Mixed matrix nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of membrane separation, and discloses a mixed matrix nanofiltration membrane as well as a preparation method and application thereof. The mixed matrix nanofiltration membrane comprises an enhancement layer, and a support 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; and the separation layer is a polyamide layer. In the polymer supporting layer of the mixed matrix nanofiltration membrane, the supporting layer has a rich pore structure due to the nano manganese dioxide, so that the flux of the supporting layer is improved. The hydrophilicity of the surface of the supporting layer is improved by rich hydroxyl groups on the surface of the nano-manganese dioxide, so that the subsequently generated polyamide separation layer is thinner and smaller in permeation resistance, and meanwhile, the polyamide separation layer has better solvent resistance, so that the mixed matrix nanofiltration membrane has excellent separation performance in the field of solvent-resistant nanofiltration.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and in particular to a mixed matrix 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 method. Due to the thick cortex and large filtration resistance, the flux is low and the operating pressure is high. The mixed matrix membrane prepared by filling inorganic materials as dispersed phase in the polymer continuous phase usually has a higher flux than the nanofiltration membrane prepared by pure organic polymer due to the combination of the pore effect and interface effect of inorganic materials. It has become a research hotspot for many scholars at home and abroad.

[0003] CN105536575A discloses a solvent-resistant nanofiltration mixed matrix membrane and a preparation method thereof. The membrane is obtained by the following method: A solution and B solution are sequentially coated on the surface of a polyacrylonitrile ultrafiltration membrane after sufficient water absorption, and the solvent-resistant nanofiltration mixed matrix membrane is obtained after drying; the A solution is an aqueous solution of polydopamine nanoparticles dispersed in polyethyleneimine, and the B solution is an organic solution of trimesoyl chloride. The prepared solvent-resistant nanofiltration mixed matrix membrane exhibits suitable separation performance, has better solvent resistance than pure polymer membranes, and can be used in solvents of different polarities.

[0004] CN114288881A discloses a ZIFs mixed matrix composite nanofiltration membrane and a preparation method thereof. The method comprises the steps of: 1) preparation of a functionalized support membrane, 2) immersion in a metal salt solution, 3) surface reaction to generate a selective separation layer and ZIFs, and 4) post-treatment. The nanofiltration membrane prepared by the scheme has a highly efficient interception effect on small molecule pollutants and has a high selective permeability to inorganic salts.

[0005] CN114100372A discloses a method for preparing a nanometer particle mixed matrix nanofiltration membrane for drug separation. The method comprises the following steps: firstly, aldehyde monomers, ketone monomers and amino-rich conjugated aromatic monomer molecules are used as raw materials, and imine-type conjugated microporous nanoparticles are polymerized under mild conditions, and then the nanometer mixed matrix nanofiltration membrane is prepared by interfacial polymerization. The obtained nanometer mixed matrix nanofiltration membrane has a stable structure and good hydrophilicity and anti-pollution properties.

[0006] In summary, it can be seen that most of the existing technologies for preparing mixed matrix nanofiltration membranes are to add inorganic materials to the separation layer of the composite membrane. Since the separation layer is very thin and the inorganic material has poor compatibility with the organic polymer, the introduction of inorganic materials usually causes defects in the separation layer, thus resulting in a decrease in the interception capacity. On the other hand, the above-mentioned introduced nanoparticles such as polydopamine nanoparticles, ZIFs nanoparticles, and imine-type conjugated microporous nanoparticles also have problems such as complex preparation methods and high preparation costs.

[0007] Therefore, the current problem is that there is an urgent need to research and develop a mixed matrix organic solvent nanofiltration membrane and its preparation method with high flux, good separation performance, simple preparation process and low cost. Summary of the invention

[0008] The purpose of the present invention is to overcome the problems that inorganic materials and organic polymers in the separation membranes in the prior art have poor compatibility, are prone to defects, and thus lead to reduced interception capacity, and the preparation method is complicated and costly. A mixed matrix nanofiltration membrane and its preparation method and application are provided. In the polymer support layer of the mixed matrix nanofiltration membrane, the presence of nano manganese dioxide makes the support layer have a rich pore structure, thereby improving the flux of the support layer. On the other hand, the rich hydroxyl groups on the surface of the nano manganese dioxide improve the hydrophilicity of the surface of the support layer, making the thickness of the subsequently generated polyamide separation layer thinner and the permeation resistance smaller. At the same time, the polyamide separation layer has good solvent resistance, so that the mixed matrix nanofiltration membrane has excellent separation performance in the field of solvent-resistant nanofiltration.

[0009] In order to achieve the above object, the first aspect of the present invention provides a mixed matrix nanofiltration membrane, wherein the mixed matrix nanofiltration membrane comprises: a reinforcement layer and a support layer and a separation layer sequentially attached to the surface of the reinforcement layer;

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

[0011] The separation layer is a polyamide layer.

