Acid and alkali resistant composite nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention relates to the field of membranes, and discloses an acid and alkali resistant composite nanofiltration membrane as well as a preparation method and application thereof. The composite nanofiltration membrane sequentially comprises a bottom layer, a porous support layer and a polyurea-thiourea separation layer, the polyurea-thiourea separation layer comprises a structural unit I from polyamine, a structural unit II from a polyisocyanate compound and a structural unit III from polyisothiocyanate; wherein the structural unit I is connected with the structural unit II; and the structural unit I is connected with the structural unit III. The composite nanofiltration membrane takes polyurea-thiourea as a separation layer, so that the nanofiltration membrane has high water permeability, acid permeability and alkali permeability while having excellent acid resistance and alkali resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of membranes, in particular, to an acid and alkali resistant composite nanofiltration membrane and a preparation method and application thereof. BACKGROUND

[0002] Nanofiltration is a kind of filtration technology driven by pressure to realize material separation. The nanofiltration membrane is the core of the nanofiltration separation technology, and its pore size range is about several nanometers, which can realize the separation of monovalent ions and multivalent ions, and the efficient removal of organic matters with a molecular weight in the range of 200-1000 Da. Due to the low operating pressure, small energy consumption and high separation precision of the nanofiltration membrane, it is widely used in fresh water softening, seawater softening, drinking water purification, water quality improvement, oil-water separation, wastewater treatment and recycling, as well as grading, purification and concentration of chemical products such as dyes, antibiotics, polypeptides and polysaccharides.

[0003] At present, most of the commercial nanofiltration membranes are polyamide composite membranes, which are formed by interfacial polymerization of polyamine and polyacyl chloride on a porous support layer. The polyamide composite nanofiltration membrane has the advantages of high rejection rate and large water flux. However, due to the limitation of molecular structure, the pH range that the polyamide separation layer can withstand is narrow, and it can only maintain good filtration effect in the pH range of 2-12. When the pH of the treated liquid exceeds the above range, the polyamide molecular chain will be hydrolyzed, which will cause a significant reduction in the separation performance of the nanofiltration membrane. Therefore, a large amount of waste acid water or waste alkali water generated in the fields of metallurgy, mining, printing and dyeing, textile and pharmaceutical industry cannot be treated by using commercial polyamide nanofiltration membranes.

[0004] In order to solve the problems of standard discharge and resource recycling of industrial waste acid water or waste alkali water, foreign membrane enterprises have also developed corresponding nanofiltration membrane products. Among them, the MPF series nanofiltration membrane developed by KOCH company is the most widely used. The MPF series nanofiltration membrane can operate stably in the pH range of 0-14. The acid-resistant nanofiltration membrane Duracid NF1812C developed by GE company is a three-layer composite structure, and its separation layer material is polysulfonamide, which can maintain stability in 20% hydrochloric acid, sulfuric acid and phosphoric acid conditions, and still maintain stability in 70℃, 20% concentration of sulfuric acid conditions. Israel AMS company developed acid-resistant and alkali-resistant nanofiltration membrane products. According to US9943811A1, the membrane is a porous support layer of cross-linked polyacrylonitrile, which is prepared by interfacial polymerization of polyamine and cyanuric chloride. The HYDRACoRe series membrane product developed by NITTO ELECTRIC ENARCO, LTD. has excellent acid / alkali stability, and has achieved application in sugar decolorization and printing and dyeing fields. The HYDRACoRe series membrane is also a composite membrane, and the separation layer is sulfonated polyether sulfone (《Acid and base resistant and high temperature resistant nanofiltration membrane HYDRACoRe70pHT used for recovery of waste alkali liquid in sugar industry, Membrane Science and Technology, 32, 11-15, 2006》).

[0005] Polyurea high molecular materials have good acid / alkali resistance. In 1975, Cadotte reported the preparation of reverse osmosis membranes by interfacial polymerization of polyethyleneimine and toluene diisocyanate. However, there is no report on the acid / alkali resistance of the material, and there is no report on the separation and acid / alkali resistance of the composite membrane prepared by other structure of isocyanate. CN113509893A discloses a nanofiltration membrane with a separation layer of crosslinked polyurea structure and application of the nanofiltration membrane in acid / alkali liquid treatment. The polyurea nanofiltration membrane has excellent rejection performance and stable acid / alkali stability. However, the water flux is low, the acid / alkali permeability is not high, which limits the application of the polyurea nanofiltration membrane in the field of acid / alkali liquid purification and recovery.

