Organic solvent nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention relates to the technical field of membrane separation, and discloses an organic solvent nanofiltration membrane as well as a preparation method and application thereof. The organic solvent nanofiltration membrane comprises a base material layer and a separation layer attached to the base material layer, a cross-linked polymer forming the separation layer comprises a structural unit A provided by polyethylene polyamine, a chain segment B provided by branched polyethyleneimine and a structural unit C provided by a polyacyl chloride compound; the base material layer is made of a material selected from one of a polyimide ultrafiltration membrane, a polyetherimide ultrafiltration membrane, a cross-linked polyimide ultrafiltration membrane and a cross-linked polyetherimide ultrafiltration membrane. The organic solvent nanofiltration membrane comprises a base material layer and a separation layer with a cross-linked structure, and has a specific pore structure, so that the organic solvent nanofiltration membrane has relatively high stability and has the advantages of high flux and high rejection rate.

Description

Technical Field

[0001] The present invention relates to the technical field of membrane separation, and in particular to an organic solvent 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 the phase inversion method. 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 the interfacial polymerization method consists 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] CN101432060A discloses a compact cortical asymmetric membrane for improving organic solvent nanofiltration and its preparation method and use. The membrane is formed by polyimide through phase inversion, and then the membrane is cross-linked by adding an amine cross-linking agent that reacts with the imide group of the polyimide to produce amide bonds. These stabilize the membrane and can maintain the nanofiltration of the solvent even in the solvent formed by it through phase inversion. The applied pressure of the membrane operation is 30bar, so the energy consumption is high. In order to reduce the operating pressure of the membrane and improve the permeation flux of the membrane, a multi-layer thin-layer composite membrane with an intermediate layer has been developed in recent years in order to further regulate the membrane structure and improve the membrane performance.

[0004] "Ultra-permeable polyamide membranes harvested by covalent organic framework nanofiber scaffolds: a two-in-one strategy" (Chemical Science, 2019, 10(39): 9077-9083) uses COF material as an intermediate layer to prepare a thin nanocomposite membrane on a polyethersulfone ultrafiltration base 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 organic solvent nanofiltration membrane, and there are problems such as high preparation cost of COF materials and complex process.

[0005] Organic solvent nanofiltration membranes with an overall asymmetric skin structure have the advantages of simple preparation methods and stable membrane performance, but their flux is low and the operating pressure is high, so the energy consumption is large. Multi-layer thin-layer composite membranes with an intermediate layer structure show high flux, but their preparation process is complex and the separation performance is easily attenuated over time.

[0006] Therefore, there is an urgent need to research and develop an organic solvent nanofiltration membrane and a preparation method thereof with high flux, good separation performance, high stability and simple preparation process. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems of low membrane flux, poor stability and high operating pressure in the prior art, and to provide an organic solvent nanofiltration membrane and a preparation method and application thereof. The organic solvent nanofiltration membrane comprises a substrate layer and a separation layer with a cross-linked structure, and has a specific pore structure, which can make the organic solvent nanofiltration membrane have high stability and have the advantages of high flux and high retention rate.

[0008] In order to achieve the above-mentioned object, the first aspect of the present invention provides an organic solvent nanofiltration membrane, wherein the organic solvent nanofiltration membrane comprises: a substrate layer and a separation layer attached to the substrate layer;

[0009] Wherein, the cross-linked polymer forming the separation layer comprises 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;

[0010] The material constituting the substrate layer is selected from one of polyimide ultrafiltration membrane, polyetherimide ultrafiltration membrane, cross-linked polyimide ultrafiltration membrane and cross-linked polyetherimide ultrafiltration membrane.

[0011] A second aspect of the present invention provides a method for preparing an organic solvent nanofiltration membrane, wherein the method comprises:

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

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

[0014] S3, heat-treating the initial nanofiltration membrane-II to obtain an organic solvent nanofiltration membrane;

[0015] Wherein, the polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine;

[0016] The ultrafiltration base membrane is selected from one of a polyimide ultrafiltration membrane, a polyetherimide ultrafiltration membrane, a cross-linked polyimide ultrafiltration membrane and a cross-linked polyetherimide ultrafiltration membrane.