[0012] A second aspect of the present invention provides a method for preparing a mixed matrix nanofiltration membrane, wherein the method comprises the following steps:

[0013] S1, mixing and dissolving a dispersion containing nano manganese dioxide with a polymer to obtain a casting solution;

[0014] S2, loading the casting solution on a non-woven fabric and performing phase conversion to obtain a support layer substrate;

[0015] S3, soaking the support layer substrate in a polyamine composite solution for a first time to obtain an initial nanofiltration membrane-I;

[0016] S4, soaking the initial nanofiltration membrane-I in a solution containing a polyacyl chloride compound for a second time to obtain an initial nanofiltration membrane-II, and performing a heat treatment to obtain the mixed matrix nanofiltration membrane;

[0017] The polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine.

[0018] The third aspect of the present invention provides a mixed matrix nanofiltration membrane prepared by the preparation method described in the second aspect of the present invention.

[0019] The fourth aspect of the present invention provides an application of the mixed matrix nanofiltration membrane described in the first aspect of the present invention or the third aspect of the present invention in the field of organic solvent nanofiltration and solvent-resistant nanofiltration.

[0020] Through the above technical solution, the mixed matrix nanofiltration membrane provided by the present invention and its preparation method and application obtain the following beneficial effects:

[0021] (1) In the polymer support layer of the mixed matrix nanofiltration membrane, the presence of nano manganese dioxide makes the support layer have a rich pore structure, thereby improving the flux of the support layer. In addition, the abundant hydroxyl groups on the surface of the nano manganese dioxide improve the hydrophilicity of the surface of the support layer, making the thickness of the subsequently generated polyamide separation layer thinner and the permeation resistance smaller. At the same time, the polyamide separation layer has good solvent resistance, so that the mixed matrix nanofiltration membrane has excellent separation performance in the field of solvent-resistant nanofiltration.

[0022] (2) The addition of the nano manganese dioxide to the support layer can improve the stability of the mixed matrix nanofiltration membrane; in addition, by adjusting the content of the nano manganese dioxide to regulate the separation performance of the mixed matrix nanofiltration membrane, the performance of the mixed matrix nanofiltration membrane can be easily adjusted according to actual needs, and the application range is wide.

[0023] (3) The mixed matrix nanofiltration membrane has a simple preparation method, low operating pressure and high flux, and is suitable for separation in alcohol, ester, benzene and alkane organic solvents. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a 4 μm scanning electron microscope image of the surface of the mixed matrix nanofiltration membrane A1 prepared in Example 1.

[0025] Figure 2 This is a 200nm scanning electron microscope image of the surface of the mixed matrix nanofiltration membrane A1 prepared in Example 1.

[0026] Figure 3 This is the infrared spectrum of the mixed matrix nanofiltration membrane A1 prepared in Example 1.

[0027] Figure 4It is the surface XPS oxygen element fine spectrum and multi-peak fitting curve of the composite separation membrane A2 prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0028] 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.

[0029] A first aspect of the present invention provides a mixed matrix nanofiltration membrane, wherein the mixed matrix nanofiltration membrane comprises: a reinforcement layer, and a support layer and a separation layer sequentially attached to the surface of the reinforcement layer;

[0030] The support layer is a polymer layer containing nano manganese dioxide;

[0031] The separation layer is a polyamide layer.

[0032] In the present invention, in the polymer support layer of the mixed matrix nanofiltration membrane, the presence of nano manganese dioxide makes the support layer have a rich pore structure, thereby improving the flux of the support layer. In addition, the abundant hydroxyl groups on the surface of the nano manganese dioxide improve the hydrophilicity of the surface of the support layer, thereby making the thickness of the polyamide separation layer generated subsequently thinner and the permeation resistance smaller, and at the same time making the polyamide separation layer have better solvent resistance, further improving the flux to ethanol, so that the mixed matrix nanofiltration membrane has excellent separation performance in the field of solvent-resistant nanofiltration.

[0033] According to the present invention, in the support layer, the mass ratio of the nano manganese dioxide to the polymer is 1-50:100.

[0034] 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 the membrane separation performance.

[0035] Furthermore, the mass ratio of the nano manganese dioxide to the polymer is 10-30:100.

[0036] According to the present invention, the average particle size of the nano manganese dioxide is 20-80 nm.

[0037] In the present invention, the average particle size of the nano manganese dioxide meets the above range, and a polymer support layer with well-dispersed nano manganese dioxide can be obtained.

[0038] Furthermore, the average particle size of the nano manganese dioxide is 30-60 nm.

[0039] According to the present invention, the polymer is at least one selected from the group consisting of polyimide, polyetherimide, cross-linked polyimide, cross-linked polyetherimide, polyacrylonitrile and polyaramid.

