Composite separation membrane as well as preparation method and application thereof

Abstract

The invention relates to the field of membrane separation, and discloses a composite separation membrane as well as a preparation method and application thereof. The composite separation membrane comprises a base material layer and a separation layer, the separation layer has a cross-linked structure, the molecular weight cutoff of the composite separation membrane is 80-200 Daltons, and the pure water flux is 16-26 Lm <-2 > h <-1 > bar <-1 >. The separation layer of the composite separation membrane has high crosslinking degree, so that the composite separation membrane is relatively compact, low in molecular weight cutoff, relatively high in flux and low in operating pressure.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and in particular to a composite separation membrane and a preparation method and application thereof. Background Art

[0002] Chemical pollution in the aquatic environment is becoming increasingly serious and has become a focus of widespread concern and research. A large number of organic chemicals are called "micropollutants" due to their low concentrations. According to their sources and properties, they can be mainly divided into the following categories: drugs or personal care products, industrial compounds, pesticides, hormones, daily necessities and residues of these compounds. Long-term exposure to micropollutants may pose considerable risks to aquatic organisms and human health.

[0003] Currently, the main methods for removing micropollutants in water include chemical oxidation, activated carbon adsorption, biological methods and membrane separation technology.

[0004] CN110560010B provides a preparation method and use of a multilayer cyclodextrin-graphene oxide skeleton film adsorbent for removing PPCPs (pharmaceuticals and personal care products). The multilayer cyclodextrin-graphene oxide skeleton film is obtained by repeated coating using a coating method. The contact area between the adsorbent and the pollutants is increased, which satisfies the rapid diffusion of pollutants on the surface and inside of the adsorbent, and improves the adsorbent's efficiency in removing micropollutants.

[0005] CN102285712B discloses a method for removing micropollutants in water by oxidizing potassium permanganate catalyzed by ruthenium, comprising the following steps: adding potassium permanganate with a concentration of 0.5-5.0 mg / L and a ruthenium catalyst with a concentration of 0.5-5.0 mg / L into water containing micropollutants in a certain order, and treating the water sample for 5-40 minutes.

[0006] CN105600948A relates to a method for strengthening coagulation and adsorption of organic pollutants by biological activation and reuse of sludge in water treatment, which mainly involves biological activation of part of the sludge in the sedimentation tank, degradation and removal of organic matter adsorbed by the sludge, and activation and reuse of the sludge, which greatly reduces the load of conventional treatment and subsequent deep treatment, and does not cause secondary pollution to the environment. Although adsorption, advanced oxidation, biodegradation and the like have certain removal effects, the application conditions are relatively harsh and difficult to control. Membrane separation technology is favored because of its good separation effect, no by-product generation, and convenient operation and control.

[0007] Common membrane separation technologies include ultrafiltration, nanofiltration and reverse osmosis. Although ultrafiltration has the advantages of high flux and low operating cost, its molecular weight cutoff is high and its ability to remove pollutants is limited. Reverse osmosis can intercept smaller pollutants and some monovalent ions, but it has the disadvantages of high energy consumption and high operating cost. Nanofiltration has the characteristics of low operating pressure and low operating cost. Nanofiltration membrane relies on the Donnan effect to intercept high-valent ions and separate salts. The interception rate of neutral organic small molecules is limited, so it is usually unable to remove small organic molecule pollutants in water. Summary of the invention

[0008] The purpose of the present invention is to overcome the problem that the separation membrane in the prior art cannot simultaneously ensure high water flux and low molecular weight cut-off, and has a low interception rate for small organic molecule pollutants in water, and to provide a composite separation membrane and its preparation method and application. The separation layer of the composite separation membrane has a high degree of cross-linking, so that the surface of the composite separation membrane is dense, and has the characteristics of low molecular weight cut-off, high flux and low operating pressure.

[0009] In order to achieve the above-mentioned object, the present invention provides a composite separation membrane in a first aspect, wherein the composite separation membrane comprises a substrate layer and a separation layer;

[0010] The separation layer has a cross-linked structure, the molecular weight cut-off of the composite separation membrane is 80-200 Daltons, and the pure water flux is 16-26 Lm -2 h -1 bar -1 .