[0017] The third aspect of the present invention provides an organic solvent nanofiltration membrane prepared by the preparation method described in the second aspect of the present invention;

[0018] Preferably, the organic solvent nanofiltration membrane comprises an ultrafiltration base membrane and a separation layer attached to and formed on the ultrafiltration base membrane.

[0019] The fourth aspect of the present invention provides an application of the organic solvent nanofiltration membrane provided by the first aspect or the third aspect of the present invention in the field of separation.

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

[0021] (1) The organic solvent nanofiltration membrane comprises a substrate layer and a separation layer having a cross-linked structure, and has a specific pore structure, so that the organic solvent nanofiltration membrane has high stability and has the advantages of high flux and high retention rate.

[0022] (2) The separation performance of the organic solvent nanofiltration membrane can be adjusted according to actual needs, and the control range is wide.

[0023] (3) The organic solvent nanofiltration membrane has low operating pressure and high flux, and can be applied to the separation of alcohols, esters, benzenes and alkanes organic solvents. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a 4 μm scanning electron microscope image of the organic solvent nanofiltration membrane A1 prepared in Example 1 of the present invention;

[0025] Figure 2 is a 200nm scanning electron microscope image of the organic solvent nanofiltration membrane A1 prepared in Example 1 of the present invention;

[0026] Figure 3 is the infrared spectrum of the organic solvent nanofiltration membrane A1 prepared in Example 1 of the present invention;

[0027] Figure 4 It is the surface XPS oxygen element fine spectrum and multi-peak fitting curve of the composite separation membrane A1 prepared in Example 1 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] The first aspect of the present invention provides an organic solvent nanofiltration membrane, wherein the organic solvent nanofiltration membrane comprises: a substrate layer and a separation layer attached to the substrate layer;

[0030] Wherein, the cross-linked polymer forming the separation layer comprises 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;

[0031] The material constituting the substrate layer is selected from one of polyimide ultrafiltration membrane, polyetherimide ultrafiltration membrane, cross-linked polyimide ultrafiltration membrane and cross-linked polyetherimide ultrafiltration membrane.

[0032] The material constituting the substrate layer is selected from one of polyimide ultrafiltration membrane, polyetherimide ultrafiltration membrane, cross-linked polyimide ultrafiltration membrane and cross-linked polyetherimide ultrafiltration membrane.

[0033] In the present invention, since the molecular weight of polyethylene polyamine and branched polyethylene imine is large and the diffusion rate is slow, the thickness of the separation layer formed after the reaction with the polyacyl chloride is thin and the membrane flux is high. At the same time, since there are a large number of primary amine and secondary amine cross-linking sites in the polyethylene polyamine and branched polyethylene imine molecules, the obtained separation layer has a cross-linked structure, a high degree of cross-linking, and strong solvent resistance. At the same time, the separation layer is more compact and has good separation performance.

[0034] In the present invention, the ultrafiltration base membrane can be purchased from the market or can be obtained by oneself. Exemplarily, according to a specific embodiment of the present invention, taking a polyetherimide ultrafiltration membrane as an example, the preparation method comprises: dissolving polyetherimide in N,N-dimethylacetamide to obtain a casting solution and degassing, scraping the casting solution onto a polyolefin non-woven fabric with a flat scraper, and then immediately immersing the coated membrane in deionized water for a period of time to obtain a polyetherimide ultrafiltration membrane.

[0035] According to the present invention, based on the total amount of the cross-linked polymer forming the separation 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%.

[0036] According to the present invention, the cross-linking degree of the cross-linked polymer is ≥ 70%.

[0037] In the present invention, the cross-linking degree of the cross-linked polymer is ≥70%. At this time, the cross-linking degree of the separation layer is relatively high, and it can synergize with the base film to further improve its solvent resistance.