[0040] According to the present invention, the material constituting the reinforcing layer is selected from polyolefin nonwoven fabric and / or polyester nonwoven fabric.

[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%, and the average pore size of the support layer is 10-50 nm.

[0043] In the present invention, the porosity and average pore size of the support layer satisfy the above ranges, so that the support layer has a specific pore structure, thereby improving the separation performance of the mixed matrix nanofiltration membrane.

[0044] Furthermore, the support layer has a porous structure, wherein the porosity of the support layer is 50-70%, and the average pore size of the support layer is 15-30 nm.

[0045] According to the present invention, the thickness of the separation layer is 20-150 nm.

[0046] In the present invention, the thickness of the separation layer satisfies the above range, which can make the membrane flux higher.

[0047] Furthermore, the separation layer has a thickness of 50-100 nm.

[0048] According to the present invention, the average pore size of the separation layer is 0.15-0.5 nm.

[0049] In the present invention, the porosity and average pore size of the separation layer meet the above ranges, which can ensure high flux and high retention rate, and ensure excellent separation performance.

[0050] Furthermore, the average pore size of the separation layer is 0.2-0.3 nm.

[0051] According to the present invention, the polymer forming the polyamide layer includes a structural unit A provided by polyethylene polyamine, a segment B provided by branched polyethylene imine, and a structural unit C provided by a polyacid chloride compound.

[0052] According to the present invention, based on the total weight of the polymer forming the polyamide layer, the content of the structural unit A is 15-45wt%, preferably 20-35wt%; the content of the segment B is 5-35wt%, preferably 5-20wt%; the content of the structural unit C is 50-80wt%, preferably 60-70wt%.

[0053] According to the present invention, the crosslinking degree of the polyamide layer is 40-80%.

[0054] In the present invention, the contents of carboxyl groups and amide groups in the cross-linked polymer are measured by the XPS method, and the cross-linking degree of the separation layer polymer is calculated based on the measured content.

[0055] Furthermore, the cross-linking degree of the polyamide layer is 60-80%.

[0056] According to the present invention, the polyethylene polyamine has a structure shown in Formula I;

[0057] Among them, n≥5.

[0058] According to the present invention, the polyethylene polyamine is selected from at least one of hexaethylene heptamine, heptaethylene octamine and octaethylene nonamine.

[0059] In the present invention, the polyethylene polyamine can be any one selected from hexaethylene heptamine, heptaethylene octamine, and octaethylene nonamine, or a mixture of any two or more thereof.

[0060] Furthermore, preferably n is 5-7.

[0061] According to the present invention, the weight average molecular weight of the branched polyethyleneimine is 1800-70000 g / mol.

[0062] In the present invention, the weight average molecular weight of the branched polyethyleneimine satisfies the above range, and the prepared separation layer is thinner and has a higher retention rate.

[0063] According to the present invention, the polyacyl chloride compound is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride.

[0064] According to the present invention, the toluene flux of the mixed matrix nanofiltration membrane is ≥5Lm -2 h -1 bar -1 , ethanol flux ≥ 2.5Lm - 2 h -1 bar -1 , Sudan III retention rate ≥ 90%.

[0065] According to the present invention, the inventors further found that when the support layer is further cross-linked to obtain a mixed matrix nanofiltration membrane, it can have a high flux for ethanol solvent and toluene solvent, and further have a high flux for DMF solvent. Specifically, the flux of DMF is ≥5L m -2 h -1 .

[0066] A second aspect of the present invention provides a method for preparing a mixed matrix nanofiltration membrane, wherein the method comprises the following steps:

[0067] S1, mixing and dissolving a dispersion containing nano manganese dioxide with a polymer to obtain a casting solution;

[0068] S2, loading the casting solution on a non-woven fabric and performing phase conversion to obtain a support layer substrate;

[0069] S3, soaking the support layer substrate in a polyamine composite solution for a first time to obtain an initial nanofiltration membrane-I;

[0070] S4, soaking the initial nanofiltration membrane-I in a solution containing a polyacyl chloride compound for a second time to obtain an initial nanofiltration membrane-II, and performing a heat treatment to obtain the mixed matrix nanofiltration membrane;

[0071] The polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine.

[0072] In the present invention, nano manganese dioxide and polymer are prepared to obtain a casting solution, which can increase the interfacial effect between manganese dioxide and polymer, thereby making the support layer prepared subsequently have a rich pore structure, thereby improving the separation efficiency. In addition, the support layer substrate is respectively immersed in a polyamine composite solution and a solution containing a polyacyl chloride compound for a first soak and a second soak, respectively, so that the polyamine compound and the polyacyl chloride compound are interfacially polymerized on the surface of the support layer to form a polyamide separation layer. The inventors have found that due to the presence of abundant hydroxyl groups on the surface of the nano manganese dioxide, the polyamide separation layer generated by the interfacial polymerization reaction can be made thinner and have a smaller permeation resistance, thereby further improving the separation efficiency of the mixed matrix nanofiltration membrane.