[0011] A second aspect of the present invention provides a method for preparing a composite separation membrane, wherein the method comprises the following steps:

[0012] S1, soaking the ultrafiltration base membrane in a polyamine composite solution for the first time to obtain an initial separation membrane-I;

[0013] S2, soaking the initial separation membrane-I in an organic solution containing polyacid chloride for a second time to obtain an initial separation membrane-II;

[0014] S3, heat-treating the initial separation membrane-II to obtain a composite separation membrane;

[0015] The polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine.

[0016] The third aspect of the present invention provides a composite separation membrane prepared by the preparation method described in the second aspect of the present invention.

[0017] The fourth aspect of the present invention provides an application of the composite separation membrane described in the first aspect or the third aspect of the present invention in the field of separation and purification.

[0018] Through the above technical solution, the composite separation membrane provided by the present invention and its preparation method and application obtain the following beneficial effects:

[0019] (1) The composite separation membrane is thin and the separation layer has a high degree of cross-linking, so it has a high density, low operating pressure and high flux, and is suitable for intercepting low molecular weight organic molecules in water and has a high interception rate.

[0020] (2) The composite separation membrane preparation method is simple, the conditions are mild, the production cost is low, and it is easy to promote industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 is a fitting curve diagram of the retention rate and molecular weight of Example 1 of the present invention.

[0022] Figure 2 This is a surface scanning electron microscope image of the composite separation membrane A1 prepared in Example 1 of the present invention.

[0023] Figure 3 It is the surface XPS oxygen element fine spectrum and multi-peak fitting curve of the composite separation membrane A3 prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0024] 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.

[0025] A first aspect of the present invention provides a composite separation membrane, wherein the composite separation membrane comprises a substrate layer and a separation layer;

[0026] The separation layer has a cross-linked structure, the molecular weight cut-off of the composite separation membrane is 80-200 Daltons, and the pure water flux is 16-26 Lm -2 h -1 bar -1 .

[0027] In the present invention, the composite separation membrane has a low molecular weight cut-off and a high water flux, and can have a high retention rate for small organic molecule pollutants in water while satisfying the high water flux.

[0028] Furthermore, the molecular weight cut-off of the composite separation membrane is 115-155 Daltons, and the pure water flux is 23-26 Lm - 2 h -1 bar-1 .

[0029] According to the present invention, the crosslinking degree of the separation layer is ≥60%, preferably ≥75%. The crosslinking degree can be characterized and determined by testing the oxygen element fine spectrum of the X-ray photoelectron spectroscopy (XPS) on the surface of the membrane, and indicates that the separation layer has a crosslinked structure.

[0030] According to the present invention, the porosity of the substrate layer is 40-80%, and the average pore diameter is 15-30 nm.

[0031] In the present invention, the porosity and average pore size of the substrate layer satisfy the above ranges, which can ensure that the composite separation membrane has a high flux.

[0032] Furthermore, the porosity of the substrate layer is 50-70%, and the average pore diameter is 20-25 nm.

[0033] According to the present invention, the thickness of the composite separation membrane is 100-200 μm, preferably 120-160 μm.

[0034] According to the present invention, the thickness of the separation layer is 20-150 nm, preferably 50-100 nm, and more preferably 50-70 nm.

[0035] According to the present invention, the material constituting the substrate layer is selected from at least one of polyacrylonitrile, polysulfone and polyethersulfone. That is, the substrate layer is composed of at least one of porous polyacrylonitrile, porous polysulfone and porous polyethersulfone.

[0036] According to the present invention, the material constituting the separation layer is polyamide, that is, the separation layer is composed of cross-linked polyamide.

[0037] In the present invention, the polyamide contains a cross-linked structure formed by curing and cross-linking of a polyethylene polyamine compound, a branched polyethylene imine and a polyacyl chloride. The polyacyl chloride is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride, and the polyethylene polyamine compound has a structure shown in Formula I:

[0038] Among them, n≥5.