[0006] Therefore, it is more practical to develop an acid / alkali resistant nanofiltration membrane material with high acid permeability and high alkali permeability. SUMMARY

[0007] The purpose of the present application is to overcome the problems of low water flux, poor acid permeability and poor alkali permeability of the acid / alkali resistant nanofiltration membrane in the prior art, and to provide an acid / alkali resistant composite nanofiltration membrane, a preparation method and application thereof. The composite nanofiltration membrane uses polyurea-sulfourea as the separation layer, so that the nanofiltration membrane has excellent acid resistance and alkali resistance, as well as high water permeability, acid permeability and alkali permeability.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present application provides an acid / alkali resistant composite nanofiltration membrane, wherein the composite nanofiltration membrane comprises a bottom layer, a porous support layer and a polyurea-sulfourea separation layer in sequence.

[0009] The polyurea-sulfourea separation layer comprises structural unit I from a polyamine, structural unit II from a polyisocyanate compound and structural unit III from a polyisothiocyanate;

[0010] The structural unit I is connected to the structural unit II by The structural unit I is connected to the structural unit III by

[0011] The structural unit I is connected to the structural unit III by The structural unit I is connected to the structural unit III by

[0012] The second aspect of the present application provides a preparation method of an acid / alkali resistant composite nanofiltration membrane, wherein the preparation method comprises the following steps:

[0013] S1, preparing a porous support layer on a bottom layer;

[0014] S2, sequentially contacting the membrane layer obtained in step S1 with an aqueous phase containing a polyamine for the first contact, and with an organic phase containing a polyisocyanate and a polyisothiocyanate for the second contact, and then heat treating to obtain the acid / alkali resistant composite nanofiltration membrane.

[0015] A third aspect of the present invention provides an acid- and alkali-resistant composite nanofiltration membrane prepared by the above-described preparation method.

[0016] The fourth aspect of this invention provides an application of the above-mentioned acid and alkali resistant composite nanofiltration membrane in the field of water treatment.

[0017] Through the above technical solutions, the acid and alkali resistant composite nanofiltration membrane, its preparation method, and its application provided by the present invention achieve the following beneficial effects:

[0018] The acid-alkali resistant composite nanofiltration membrane provided by this invention uses polyurea-thiourea as the separation layer, enabling the nanofiltration membrane to possess excellent acid and alkali resistance while also exhibiting high water permeability, acid permeability, and alkali permeability. Specifically, the acid-alkali resistant composite nanofiltration membrane provided by this invention can operate stably in aqueous solutions with pH = 0-14, possessing not only high water and alkali permeability but also strong acid / alkali resistance. Moreover, its preparation method is simple, making it highly promising for industrial applications.

[0019] In the preparation method of the acid and alkali resistant composite nanofiltration membrane provided by the present invention, the different reactivity of polyamine, polyisocyanate and polyisothiocyanate is utilized so that a dense polyurea-thiourea separation layer is formed on the surface of the porous support layer during the interfacial polymerization reaction of the three. This can significantly improve the water permeability and alkali permeability while ensuring the high salt rejection rate of the nanofiltration membrane. Attached Figure Description

[0020] Figure 1 The salt rejection rate and water flux of the composite nanofiltration membrane prepared in Example 1 vary with the soaking time in a 20 wt% HCl aqueous solution.

[0021] Figure 2 The salt rejection rate and water flux of the composite nanofiltration membrane prepared in Example 1 vary with the soaking time in a 20 wt% NaOH aqueous solution. Detailed Implementation

[0022] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0023] The first aspect of the present invention provides an acid and alkali resistant composite nanofiltration membrane, wherein the composite nanofiltration membrane comprises, in sequence, a bottom layer, a porous support layer and a polyurea-thiourea separation layer;

[0024] The polyurea-thiourea separation layer comprises structural unit I from a polyamine, structural unit II from a polyisocyanate compound, and structural unit III from a polyisothiocyanate;

[0025] The structural unit I is connected with the structural unit II through ;

[0026] The structural unit I is connected with the structural unit III through .

[0027] In the present application, the acid-alkali resistant composite nanofiltration membrane takes polyurea-thiourea as the separation layer, so that the nanofiltration membrane has excellent acid resistance and alkali resistance, high water permeability, acid permeability and alkali permeability. Specifically, the acid-alkali resistant composite nanofiltration membrane provided by the present application can be stably operated in an aqueous solution with pH = 0-14, has high water permeability and alkali permeability, strong acid / alkali resistance, and a simple preparation method, and has great industrial application prospect.

[0028] According to the present application, the content of the structural unit I is 10-80 wt%, the content of the structural unit II is 5-45 wt%, and the content of the structural unit III is 15-45 wt% based on the total weight of the polyamine-urea separation layer.