[0073] 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.

[0074] In the present invention, the solvent is not particularly limited. Considering the subsequent process, the solvent can be a solvent that can dissolve the polymer, such as N,N-dimethylformamide, N-methylpyrrolidone, N,N-dimethylacetamide, dimethyl sulfoxide, tetrahydrofuran, dioxane, acetonitrile, acetone, chloroform, etc.

[0075] In the present invention, there is no particular limitation on the conditions for ultrasonic dispersion. For example, ultrasonic dispersion can be performed at 10-60° C. and 20 kHz-200 kHz for 30-120 min.

[0076] According to the present invention, in step S1, the mass ratio of the nano manganese dioxide to the polymer is 1-50:100.

[0077] 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.

[0078] Furthermore, the mass ratio of the nano manganese dioxide to the polymer is 10-30:100.

[0079] According to the present invention, the polymer is at least one selected from the group consisting of polyimide, polyetherimide, cross-linked polyimide, cross-linked polyetherimide, polyacrylonitrile and polyaramid.

[0080] According to the present invention, in step S2, the casting solution is scraped onto the non-woven fabric and immersed in a coagulation bath for the phase inversion, wherein the solvent used in the coagulation bath is a poor solvent for the polymer.

[0081] In the present invention, the poor solvent for the polymer may be at least one of water, methanol, ethanol and isopropanol.

[0082] 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 can be immersed in an alcohol solution of hexamethylenediamine for cross-linking.

[0083] In the present invention, there is no particular limitation on the soaking conditions of the support layer substrate in the alcohol solution of hexamethylenediamine. For example, the support layer substrate may be soaked at 20-60° C. for 0.5-48 h.

[0084] According to the present invention, in step S3, in the polyamine composite solution, the total mass concentration of the polyethylene polyamine compound and the branched polyethylene imine is 0.1-5wt%, preferably 0.2-2wt%;

[0085] Preferably, based on the total weight of the polyethylene polyamine compound and the branched polyethylene imine, the content of the polyethylene polyamine compound is 10-99 wt %.

[0086] In the present invention, based on the total mass of the polyethylene polyamine compound and the branched polyethylene imine, the content of the polyethylene polyamine compound satisfies the above range, and a separation layer with a smaller pore size and a thinner thickness can be obtained.

[0087] Furthermore, based on the total weight of the polyethylene polyamine compound and the branched polyethylene imine, the content of the polyethylene polyamine compound is 50-95 wt%.

[0088] According to the present invention, the polyethylene polyamine has a structure shown in Formula II;

[0089] Among them, n≥5.

[0090] In the present invention, the types of the polyethylene polyamines are the same as those described in the first aspect of the present invention, and will not be described in detail again.

[0091] In the present invention, each polyethylene polyamine compound molecule contains two primary amines and multiple secondary amines, and polyacyl chlorides can react with primary amines and secondary amines to form a cross-linked polyamide structure. Compared with commonly used small molecules such as amine monomers such as piperazine and m-phenylenediamine, polyethylene polyamine has a suitable molecular weight and a longer chain structure, and its diffusion rate is slower, and it can better perform interfacial polymerization with polyacyl chlorides to prepare a thinner mixed matrix nanofiltration membrane.

[0092] According to the present invention, the weight average molecular weight of the branched polyethyleneimine is 1800-70000 g / mol.

[0093] According to the present invention, in step S4, in the solution containing the polyacyl chloride compound, the concentration of the polyacyl chloride compound is 0.05-2.5wt%, preferably 0.08-0.5wt%.

[0094] According to the present invention, the polyacyl chloride compound is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride.

[0095] According to the present invention, the solvent in the solution containing the polyacyl chloride compound is selected from at least one of n-hexane, n-heptane and isoparaffin.

[0096] According to the present invention, the conditions of the first immersion and the second immersion each independently include: a temperature of 20-30° C. and a time of 10-300 s.

[0097] According to the present invention, the heat treatment conditions include: temperature of 50-80° C. and time of 1-10 min.

[0098] In some embodiments of the present invention, the heat treatment can further increase the cross-linking degree of the separation layer polymer and improve the stability of the composite membrane.

[0099] According to the present invention, based on the total amount of the polyamine composite solution, the polyamine composite solution further contains 0.1-2 wt % of a catalyst and 0.03-0.2 wt % of a surfactant.

[0100] In the present invention, the inventors found that when the polyamine composite solution contains a catalyst, the flux of the mixed matrix nanofiltration membrane can be further improved. When the polyamine composite solution contains a surfactant, the retention performance of the mixed matrix nanofiltration membrane can be further improved.

