid and the polyamine monomers in the middle layer reduces the diffusion rate of the amine monomer to the oil phase, so the separation layer formed is thinner and the flux of the membrane is larger.

[0192] Comparing Example 1 with Example 5, it can be seen that when the mass ratio of nano manganese dioxide to polymer meets the more preferred range, the flux and interception comprehensive performance of the composite nanofiltration membrane are better. When the mass of the polymer is too large, the ethanol flux and Sudan III retention rate are significantly reduced.

[0193] Comparing Example 1 with Example 8, it can be seen that too large a particle size of nano manganese dioxide will lead to a significant decrease in n-hexane flux. Comparing Example 1 with Example 9, it can be seen that when the concentrations of tannic acid and iron salt are too low, the cross-linking degree of the separation layer will decrease, thereby affecting the comprehensive performance of the composite nanofiltration membrane.

[0194] In Comparative Example 1, since nano manganese dioxide was not added, and in Comparative Example 2, there was no tannic acid-iron ion complex layer, the ethanol flux and the n-hexane flux decreased significantly, and the retention rate of Sudan III also decreased slightly.

[0195] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A composite nanofiltration membrane, characterized in that: The composite nanofiltration membrane comprises a reinforcement layer and a support layer, an intermediate layer and a separation layer sequentially attached to the surface of the reinforcement layer; Wherein, the support layer is a polymer layer containing nano manganese dioxide; The middle layer is a tannic acid-iron ion complex layer; The separation layer is a polyamide layer.

2. The composite nanofiltration membrane according to claim 1, wherein In the support layer, the mass ratio of the nano manganese dioxide to the polymer is 1-50:100, preferably 10-30:100; Preferably, the average particle size of the nano manganese dioxide is 20-80 nm, preferably 30-60 nm; Preferably, the polymer is selected from at least one of polyimide, polyetherimide, cross-linked polyimide, cross-linked polyetherimide, polyacrylonitrile and polyaramid; Preferably, the material constituting the reinforcement layer is selected from polyolefin non-woven fabric and / or polyester non-woven fabric.

3. The composite nanofiltration membrane according to claim 1 or 2, wherein: The thickness of the support layer is 20-100 μm, preferably 30-60 μm; Preferably, the support layer has a porous structure, wherein the porosity of the support layer is 30-80%, preferably 50-70%; Preferably, the average pore size of the support layer is 10-100 nm, preferably 30-80 nm; Preferably, the thickness of the intermediate layer is 20-100 nm, preferably 30-60 nm; Preferably, the average pore size of the intermediate layer is 10-50 nm, preferably 15-30 nm; Preferably, the separation layer has a thickness of 20-150 nm, preferably 50-100 nm; Preferably, the average pore size of the separation layer is 0.15-0.5 nm, preferably 0.2-0.3 nm.

4. The composite nanofiltration membrane according to any one of claims 1 to 3, wherein: The separation layer is obtained by interfacial polymerization of a polyamine solution and a polyacyl chloride solution on the surface of a tannic acid iron ion complex intermediate layer.

5. The composite nanofiltration membrane according to claim 4, wherein The polyamine compound is selected from at least one of m-phenylenediamine, p-phenylenediamine, piperazine, polyethyleneimine and polyethylene polyamine; Preferably, the polyacyl chloride compound is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride.

6. The composite nanofiltration membrane according to any one of claims 1 to 5, wherein: The degree of crosslinking of the separation layer is ≥70%, preferably ≥80%.

7. A method for preparing a composite nanofiltration membrane, characterized in that: The following steps are involved: S1, mixing and dissolving a dispersion containing nano manganese dioxide with a polymer to obtain a casting solution; S2, loading the casting solution on a non-woven fabric and performing phase conversion to obtain a support layer substrate-I; S3, soaking the support layer substrate-I in a tannic acid solution for a first time, and then soaking it in a ferric chloride solution for a second time to obtain a support layer substrate-II; S4, soaking the support layer substrate-II in a polyamine solution for a third time, and then soaking it in a polyacyl chloride solution for a fourth time to obtain an initial nanofiltration membrane; S5. Heat-treating the initial nanofiltration membrane to obtain the composite nanofiltration membrane.

8. The preparation method according to claim 7, wherein: In step S1, the dispersion contains nano manganese dioxide and a first solvent; Preferably, 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; Preferably, the solid content of the casting solution is 12-28wt%, preferably 15-25wt%; Preferably, the mass ratio of the nano manganese dioxide to the polymer is 1-50:100, preferably 10-30:100; Preferably, the polymer is selected from at least one of polyimide, polyetherimide, cross-linked polyimide, cross-linked polyetherimide, polyacrylonitrile and polyaramid.

9. The preparation method according to claim 7 or 8, wherein: In step S2, the casting solution is scraped onto a non-woven fabric and immersed in a coagulation bath for phase inversion, wherein the solvent used in the coagulation bath is a poor solvent for the polymer; Preferably, in step S3, the mass concentration of tannic acid in the tannic acid solution is 0.05-0.5wt%, preferably 0.1-0.3wt%; Preferably, the mass concentration of the ferric chloride in the ferric chloride solution is 0.1-2%, preferably 0.5-1wt%; Preferably, the conditions of the first soaking and the second soaking each independently include: a temperature of 20-50° C. and a time of 0.5-30 min.

10. The preparation method according to any one of claims 7 to 9, wherein: In step S4, the polyamine solution includes a polyamine compound and water; Preferably, in the polyamine solution, the amount of the polyamine compound is 0.1-10 g, preferably 0.2-2 g, relative to 100 mL of water; Preferably, the polyamine compound is selected from at least one of m-phenylenediamine, p-phenylenediamine, piperazine, polyethyleneimine and polyethylene polyamine; Preferably, the polyacyl chloride solution comprises a polyacyl chloride compound and a second solvent; Preferably, in the polyacyl chloride solution, the amount of the polyacyl chloride compound is 0.01-1 g, preferably 0.05-0.5 g, relative to 100 mL of the second solvent; Preferably, the polyacyl chloride compound is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride; Preferably, the second solvent is immiscible with water, and is preferably selected from at least one of n-hexane, n-heptane or isoparaffin.

11. The preparation method according to any one of claims 7 to 10, wherein: The conditions of the third soaking and the fourth soaking independently include: a temperature of 20-50° C. and a time of 10-300 s; Preferably, the heat treatment conditions include: temperature of 40-80°C and time of 2-10 min.

12. A composite nanofiltration membrane prepared by the preparation method according to any one of claims 7 to 11.

13. Use of the composite nanofiltration membrane according to any one of claims 1 to 6 and 12 in the field of separation.

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