[0038] 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.

[0039] Furthermore, the cross-linking degree of the cross-linked polymer is ≥80%, preferably ≥90%.

[0040] According to the present invention, the average pore size of the separation layer is 0.2-0.4 nm, 0.22-0.3 nm.

[0041] According to the present invention, the substrate layer has a porous structure, the porosity of the substrate layer is 20-80%, and the average pore diameter is 10-30 nm.

[0042] In the present invention, the porosity and average pore size of the substrate layer satisfy the above ranges, so that the organic solvent nanofiltration membrane can have high ethanol flux and toluene flux.

[0043] Furthermore, the substrate layer has a porous structure, the porosity of the substrate layer is 30-60%, and the average pore diameter is 15-25 nm.

[0044] According to the present invention, the thickness of the organic solvent nanofiltration membrane is 100-300 μm, preferably 130-180 μm.

[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 ensure high flux and retention rate while ensuring stable operation of the organic solvent nanofiltration membrane.

[0047] Furthermore, the thickness of the separation layer is 30-80 nm.

[0048] According to the present invention, the toluene flux of the organic solvent nanofiltration membrane is ≥2L / (m 2 ·h·bar), ethanol flux ≥1L / (m 2 ·h·bar), Sudan III retention rate ≥90%.

[0049] According to the present invention, the organic solvent nanofiltration membrane has excellent solvent resistance stability. After being immersed in an ethanol solvent for 30 days, its flux change rate ΔT is tested, and the flux change rate ΔT is ≤110%.

[0050] Further, the flux change rate is 102-108%, more preferably 102-105%.

[0051] A second aspect of the present invention provides a method for preparing an organic solvent nanofiltration membrane, wherein the method comprises:

[0052] S1, soaking the ultrafiltration base membrane in a polyamine composite solution for the first time to obtain an initial nanofiltration membrane-I;

[0053] S2, soaking the initial nanofiltration membrane-I in an organic solution containing a polyacyl chloride compound for a second time to obtain an initial nanofiltration membrane-II;

[0054] S3, heat-treating the initial nanofiltration membrane-II to obtain an organic solvent nanofiltration membrane;

[0055] Wherein, the polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine;

[0056] The ultrafiltration base membrane is selected from one of a polyimide ultrafiltration membrane, a polyetherimide ultrafiltration membrane, a cross-linked polyimide ultrafiltration membrane and a cross-linked polyetherimide ultrafiltration membrane.

[0057] In the present invention, the preparation method is simple, wherein polyethylene polyamine compounds and branched polyethylene imine are interfacially polymerized with polyacid chlorides on an ultrafiltration base membrane to form a separation layer, the separation layer is relatively thin, has a high membrane flux and a high retention rate, and is combined with a specific ultrafiltration base membrane as a substrate layer, so that the organic solvent nanofiltration membrane can have excellent solvent resistance.

[0058] 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%.

[0059] 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%.

[0060] In the present invention, 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.

[0061] 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%.

[0062] According to the present invention, the polyethylene polyamine compound has a structure shown in Formula I;

[0063]

[0064] According to one embodiment of the present invention, n≥5.

[0065] 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 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.

[0066] Furthermore, preferably n is 5-7.

[0067] According to the present invention, the polyethylene polyamine is selected from hexaethylene heptamine and / or heptaethylene octamine.

[0068] 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.

[0069] According to the present invention, in step S2, in the organic solution containing the polyacyl chloride compound, the concentration of the polyacyl chloride compound is 0.05-2.5 wt %.

[0070] In the present invention, the concentration of the polyacyl chloride compound satisfies the above range, which can more fully react with the polyethylene polyamine compound and the branched polyethylene imine to form a denser separation layer.

[0071] Furthermore, in the organic solution containing the polyacyl chloride compound, the concentration of the polyacyl chloride compound is 0.08-0.5 wt %.

[0072] According to the present invention, the polyacyl chloride compound is selected from at least one of trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride.