[0101] According to the present invention, the catalyst is selected from at least one of sodium bicarbonate, ammonium bicarbonate, sodium hydroxide and triethylamine.

[0102] According to the present invention, the surfactant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and dodecyltrimethylammonium chloride.

[0103] The third aspect of the present invention provides a mixed matrix nanofiltration membrane prepared by the preparation method described in the second aspect of the present invention.

[0104] In the present invention, the mixed matrix nanofiltration membrane has the same structure and performance as the mixed matrix nanofiltration membrane described in the first aspect of the present invention, and will not be described in detail here.

[0105] The fourth aspect of the present invention provides an application of the mixed matrix nanofiltration membrane described in the first aspect of the present invention or the third aspect of the present invention in the field of organic solvent nanofiltration and solvent-resistant nanofiltration.

[0106] The present invention will be described in detail below through examples.

[0107] In the following examples, the average particle size of nano manganese dioxide was measured by a particle size analyzer;

[0108] The porosity of the substrate layer was determined by gravimetric method;

[0109] The average pore size of the substrate layer was measured by an ultrafiltration membrane pore size analyzer (PSMA-10, Nanjing Gaoqian Functional Materials Technology Co., Ltd.);

[0110] The thickness of the separation layer was observed by scanning electron microscopy;

[0111] 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, and the calculation is shown in Formula III. By fitting the multiple peaks of the fine spectrum into individual peaks, the peak area of ​​each peak is calculated, which represents the content of the group. In Formula III, C –CON< is the peak area of ​​O=C―N, C –COO– is the peak area of ​​O=C―O.

[0112]

[0113] 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.

[0114] 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.

[0115] Polyimide, purchased from Evonik, brand P84.

[0116] Polyetherimide was purchased from SABIC Innovative Plastics (China) Co., Ltd., with the brand name Ultem 1000.

[0117] Nano manganese dioxide was purchased from Shanghai Naio Nano Technology Co., Ltd. with an average particle size of 50 nm and 80 nm.

[0118] Nano-silicon dioxide was purchased from Shenzhen Jingcai Chemical Co., Ltd. with an average particle size of 50 nm.

[0119] Branched polyethyleneimine (weight average molecular weight 25000), trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride were purchased from J&K Technology Co., Ltd.; polyethylene polyamine (n is 5) reagent was purchased from Beijing Inokai Technology Co., Ltd.

[0120] Isopar E, purchased from ExxonMobil.

[0121] The cross-linked polyimide support layer and the cross-linked polyetherimide support layer were made in the laboratory by the following method:

[0122] The polyimide support layer and the polyetherimide support layer were immersed in a methanol solution containing 4 wt % hexamethylenediamine for 4 hours at room temperature, and then washed with deionized water for later use.

[0123] Example 1

[0124] S1, adding 2.5g of nano manganese dioxide to 37.5g of N,N-dimethylacetamide, and adding 10g of polyetherimide after ultrasonic dispersion for 60min, heating and stirring to dissolve the polymer to obtain a casting solution;

[0125] S2, scraping the casting solution onto a polypropylene non-woven fabric, immersing it in deionized water for phase conversion, and obtaining a support layer substrate;

[0126] S3, soaking the support layer substrate in a polyamine composite solution (25° C.) consisting of 0.4 g polyethylene polyamine, 0.1 g branched polyethylene imine and 100 g water for 30 seconds, removing the residual water on the surface and obtaining an initial nanofiltration membrane-I;

[0127] S4, soaking the initial nanofiltration membrane-I in 0.08 g of trimesoyl chloride, 0.02 g of isophthaloyl chloride and 100 g of Isopar E solvent (25° C.) for a second time for 30 seconds, removing and removing the Isopar E solvent remaining on the surface, to obtain an initial nanofiltration membrane-II;

[0128] S5. Heat the initial nanofiltration membrane-II in an oven at 60° C. for 3 min to obtain a mixed matrix nanofiltration membrane A1.

[0129] The mixed matrix nanofiltration membrane A1 was tested by scanning electron microscopy. Figure 1 and Figure 2 It can be found that the mixed matrix nanofiltration membrane has a uniform and dense structure on the membrane surface at 4μm and 200nm. Figure 3 The characteristic absorption peak of amide structure appeared in the infrared spectrum, indicating that polyamine and polyacyl chloride reacted to form polyamide.