[0039] In the cross-linked polyamide separation layer, the content of the structural unit A derived from the polyethylene polyamine compound is 15-45wt%, the content of the segment B derived from the branched polyethylene imine is 5-35wt%, and the content of the structural unit C derived from the polyacyl chloride is 50-80wt%. The content can be determined by NMR, IR, XPS and other spectral analysis, or calculated based on the difference between the feed amount and the residual amount when preparing the polyamide.

[0040] Furthermore, preferably n is 5-7.

[0041] In the present invention, the inventors found that the composite separation membrane has a high degree of cross-linking, which makes the composite separation membrane relatively dense and can effectively improve the retention capacity of small molecular organic pollutants in water, such as alachlor (molecular weight 270), atrazine (molecular weight 216), hexachlor (molecular weight 291), DDT (molecular weight 355) and other pesticides or other antibiotics and endocrine disruptors.

[0042] A second aspect of the present invention provides a method for preparing a composite separation membrane, wherein the method comprises the following steps:

[0043] S1, soaking the substrate layer in a polyamine composite solution for the first time to obtain an initial separation membrane-I;

[0044] S2, soaking the initial separation membrane-I in an organic solution containing polyacid chloride for a second time to obtain an initial separation membrane-II;

[0045] S3, heat-treating the initial separation membrane-II to obtain a composite separation membrane;

[0046] The polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine.

[0047] In the present invention, the composite separation membrane preparation method is simple, the conditions are mild, and the production cost is low. Composite separation membranes with different molecular weight cutoffs can be obtained by adjusting the content and composition of polyamines and the content and composition of polyacyl chlorides in the polyamine composite solution to adapt to small molecule organic substances with different molecular weights.

[0048] In the present invention, the heat treatment conditions are not particularly limited, and the heat treatment methods and conditions commonly used in the art can be used, such as heating at 50-80° C. for 1-10 min.

[0049] According to the present invention, 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%.

[0050] According to the present invention, 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 %.

[0051] According to the present invention, the content of the polyethylene polyamine compound meets the above range, can be coordinated with branched polyethylene imine, and the separation layer formed after reacting with polyacid chloride is thinner and has higher membrane flux.

[0052] 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%.

[0053] According to the present invention, the polyethylene polyamine compound has a structure shown in Formula I;

[0054] Among them, n≥5.

[0055] In the present invention, the polyethylene polyamine compound has a structure shown in Formula I. 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 composite separation membrane.

[0056] In the present invention, the polyethylene polyamine is selected from polyethylene polyamine commonly used in the art or a mixture thereof, as long as n≥5, such as hexaethylene heptamine, heptaethylene octamine. Preferably n is 5-7.

[0057] 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.

[0058] According to the present invention, in step S2, in the organic solution containing polyacyl chloride, the concentration of the polyacyl chloride is 0.05-2.5 wt%, preferably 0.1-1 wt%.

[0059] According to the present invention, the polyacid chloride is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride.

[0060] According to the present invention, the organic solution is selected from at least one of n-hexane, n-heptane and isoparaffin.

[0061] 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.

[0062] According to the present invention, the weight average molecular weight of the branched polyethyleneimine is 1800-70000 g / mol.

[0063] In the present invention, the weight average molecular weight of the branched polyethyleneimine satisfies the above range, which can optimize the separation layer structure and obtain a composite separation membrane with a higher flux.

[0064] Furthermore, the weight average molecular weight of the branched polyethyleneimine is 10000-25000 g / mol.

[0065] According to the present invention, the polyamine composite solution further contains 0.1-2 wt % of a catalyst and 0.03-0.2 wt % of a surfactant.

[0066] According to the present invention, the catalyst is selected from at least one of sodium bicarbonate, ammonium bicarbonate, sodium hydroxide and triethylamine.

[0067] According to the present invention, the surfactant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and dodecyltrimethylammonium chloride.

[0068] The third aspect of the present invention provides a composite separation membrane prepared by the preparation method described in the second aspect of the present invention.

[0069] The fourth aspect of the present invention provides an application of the composite separation membrane described in the first aspect or the third aspect of the present invention in the field of separation and purification.

[0070] The present invention will be described in detail below through examples.