[0073] According to the present invention, the organic solution is selected from at least one of n-hexane, n-heptane and isoparaffin.

[0074] 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.

[0075] According to the present invention, the weight average molecular weight of the branched polyethyleneimine is 1800-70000 g / mol.

[0076] In the present invention, the weight average molecular weight of the branched polyethyleneimine satisfies the above range, which can make the prepared separation layer thinner and have a higher retention rate at the same time.

[0077] Furthermore, the weight average molecular weight of the branched polyethyleneimine is 10000-25000 g / mol.

[0078] 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.

[0079] According to the present invention, the catalyst is selected from at least one of sodium bicarbonate, ammonium bicarbonate, sodium hydroxide and triethylamine.

[0080] According to the present invention, the surfactant is selected from at least one of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate and dodecyltrimethylammonium chloride.

[0081] According to the present invention, in step S3, the heat treatment conditions include: temperature of 50-80° C. and time of 1-10 min.

[0082] In some embodiments of the present invention, the heat treatment in step S3 can increase the degree of crosslinking of the crosslinked polymer in the separation layer and improve the stability of the composite membrane. During the heat treatment, the residual acyl chloride groups react with the primary amine and secondary amine groups to form an amide structure, which can be characterized and measured by infrared, XPS, etc.

[0083] The third aspect of the present invention provides an organic solvent nanofiltration membrane prepared by the preparation method described in the second aspect of the present invention.

[0084] According to the present invention, the organic solvent nanofiltration membrane comprises an ultrafiltration base membrane and a separation layer attached to and formed on the ultrafiltration base membrane.

[0085] The fourth aspect of the present invention provides an application of the organic solvent nanofiltration membrane provided by the first aspect or the third aspect of the present invention in the field of separation.

[0086] The present invention will be described in detail below through examples.

[0087] In the following examples, the porosity of the substrate layer was determined by gravimetric method;

[0088] 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.);

[0089] The thickness of the separation layer was observed by scanning electron microscopy;

[0090] The cross-linking reaction degree (DC, i.e., cross-linking degree) of the composite membrane separation layer 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. The calculation formula is shown in Formula II. 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.

[0091]

[0092] 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.

[0093] The separation performance of the organic solvent nanofiltration membrane 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.

[0094] The stability of the composite membrane was characterized by the flux changes before and after immersion in ethanol for 30 days.

[0095] Polyetherimide ultrafiltration membrane, purchased from SABIC Innovative Plastics (China) Co., Ltd., brand Ultem 1000;

[0096] Branched polyethyleneimine (weight average molecular weight 25000 g / mol), trimesoyl chloride, isophthaloyl chloride and terephthaloyl chloride were purchased from J&K Technology Co., Ltd.;

[0097] Polyethylene polyamine (molecular weight 275) and other reagents were purchased from Beijing Inokai Technology Co., Ltd.

[0098] The polyimide ultrafiltration membrane or the polyetherimide ultrafiltration membrane is immersed in a methanol solution containing 4 wt % hexamethylenediamine for 4 hours at room temperature, and then washed with deionized water for standby use to obtain a cross-linked polyimide ultrafiltration membrane or a cross-linked polyetherimide ultrafiltration membrane.

[0099] Example 1

[0100] S1, soaking the polyetherimide ultrafiltration base membrane in a polyamine composite solution (25°C) consisting of 0.4g polyethylene polyamine, 0.1g branched polyethyleneimine and 100g water for 30s, removing the residual water on the surface, and obtaining an initial nanofiltration membrane-I;

[0101] S2, 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 30 seconds, taking it out and removing excess solvent on the surface to obtain an initial nanofiltration membrane-II;

[0102] S3, the initial nanofiltration membrane-II was heated in an oven at 60°C for 3 min for heat treatment to obtain an organic solvent nanofiltration membrane A1. The infrared test results showed that the polyamine and the polyacyl chloride generated a polyamide structure, and the XPS characterized the content of amide groups and carboxyl groups on the membrane surface, and the crosslinking degree was calculated. The crosslinking degree, thickness, porosity, average pore size of the separation layer, and thickness of the organic solvent nanofiltration membrane A1 are shown in Table 2.