[0130] Example 2

[0131] S1, adding 2.5g of nano manganese dioxide to 37.5g of N,N-dimethylacetamide, and adding 10g of polyetherimide after ultrasonic dispersion for 60min, heating and stirring to dissolve the polymer to obtain a casting solution;

[0132] S2, scraping the casting solution onto a polypropylene nonwoven fabric, immersing it in deionized water for phase inversion, and then immersing it in a 4 wt % hexamethylenediamine methanol solution for 12 h to obtain a support layer substrate;

[0133] S3, soaking the support layer substrate in a polyamine composite solution (25° C.) consisting of 0.4 g polyethylene polyamine, 0.1 g branched polyethylene imine and 100 g water for 30 seconds, removing the residual water on the surface and obtaining an initial nanofiltration membrane-I;

[0134] S4, soaking the initial nanofiltration membrane-I in 0.08 g of trimesoyl chloride, 0.02 g of isophthaloyl chloride and 100 g of Isopar E solvent (25° C.) for a second time for 30 seconds, removing and removing the Isopar E solvent remaining on the surface, to obtain an initial nanofiltration membrane-II;

[0135] S5. Heat the initial nanofiltration membrane-II in an oven at 60°C for 3 min to obtain a mixed matrix nanofiltration membrane A2.

[0136] Figure 4 This is the XPS oxygen element fine curve of the surface of the mixed matrix nanofiltration membrane A2. The O=C-N group peak and the O=C-O group peak are obtained by peak fitting. The cross-linking degree DC is calculated by formula III by comparing their peak areas.

[0137] Example 3

[0138] S1, adding 3g of nano manganese dioxide to 37g of N,N-dimethylacetamide, and adding 10g of polyetherimide after ultrasonic dispersion for 60min, heating and stirring to dissolve the polymer to obtain a casting solution;

[0139] S2, scraping the casting liquid onto the polyolefin nonwoven fabric, immersing it in deionized water for phase conversion, and then immersing it in a 4 wt % hexamethylenediamine methanol solution for 12 hours to obtain a support layer substrate;

[0140] S3, soaking the support layer substrate in a polyamine composite solution (25° C.) consisting of 0.4 g polyethylene polyamine, 0.1 g branched polyethylene imine and 100 g water for 30 seconds, removing the residual water on the surface and obtaining an initial nanofiltration membrane-I;

[0141] S4, soaking the initial nanofiltration membrane-I in 0.02 g of trimesoyl chloride, 0.08 g of isophthaloyl chloride and 100 g of Isopar E solvent (25° C.) for a second time for 30 seconds, removing and removing the Isopar E solvent remaining on the surface, to obtain an initial nanofiltration membrane-II;

[0142] S5. Heat the initial nanofiltration membrane-II in an oven at 60°C for 3 min to obtain a mixed matrix nanofiltration membrane A3.

[0143] Example 4

[0144] S1, adding 5g of nano manganese dioxide to 35g of N,N-dimethylacetamide, ultrasonically dispersing for 60min, adding 10g of polyimide, heating and stirring to dissolve the polymer, and obtaining a casting solution;

[0145] S2, scraping the casting solution onto the polyolefin non-woven fabric, immersing it in deionized water for phase conversion, and obtaining a support layer substrate;

[0146] S3, soaking the support layer substrate in a polyamine composite solution (25° C.) consisting of 0.3 g polyethylene polyamine, 0.2 g branched polyethylene imine, 0.03 g sodium dodecyl sulfate and 100 g water for 30 seconds, removing the residual water on the surface and obtaining an initial nanofiltration membrane-I;

[0147] S4, soaking the initial nanofiltration membrane-I in 0.08 g of trimesoyl chloride, 0.02 g of isophthaloyl chloride and 100 g of Isopar E solvent (25° C.) for a second time for 30 seconds, removing and removing the Isopar E solvent remaining on the surface, to obtain an initial nanofiltration membrane-II;

[0148] S5. Heat the initial nanofiltration membrane-II in an oven at 60°C for 3 min to obtain a mixed matrix nanofiltration membrane A4.

[0149] Example 5

[0150] S1, same as Example 4;

[0151] S2, same as in Example 4;

[0152] S3, soaking the support layer substrate in a polyamine composite solution (25° C.) consisting of 0.3 g polyethylene polyamine, 0.2 g branched polyethylene imine, 0.03 g sodium dodecyl sulfate, 0.5 g ammonium bicarbonate and 100 g water for 30 seconds, removing the residual water on the surface and obtaining an initial nanofiltration membrane-I;

[0153] S4, same as in Example 4;

[0154] S5. The same as Example 4, obtain mixed matrix nanofiltration membrane A5.