[0071] In the following embodiments,

[0072] Porosity was determined gravimetrically;

[0073] The average pore size was measured by an ultrafiltration membrane pore size analyzer (PSMA-10, Nanjing Gaoqian Functional Materials Technology Co., Ltd.);

[0074] The thickness of the composite separation membrane is measured by a thickness gauge;

[0075] The thickness of the separation layer was obtained by observing the cross section of the membrane using a scanning electron microscope;

[0076] The performance evaluation and evaluation method of the composite separation membrane are as follows:

[0077] (1) Pure water flux: The operating temperature is 25°C and the operating pressure is 5 bar. The volume of water permeating per unit membrane area per unit time is measured in Lm -2 h -1 bar -1 .

[0078] (2) Molecular weight cut-off: 100 ppm aqueous solutions of ethylene glycol, polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 600 and polyethylene glycol 800 were prepared respectively, and the retention rates R of the composite separation membranes for these solutions were tested at an operating temperature of 25°C and an operating pressure of 80 psi and calculated according to Formula II. Where, C P is the concentration of ethylene glycol or polyethylene glycol in the permeate, C f is the concentration of ethylene glycol or polyethylene glycol in the feed solution.

[0079] R=(C P -C f ) / C P × 100%, Formula II

[0080] The concentration of ethylene glycol or polyethylene glycol in the permeate and feed solution was measured by a total organic carbon analyzer, the instrument model of which was multi N / C 3100 from Jena, Germany.

[0081] like Figure 1 As shown, the relationship between the retention rate and the solute molecular weight is plotted, and then a curve is fitted. Finally, the molecular weight corresponding to the retention rate of 90% on the fitting curve is the retention molecular weight.

[0082] The cross-linking reaction degree (DC, i.e., cross-linking degree) of the separation layer in the composite separation 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 formula 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.

[0083]

[0084] 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.

[0085] Branched polyethyleneimine (weight average molecular weight 25000 g / mol), trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride were purchased from J&K Technology Co., Ltd.;

[0086] Polyethylene polyamine: hexaethylene heptamine (n is 5) and other reagents were purchased from Beijing Inokai Technology Co., Ltd.;

[0087] Isopar E is purchased from ExxonMobil.

[0088] Example 1

[0089] S1, soaking the polyacrylonitrile ultrafiltration base membrane in a composite polyamine aqueous solution (25°C) consisting of 0.3g polyethylene polyamine, 0.2g branched polyethyleneimine (weight average molecular weight 25000g / mol) and 100g water, wherein the soaking time is 30s, then taking out the base membrane, removing the residual water on the surface, and obtaining an initial separation membrane-I;

[0090] S2, soaking the initial separation membrane-I obtained in S1 in a solution (25° C.) consisting of 0.08 g of trimesoyl chloride, 0.02 g of isophthaloyl chloride and 100 g of Isopar E solvent for 30 seconds, then taking it out and removing excess solvent on the surface to obtain an initial separation membrane-II;

[0091] S3. The initial separation membrane-II obtained in S2 is placed in an oven at 60° C. and heated for 3 min for heat treatment to obtain a composite separation membrane A1.

[0092] The pure water flux of composite separation membrane A1 is 21.5Lm -2 h -1 bar -1 The molecular weight cut-off is 120, as shown in Table 1. The surface scanning electron microscopy image of the composite separation membrane A1 is shown in Figure 2 It can be seen that the surface of the composite separation membrane is uniform and dense. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0093] Example 2

[0094] S1, soaking the polysulfone ultrafiltration base membrane in a composite polyamine aqueous solution (25°C) consisting of 0.3g polyethylene polyamine, 0.2g branched polyethyleneimine (weight average molecular weight 25000g / mol) and 100g water for 60s, then taking out the base membrane and removing the residual water on the surface to obtain an initial separation membrane-I;

[0095] S2. Immerse the initial separation membrane-I in S1 in a solution (25°C) consisting of 0.05 g of trimesoyl chloride, 0.05 g of isophthaloyl chloride and 100 g of Isopar E solvent for 30 seconds, then take it out and remove excess solvent on the surface to obtain initial separation membrane-II.