[0103] Depend on Figure 1 and Figure 2 It can be seen that the organic solvent nanofiltration membrane is relatively dense in both the 4 μm scanning electron microscope image and the 200 nm scanning electron microscope image, and the separation layer surface has no defects; Figure 3The characteristic absorption peak of amide structure appeared in the infrared spectrum, indicating that polyamine and polyacyl chloride reacted to form polyamide. Figure 4 The figure in the figure is the XPS oxygen element fine curve of the surface of organic solvent nanofiltration membrane A1. The O=C-N group peak and the O=C-O group peak are obtained by peak fitting. The crosslinking degree DC is calculated by formula II by comparing their peak areas.

[0104] Example 2

[0105] The method of Example 1 is followed, except that in step S1, the ultrafiltration base membrane is replaced with cross-linked polyetherimide; and in step S2, 0.05 g of trimesoyl chloride and 0.05 g of isophthaloyl chloride are replaced to obtain an organic solvent nanofiltration membrane A2.

[0106] Example 3

[0107] The method of Example 1 is followed, except that in step S1, the ultrafiltration base membrane is replaced with cross-linked polyimide; in step S2, 0.02 g of trimesoyl chloride and 0.08 g of isophthaloyl chloride are replaced to obtain an organic solvent nanofiltration membrane A3.

[0108] Example 4

[0109] S1, soaking the polyetherimide ultrafiltration base membrane in a polyamine composite solution (25°C) consisting of 0.3g polyethylene polyamine, 0.2g branched polyethyleneimine, 0.03g sodium dodecyl sulfate and 100g water for 30s, removing the residual water on the surface, and obtaining an initial nanofiltration membrane-I;

[0110] S2, soaking the initial nanofiltration membrane-I in 0.1 g of trimesoyl chloride and 100 g of Isopar E solvent (25° C.) for 30 seconds, taking it out and removing excess solvent on the surface to obtain an initial nanofiltration membrane-II;

[0111] S3, heating the initial nanofiltration membrane-II in an oven at 60° C. for 3 min for heat treatment to obtain an organic solvent nanofiltration membrane A4.

[0112] Example 5

[0113] S1, soaking the polyetherimide ultrafiltration base membrane in a polyamine composite solution (25°C) consisting of 0.3g polyethylene polyamine, 0.2g branched polyethyleneimine, 0.03g sodium dodecyl sulfate, 0.5g ammonium bicarbonate and 100g water for 30s, removing the residual water on the surface, and obtaining an initial nanofiltration membrane-I;

[0114] S2, soaking the initial nanofiltration membrane-I in 0.1 g of trimesoyl chloride and 100 g of Isopar E solvent (25° C.) for 30 seconds, taking it out and removing excess solvent on the surface to obtain an initial nanofiltration membrane-II;

[0115] S3, heating the initial nanofiltration membrane-II in an oven at 60° C. for 3 min for heat treatment to obtain an organic solvent nanofiltration membrane A5.

[0116] Example 6

[0117] The method of Example 5 was followed, except that in step S1, the amount of polyethylene polyamine used was 0.8 g and the amount of branched polyethylene imine used was 0.2 g, to obtain an organic solvent nanofiltration membrane A6.

[0118] Example 7

[0119] The method of Example 5 was followed, except that in step S2, 0.1 g of trimesoyl chloride was replaced with 0.08 g of trimesoyl chloride and 0.02 g of isophthaloyl chloride to obtain an organic solvent nanofiltration membrane A7.

[0120] Example 8

[0121] The method of Example 5 was followed, except that the amount of polyethylene polyamine used was 3 g and the amount of branched polyethylene imine used was 2 g, to obtain an organic solvent nanofiltration membrane A8.