[0155] Example 6

[0156] S1, adding 2g of nano manganese dioxide to 38g of N,N-dimethylacetamide, ultrasonically dispersing for 60min, adding 10g of polyetherimide, heating and stirring to dissolve the polymer, and obtaining a casting solution;

[0157] S2, scraping the casting liquid onto the polyolefin nonwoven fabric, immersing it in deionized water for phase conversion, and then immersing it in a 4 wt % hexamethylenediamine methanol solution for 12 hours to obtain a support layer substrate;

[0158] S3, soaking the support layer substrate in a polyamine composite solution (25° C.) consisting of 0.3 g polyethylene polyamine, 0.2 g branched polyethylene imine, 0.03 g sodium dodecyl sulfate, 0.5 g ammonium bicarbonate and 100 g water for 30 seconds, removing the residual water on the surface and obtaining an initial nanofiltration membrane-I;

[0159] S4, soaking the initial nanofiltration membrane-I in 0.08 g of trimesoyl chloride, 0.02 g of isophthaloyl chloride and 100 g of Isopar E solvent (25° C.) for a second time for 30 seconds, removing and removing the Isopar E solvent remaining on the surface, to obtain an initial nanofiltration membrane-II;

[0160] S5. Heat the initial nanofiltration membrane-II in an oven at 60°C for 3 min to obtain a mixed matrix nanofiltration membrane A6.

[0161] Example 7

[0162] The mixed matrix nanofiltration membrane A7 was obtained by following the method of Example 6 except that the polyamine composite solution did not contain sodium dodecyl sulfate.

[0163] Example 8

[0164] The mixed matrix nanofiltration membrane A8 was obtained by following the method of Example 6 except that the polyamine composite solution did not contain ammonium bicarbonate.

[0165] Example 9

[0166] The method of Example 6 was followed, except that the average particle size of the nano manganese dioxide was 80 nm, to obtain a mixed matrix nanofiltration membrane A9.

[0167] Example 10

[0168] The method of Example 6 was followed, except that in step S3, the polyamine composite solution consisted of 0.2 g polyethylene polyamine, 0.3 g branched polyethylene imine, 0.03 g sodium dodecyl sulfate, 0.5 g ammonium bicarbonate and 100 g water to obtain a mixed matrix nanofiltration membrane A10.

[0169] Embodiment 11

[0170] The method of Example 6 was followed, except that in step S4, 0.08 g of trimesoyl chloride and 0.02 g of isophthaloyl chloride were replaced with 0.1 g of trimesoyl chloride to obtain a mixed matrix nanofiltration membrane A11.

[0171] Example 12

[0172] The method of Example 6 was followed, except that in step S3, sodium dodecyl sulfate was 0.1 g and ammonium bicarbonate was 1 g; and in step S4, trimesoyl chloride was 0.3 g and isophthaloyl chloride was replaced with 0.2 g, to obtain a mixed matrix nanofiltration membrane A12.

[0173] Example 13

[0174] The method of Example 6 was followed, except that 0.3 g of polyethylene polyamine and 0.2 g of branched polyethylene imine were replaced with 0.5 g of polyethylene polyamine to obtain a mixed matrix nanofiltration membrane A13.

[0175] Comparative Example 1

[0176] The method of Example 6 was followed, except that nano-manganese dioxide was not contained, to obtain a nanofiltration membrane D1.

[0177] Comparative Example 2

[0178] The method of Example 6 was followed, except that nano-manganese dioxide was replaced by nano-silicon dioxide to obtain a mixed matrix nanofiltration membrane D2.

[0179] Comparative Example 3

[0180] The method of Example 6 was followed, except that 0.3 g of polyethylene polyamine and 0.2 g of branched polyethylene imine were replaced with 0.5 g of piperazine to obtain a mixed matrix nanofiltration membrane D3.

[0181] Test Case

[0182] The separation performance of the mixed matrix nanofiltration membranes prepared in the examples and comparative examples was tested, and the results 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.

[0183] Table 1

[0184]

[0185] p.s.: The support layers of Examples 1, 4, and 5 were not cross-linked and therefore dissolved in DMF.

[0186] Table 2

[0187]

[0188]

[0189] Table 3

[0190] serial number Structural unit A (wt%) Segment B (wt%) Structural unit C (wt%) Example 1 23 8 69 Example 2 22 8 70 Example 3 20 7 73 Example 4 21 10 69 Example 5 19 9 72 Example 6 22 10 68 Example 7 20 9 71 Example 8 23 12 65 Example 9 25 13 62 Example 10 18 12 70 Embodiment 11 25 11 64 Example 12 16 9 75 Example 13 29 0 71 Comparative Example 1 23 10 67 Comparative Example 2 23 10 67 Comparative Example 3 / / /

[0191] It can be seen from the examples and comparative example 1 that the mixed matrix organic solvent nanofiltration membrane prepared by the present invention has a higher flux and retention rate than the organic solvent nanofiltration membrane composed of pure polymers. It can be seen from Example 6 and comparative example 3 that the polyethylene polyamine separation layer unique to the mixed matrix organic solvent nanofiltration membrane prepared by the present invention shows a higher flux and retention rate than the traditional piperazine amide separation layer. It can be seen from Examples 3, 6-7 that the method provided by the present invention can further improve the retention performance of the nanofiltration membrane when the aqueous phase contains a surfactant; and can significantly improve the water flux of the nanofiltration membrane when the aqueous phase contains a catalyst.