[0096] S3. The initial separation membrane-II obtained in S2 is placed in an oven at 70° C. and heated for 3 min for heat treatment to obtain a composite separation membrane A2.

[0097] The pure water flux and molecular weight cutoff of the composite separation membrane A2 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0098] Example 3

[0099] S1, soaking the polyethersulfone ultrafiltration base membrane in a composite polyamine aqueous solution (25°C) consisting of 0.3g polyethylene polyamine, 0.2g branched polyethyleneimine (weight average molecular weight 25000g / mol) and 100g water for 30s, then taking out the base membrane and removing the residual water on the surface to obtain an initial separation membrane-I;

[0100] S2, soaking the initial separation membrane-I in S1 in a solution (25°C) consisting of 0.02 g of trimesoyl chloride, 0.08 g of isophthaloyl chloride and 100 g of Isopar E solvent for 30 seconds, then taking it out and removing excess solvent on the surface to obtain an initial separation membrane-II;

[0101] S3. The initial separation membrane-II in S2 is placed in an oven at 70° C. and heated for 3 min for heat treatment to obtain a composite separation membrane A3.

[0102] Figure 3 The figure in the middle is the XPS oxygen element fine curve of the surface of the composite separation membrane A3. 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.

[0103] The pure water flux and molecular weight cutoff of the composite separation membrane A3 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0104] Example 4

[0105] S1, soaking the polyacrylonitrile ultrafiltration base membrane in a polyamine aqueous solution (25°C) consisting of 0.45g polyethylene polyamine, 0.05g branched polyethyleneimine (weight average molecular weight 25000g / mol), 0.03g sodium dodecyl sulfate and 100g water for 30s, then taking out the base membrane and removing the residual water on the surface to obtain an initial separation membrane-I;

[0106] S2. The initial separation membrane-I obtained in S1 was immersed in a solution (25° C.) consisting of 0.1 g of trimesoyl chloride and 100 g of Isopar E solvent for 30 seconds, then taken out and excess solvent on the surface was removed to obtain the initial separation membrane-II.

[0107] S3. The initial separation membrane-II obtained in S2 was placed in an oven at 60° C. and heated for 3 min for heat treatment to obtain a composite separation membrane A4.

[0108] The pure water flux and molecular weight cutoff of the composite separation membrane A4 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0109] Example 5

[0110] S1, soaking the polyacrylonitrile ultrafiltration base membrane in a polyamine aqueous solution (25°C) consisting of 0.25g polyethylene polyamine, 0.25g branched polyethyleneimine (weight average molecular weight 25000g / mol), 0.03g sodium dodecyl sulfate, 0.5g ammonium bicarbonate and 100g water for 30s, then taking out the base membrane, removing the residual water on the surface to obtain the initial separation membrane-I;

[0111] S2. The initial separation membrane-I obtained in S1 was immersed in a solution (25° C.) consisting of 0.1 g terephthaloyl chloride and 100 g Isopar E solvent for 30 seconds, then taken out and excess solvent on the surface was removed to obtain the initial separation membrane-II.

[0112] S3. The initial separation membrane-II obtained in S2 was placed in an oven at 60° C. and heated for 3 min for heat treatment to obtain a composite separation membrane A5.

[0113] The pure water flux and molecular weight cutoff of the composite separation membrane A5 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0114] Example 6

[0115] Composite separation membrane A6 was obtained by following the method of Example 5 except that ammonium bicarbonate was not contained.

[0116] The pure water flux and molecular weight cutoff of the composite separation membrane A6 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0117] Example 7

[0118] Composite separation membrane A7 was obtained by following the method of Example 4 except that sodium dodecyl sulfate was not contained.

[0119] The pure water flux and molecular weight cutoff of the composite separation membrane A7 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0120] Example 8

[0121] The method of Example 5 was followed, except that the mass of polyethylene polyamine was 0.05 g and the mass of branched polyethylene imine was 0.45 g, so that the polyethylene polyamine compound accounted for 10% of the total mass of polyethylene polyamine and branched polyethylene imine, to obtain a composite separation membrane A8.