[0122] Example 9

[0123] The method of Example 5 was followed, except that the amount of trimesoyl chloride used was 2.5 g, to obtain an organic solvent nanofiltration membrane A9.

[0124] Example 10

[0125] The method of Example 5 was followed, except that an equal amount of branched polyethyleneimine with a weight average molecular weight of 70,000 g / mol was used to obtain an organic solvent nanofiltration membrane A10.

[0126] Embodiment 11

[0127] The method of Example 5 was followed, except that the amount of sodium dodecyl sulfate used was 0.2 g, to obtain an organic solvent nanofiltration membrane A11.

[0128] Example 12

[0129] The method of Example 5 was followed, except that the amount of ammonium bicarbonate used was 2 g, to obtain an organic solvent nanofiltration membrane A12.

[0130] Embodiment 13

[0131] The method of Example 4 was followed, except that sodium dodecyl sulfate was not contained, to obtain an organic solvent nanofiltration membrane A13.

[0132] Comparative Example 1

[0133] The method of Example 1 was followed, except that 0.4 g of polyethylene polyamine and 0.1 g of branched polyethylene imine were replaced by 0.5 g of piperazine to obtain an organic solvent nanofiltration membrane D1.

[0134] Comparative Example 2

[0135] The method of Example 5 was followed, except that the polyetherimide ultrafiltration base membrane was replaced with a polyacrylonitrile base membrane to obtain an organic solvent nanofiltration membrane D2.

[0136] Comparative Example 3

[0137] The method of Example 5 was followed, except that branched polyethyleneimine was not contained and the amount of polyethylene polyamine was adjusted to 0.5 g to obtain an organic solvent nanofiltration membrane D3.

[0138] Comparative Example 4

[0139] The method of Example 1 was followed, except that in S1, the polyetherimide ultrafiltration base membrane was first immersed in 100 g of an aqueous solution containing 0.4 g of polyethylene polyamine for 30 seconds, then taken out and immersed in 100 g of an aqueous solution containing 0.1 g of branched polyethylene imine for 30 seconds, and finally an organic solvent nanofiltration membrane D4 was obtained.

[0140] Test Case

[0141] The organic solvent nanofiltration membranes prepared in the examples and comparative examples were tested for separation performance and stability, and the results are shown in Table 1; the stability test method is: the organic solvent nanofiltration membranes of the examples and comparative examples are immersed in ethanol solvent for 30 days, and then the flux change rate is tested, and the change rate is calculated by the following formula: change rate = (ethanol flux after solvent immersion / ethanol flux before solvent immersion) × 100%.

[0142] The porosity, average pore size and thickness of each layer of the organic solvent nanofiltration membrane prepared in the examples and comparative examples were tested, and the results are shown in Table 2. The content of the cross-linked polymer and the structural unit (segment) in the separation layer of the organic solvent nanofiltration membrane is shown in Table 3.

[0143] Table 1

[0144]

[0145] Table 2

[0146]

[0147]

[0148] Table 3

[0149] serial number Structural unit A (wt%) Segment B (wt%) Structural unit C (wt%) Example 1 21 11 68 Example 2 19 9 72 Example 3 15 8 77 Example 4 28 12 60 Example 5 25 10 65 Example 6 31 8 61 Example 7 22 8 70 Example 8 37 11 52 Example 9 15 7 78 Example 10 27 13 60 Embodiment 11 26 10 64 Example 12 23 8 69 Embodiment 13 22 9 69 Comparative Example 1 - - - Comparative Example 2 30 12 58 Comparative Example 3 39 0 71 Comparative Example 4 35 30 35

[0150] From the above results, it can be seen that the retention performance of the organic solvent nanofiltration membrane prepared by using the polyamine composed of polyethylene polyamine and branched polyethylene imine described in the present invention instead of the traditional aqueous phase monomer piperazine is significantly higher than that of the latter.

[0151] By comparing Example 5 with Example 6, it can be seen that as the content of polyethylene polyamine in the total polyamine content increases, the comprehensive performance of the flux and retention rate of the organic solvent nanofiltration membrane decreases, and the stability also decreases.