[0192] Examples 1 and 2 illustrate that after the support layer is immersed in the hexamethylenediamine alcohol solution, it can resist the dissolution of DMF and has excellent flux to DMF.

[0193] 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 mixed matrix nanofiltration membrane, characterized in that The mixed matrix nanofiltration membrane comprises: a reinforcement layer, and a support layer and a separation layer sequentially attached to the surface of the reinforcement layer; The support layer is a polymer layer containing nano manganese dioxide; The separation layer is a polyamide layer.

2. The mixed matrix 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 mixed matrix nanofiltration membrane according to claim 1, 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 10-50 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 mixed matrix nanofiltration membrane according to any one of claims 1 to 3, wherein The polymer forming the polyamide layer includes a structural unit A provided by polyethylene polyamine, a segment B provided by branched polyethylene imine, and a structural unit C provided by a polyacid chloride compound; Preferably, based on the total weight of the polymer forming the polyamide layer, the content of the structural unit A is 15-45wt%, preferably 20-35wt%; the content of the segment B is 5-35wt%, preferably 5-20wt%; the content of the structural unit C is 50-80wt%, preferably 60-70wt%; Preferably, the crosslinking degree of the polyamide layer is 40-80%, preferably 60-80%.

5. The mixed matrix nanofiltration membrane according to claim 4, wherein The polyethylene polyamine has a structure shown in formula I; Among them, n≥5; The polyethylene polyamine is selected from at least one of hexaethylene heptamine, heptaethylene octamine and octaethylene nonamine; Preferably, the weight average molecular weight of the branched polyethyleneimine is 1800-70000 g / mol; Preferably, the polyacyl chloride compound is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride.

6. The mixed matrix nanofiltration membrane according to any one of claims 1 to 5, wherein: The toluene flux of the mixed matrix nanofiltration membrane is ≥5Lm -2 h -1 bar -1 , ethanol flux ≥ 2.5Lm -2 h -1 bar -1 , Sudan III retention rate ≥ 90%.

7. A method for preparing a mixed matrix nanofiltration membrane, characterized in that: The method comprises the following steps: 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; S3, soaking the support layer substrate in a polyamine composite solution for a first time to obtain an initial nanofiltration membrane-I; S4, soaking the initial nanofiltration membrane-I in a solution containing a polyacyl chloride compound for a second time to obtain an initial nanofiltration membrane-II, and performing a heat treatment to obtain the mixed matrix nanofiltration membrane; The polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine.

8. The preparation method according to claim 7, wherein: In step S1, 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; Preferably, in step S2, the casting solution is scraped onto the non-woven fabric and immersed in a coagulation bath for the phase inversion, wherein the solvent used in the coagulation bath is a poor solvent for the polymer.

9. The preparation method according to claim 7 or 8, wherein: In step S3, in the polyamine composite solution, the total mass concentration of the polyethylene polyamine compound and the branched polyethylene imine is 0.1-5wt%, preferably 0.2-2wt%; Preferably, based on the total weight of the polyethylene polyamine compound and the branched polyethylene imine, the content of the polyethylene polyamine compound is 10-99 wt %, preferably 50-95 wt %.

10. The preparation method according to any one of claims 7 to 9, wherein: The polyethylene polyamine has a structure shown in formula II; Among them, n≥5; Preferably, the weight average molecular weight of the branched polyethyleneimine is 1800-70000 g / mol.

11. The preparation method according to any one of claims 7 to 10, wherein: In step S4, in the solution containing the polyacyl chloride compound, the concentration of the polyacyl chloride compound is 0.05-2.5wt%, preferably 0.08-0.5wt%; Preferably, the polyacyl chloride compound is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride; Preferably, the solvent in the solution containing the polyacyl chloride compound is at least one selected from n-hexane, n-heptane and isoparaffin.

12. The preparation method according to any one of claims 7 to 11, wherein: The conditions of the first soaking and the second soaking each independently include: a temperature of 20-30° C. and a time of 10-300 s; Preferably, the heat treatment conditions include: temperature of 50-80°C and time of 1-10 min.

13. The preparation method according to any one of claims 7 to 12, wherein: The polyamine composite solution also contains 0.1-2 wt % of a catalyst and 0.03-0.2 wt % of a surfactant; Preferably, the catalyst is selected from at least one of sodium bicarbonate, ammonium bicarbonate, sodium hydroxide and triethylamine; Preferably, the surfactant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and dodecyltrimethylammonium chloride.

14. A mixed matrix nanofiltration membrane prepared by the preparation method according to any one of claims 7 to 13.

15. Use of the mixed matrix nanofiltration membrane according to any one of claims 1 to 6 and 14 in the field of organic solvent nanofiltration and solvent-resistant nanofiltration.

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