[0122] The pure water flux and molecular weight cutoff of the composite separation membrane A8 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0123] Example 9

[0124] The method of Example 5 was followed, except that the amount of terephthaloyl chloride used was 0.05 g, so that the concentration of terephthaloyl chloride was 0.05 wt %. Composite separation membrane A9 was obtained.

[0125] The pure water flux and molecular weight cutoff of the composite separation membrane A9 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0126] Example 10

[0127] The method of Example 5 was followed, except that the weight average molecular weight of the branched polyethyleneimine was 70,000 g / mol to obtain a composite separation membrane A10.

[0128] The pure water flux and molecular weight cutoff of the composite separation membrane A10 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0129] Embodiment 11

[0130] The method of Example 5 was followed, except that the amount of sodium dodecyl sulfate used was 0.5 g, so that the concentration of sodium dodecylbenzene sulfonate was 0.5 wt %, to obtain a composite separation membrane A11.

[0131] The pure water flux and molecular weight cutoff of the composite separation membrane A11 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0132] Example 12

[0133] S1, soaking the polyacrylonitrile ultrafiltration base membrane in a polyamine aqueous solution (25°C) consisting of 0.5g polyethylene polyamine, 0.5g branched polyethyleneimine (weight average molecular weight 25000g / mol), 0.2g sodium dodecylbenzene sulfonate, 1g ammonium bicarbonate and 100g water for 30s, then taking out the base membrane, removing the residual water on the surface to obtain the initial separation membrane-I;

[0134] S2. Immerse the initial separation membrane-I obtained in S1 in a solution (25° C.) consisting of 0.25 g of isophthaloyl chloride and 100 g of n-hexane solvent for 30 seconds, then take it out and remove excess solvent on the surface to obtain initial separation membrane-II.

[0135] S3. The initial separation membrane-II obtained in S2 is placed in an oven at 65° C. and heated for 2 min for heat treatment to obtain a composite separation membrane A12.

[0136] The pure water flux and molecular weight cutoff of the composite separation membrane A12 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0137] Comparative Example 1

[0138] S1, soaking the polyacrylonitrile ultrafiltration base membrane in a solution (25° C.) consisting of 0.5 g piperazine and 100 g water for 30 seconds, then taking out the base membrane and removing the residual water on the surface to obtain an initial separation membrane-I;

[0139] S2, soaking the initial separation membrane-I in S1 in 0.08 g of trimesoyl chloride, 0.02 g of isophthaloyl chloride and 100 g of Isopar E solvent for 30 seconds, then taking it out and removing excess solvent on the surface to obtain an initial separation membrane-II;

[0140] S3. Place the initial separation membrane-II in S2 in an oven at 60° C. and heat for 3 min to obtain a composite separation membrane D1.

[0141] The pure water flux and molecular weight cutoff of the composite separation membrane D1 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0142] Comparative Example 2

[0143] The method of Example 5 was followed, except that the mass of branched polyethyleneimine was 0.5 g and polyethylene polyamine was not contained, to obtain a composite separation membrane D2.

[0144] The pure water flux and molecular weight cutoff of the composite separation membrane D2 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0145] Comparative Example 3

[0146] The method of Example 5 was followed, except that the mass of polyethylene polyamine was 0.5 g and branched polyethylene imine was not contained, to obtain a composite separation membrane D3.

[0147] The pure water flux and molecular weight cutoff of the composite separation membrane D3 are shown in Table 1. The structural parameters of each layer of the composite separation membrane are shown in Table 2, and the structural units in the separation layer of the composite separation membrane are shown in Table 3.