[0152] The organic solvent nanofiltration membrane prepared by using the substrate layer of the present invention has better solvent resistance and stability.

[0153] The stability of the membrane is represented by the flux change rate. Generally, the greater the flux change rate, the poorer the solvent resistance of the membrane, and the membrane is swollen by the solvent. From the data of the embodiments and comparative examples in Table 1, the flux change rate in comparative examples 1-4 is as high as 120% or more, indicating that after immersion in ethanol solvent for 30 days, the membrane flux becomes larger, the membrane swells significantly in ethanol, and the separation performance decreases.

[0154] 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. An organic solvent nanofiltration membrane, characterized in that The organic solvent nanofiltration membrane comprises: a substrate layer and a separation layer attached to the substrate layer; Wherein, the cross-linked polymer forming the separation layer comprises 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; The material constituting the substrate layer is selected from one of polyimide ultrafiltration membrane, polyetherimide ultrafiltration membrane, cross-linked polyimide ultrafiltration membrane and cross-linked polyetherimide ultrafiltration membrane.

2. The organic solvent nanofiltration membrane according to claim 1, wherein Based on the total amount of the cross-linked polymer forming the separation 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 cross-linking degree of the cross-linked polymer is ≥70%, preferably ≥80%, more preferably ≥90%; Preferably, the average pore size of the separation layer is 0.2-0.4 nm, preferably 0.22-0.3 nm; Preferably, the substrate layer has a porous structure, the porosity of the substrate layer is 20-80%, preferably 30-60%, and the average pore diameter is 10-30 nm, preferably 15-25 nm.

3. The organic solvent nanofiltration membrane according to claim 1 or 2, wherein: The thickness of the organic solvent nanofiltration membrane is 100-300 μm, preferably 130-180 μm; Preferably, the separation layer has a thickness of 20-150 nm, preferably 30-80 nm.

4. The organic solvent nanofiltration membrane according to any one of claims 1 to 3, wherein: The toluene flux of the organic solvent nanofiltration membrane is ≥2L / (m 2 ·h·bar), ethanol flux ≥1L / (m 2 ·h·bar), Sudan III retention rate ≥90%.

5. A method for preparing an organic solvent nanofiltration membrane, characterized in that: The method comprises: S1, soaking the ultrafiltration base membrane in a polyamine composite solution for the first time to obtain an initial nanofiltration membrane-I; S2, soaking the initial nanofiltration membrane-I in an organic solution containing a polyacyl chloride compound for a second time to obtain an initial nanofiltration membrane-II; S3, heat-treating the initial nanofiltration membrane-II to obtain an organic solvent nanofiltration membrane; Wherein, the polyamine composite solution contains polyethylene polyamine compounds and branched polyethylene imine; The ultrafiltration base membrane is selected from one of a polyimide ultrafiltration membrane, a polyetherimide ultrafiltration membrane, a cross-linked polyimide ultrafiltration membrane and a cross-linked polyetherimide ultrafiltration membrane.

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; Preferably, n≥5; Preferably, the polyethylene polyamine is selected from hexaethylene heptamine and / or heptaethylene octamine; 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 any one of claims 5 to 7, wherein: In step S2, in the organic 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 organic solvent is selected from at least one of n-hexane, n-heptane and isoparaffin.

9. The preparation method according to any one of claims 5 to 8, 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 any one of claims 5 to 9, 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; Preferably, in step S3, the heat treatment conditions include: temperature of 50-80° C. and time of 1-10 min.

11. An organic solvent nanofiltration membrane prepared by the preparation method according to any one of claims 5 to 10; Preferably, the organic solvent nanofiltration membrane comprises an ultrafiltration base membrane and a separation layer attached to and formed on the ultrafiltration base membrane.

12. Use of the organic solvent nanofiltration membrane according to any one of claims 1 to 3 and 10 in the field of separation.

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