[0148] Table 1

[0149]

[0150]

[0151] Table 2

[0152]

[0153] Table 3

[0154]

[0155]

[0156] As can be seen from Examples 1-3, the molecular weight cut-off of the composite separation membrane prepared by the present invention decreases with the increase of diacyl chloride in polyacid chloride, so it can be designed and regulated within a certain range. Comparing Example 1 with Comparative Example 1, it can be seen that the molecular weight cut-off of the composite separation membrane prepared by using a polyamine composed of polyethylene polyamine and branched polyethyleneimine instead of the traditional aqueous phase monomer piperazine is reduced from the original 387 to 120. Therefore, the removal ability of the composite separation membrane for small molecular organic pollutants with a molecular weight of 150-350 Daltons will be effectively improved, such as pesticides such as alachlor (molecular weight 270), atrazine (molecular weight 216), hexachlor (molecular weight 291), DDT (molecular weight 355) or other antibiotics and endocrine disruptors.

[0157] Comparing Example 5 with Comparative Examples 2 and 3, it can be seen that when the aqueous phase contains the two polyamines described in the present invention, the molecular weight cutoff of the composite separation membrane prepared by the method provided by the present invention is much lower than that of the composite separation membrane prepared by the aqueous phase containing only one polyamine monomer, and the flux of the former is also higher than that of the latter. Comparing Example 5 with Comparative Example 3, it can be seen that when the aqueous phase contains a catalyst, the water flux of the composite membrane can be significantly improved by the method provided by the present invention. Comparing Example 4 with Example 6, it can be seen that the excessively high content of polyethylene polyamine compounds in the total polyamines will result in a high molecular weight cutoff of the composite membrane. Comparing Example 5 with Example 9, it can be seen that a lower concentration of polyacyl chlorides will have a greater impact on the pure water flux of the composite membrane.

[0158] 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 separation membrane, characterized in that: The composite separation membrane comprises a substrate layer and a separation layer; The separation layer has a cross-linked structure, the molecular weight cut-off of the composite separation membrane is 80-200 Daltons, and the pure water flux is 16-26 Lm -2 h -1 bar -1 .

2. The composite separation membrane according to claim 1, wherein The composite separation membrane has a molecular weight cutoff of 115-155 Daltons and a pure water flux of 23-26 Lm -2 h -1 bar -1 ; Preferably, the degree of crosslinking of the separation layer is ≥60%, preferably ≥75%; Preferably, the substrate layer has a porous structure, the porosity of the substrate layer is 40-80%, preferably 50-70%, and the average pore size is 15-30 nm, preferably 20-25 nm.

3. The composite separation membrane according to claim 1 or 2, wherein The thickness of the composite separation membrane is 100-200 μm, preferably 120-160 μm; Preferably, the separation layer has a thickness of 20-150 nm, preferably 50-100 nm, and more preferably 50-70 nm.

4. The composite separation membrane according to any one of claims 1 to 3, wherein: The material constituting the substrate layer is selected from at least one of polyacrylonitrile, polysulfone and polyethersulfone; Preferably, the material constituting the separation layer is polyamide.

5. A method for preparing a composite separation membrane, characterized in that: The method comprises the following steps: S1, soaking the ultrafiltration base membrane in a polyamine composite solution for the first time to obtain an initial separation membrane-I; S2, soaking the initial separation membrane-I in an organic solution containing polyacid chloride for a second time to obtain an initial separation membrane-II; S3, heat-treating the initial separation membrane-II to obtain a composite separation membrane; The polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine.

6. The preparation method according to claim 5, wherein: 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 %.

7. The preparation method according to claim 5 or 6, wherein: The polyethylene polyamine compound has a structure shown in Formula I: Among them, n≥5; Preferably, 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.

8. The preparation method according to claim 5 or 6, wherein: In step S2, in the organic solution containing polyacyl chloride, the concentration of the polyacyl chloride is 0.05-2.5wt%, preferably 0.1-1wt%; Preferably, the polyacyl chloride is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride; Preferably, the organic solution is selected from at least one of n-hexane, n-heptane and isoparaffin.

9. The preparation method according to claim 5 or 6, wherein: The weight average molecular weight of the branched polyethyleneimine is 1800-70000 g / mol, preferably 10000-25000 g / mol.

10. The preparation method according to claim 5 or 6, 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.

11. A composite separation membrane, characterized in that: The composite separation membrane is prepared by the preparation method described in any one of claims 5-10.

12. Use of the composite separation membrane according to any one of claims 1 to 4 or claim 11 in the field of separation and purification.

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