[0029] In the present application, when the contents of the structural unit I, the structural unit II and the structural unit III in the polyurea-thiourea separation layer meet the above ranges, the polyurea-thiourea separation layer has a suitable cross-linking degree and a suitable average pore size, so that the acid-alkali resistant composite nanofiltration membrane containing the polyurea-thiourea separation layer has good acid-alkali resistance, excellent acid permeability and excellent alkali permeability.

[0030] In the present application, the contents of the structural unit I, the structural unit II and the structural unit III in the polyurea-thiourea separation layer are measured by XPS element content determination method.

[0031] Further, the content of the structural unit I is 30-70 wt%, the content of the structural unit II is 10-30 wt%, and the content of the structural unit III is 20-40 wt% based on the total weight of the polyurea-thiourea separation layer.

[0032] According to the present application, the polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, ethylenediamine, 1,2-propylenediamine, 1,4-butylenediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine and polyetheramine, and is preferably polyethyleneimine.

[0033] In the present application, the polyethyleneimine has a weight average molecular weight of 1000-100000 g / mol, more preferably 2000-80000 g / mol.

[0034] According to the present application, the polyisocyanate compound is at least one selected from the group consisting of m-xylylene diisocyanate, isophorone diisocyanate, 1,6-hexane diisocyanate, toluene-2,6-diisocyanate, 1,4-phenylene diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(isocyanate phenyl), 1,3-phenylene diisocyanate, 3,3'-dichloro-4,4'-diisocyanate biphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine-ethyl ester-diisocyanate, 1,4-cyclohexyl diisocyanate, and 4-chloro-6-methyl-m-phenylene diisocyanate, preferably 1,4-phenylene diisocyanate and / or toluene-2,4-diisocyanate.

[0035] According to the present application, the polyisothiocyanate is at least one selected from the group consisting of 1,4-phenylene diisothiocyanate, 1,3-phenylene diisothiocyanate, 1,2-phenylene diisothiocyanate, 2,6-toluene diisothiocyanate, 2,3-toluene diisothiocyanate, 2,4-toluene diisothiocyanate, 2,5-toluene diisothiocyanate, 3,5-toluene diisothiocyanate 1,6-hexane diisothiocyanate, 1,5-pentane diisothiocyanate, 1,4-butane diisothiocyanate, and 1,3-propane diisothiocyanate, preferably 1,4-phenylene diisothiocyanate and / or 1,4-butane diisothiocyanate.

[0036] According to the present application, the acid- and alkali-resistant composite nanofiltration membrane has an average pore size of 0.1-0.5 nm.

[0037] According to the present application, the acid- and alkali-resistant composite nanofiltration membrane has a molecular weight cut-off of 100-500 Da.

[0038] According to the present application, the acid- and alkali-resistant composite nanofiltration membrane has a contact angle of 40-80°.

[0039] In the present application, when at least one of the average pore size, the molecular weight cut-off, and the contact angle of the composite nanofiltration membrane satisfies the above range, it indicates that the separation layer of the acid- and alkali-resistant composite nanofiltration membrane has a suitable compactness and the surface of the separation layer has excellent hydrophilicity, which can further improve the salt rejection rate, the water flux, and the acid- and alkali-resistance permeability of the acid- and alkali-resistant composite nanofiltration membrane.

[0040] In a preferred embodiment of the present application, the acid- and alkali-resistant composite nanofiltration membrane has an average pore size, a molecular weight cut-off, and a contact angle that simultaneously satisfy the above range of the present application.

[0041] Further, the acid and alkali resistant composite nanofiltration membrane has an average pore size of 0.2-0.4 nm.

[0042] Further, the acid and alkali resistant composite nanofiltration membrane has a molecular weight cut-off of 200-400 Da.

[0043] Further, the acid and alkali resistant composite nanofiltration membrane has a contact angle of 40-60°.

[0044] In the present application, the bottom layer and the porous support layer are not particularly limited and can be made of various materials having certain strength and capable of being used in nanofiltration and reverse osmosis membranes.

[0045] In the present application, the bottom layer is a non-woven fabric material, preferably polyester and / or polyethylene.

[0046] In the present application, the porous support layer material can be at least one of polyether sulfone, polysulfone, poly (arylene ether), poly (benzimidazole), poly (ether ketone), poly (ether ether ketone), poly (acrylonitrile), poly (vinylidene fluoride) and poly (aryl ether ketone).

[0047] According to the present application, the thickness of the bottom layer, the porous support layer and the polyurea-thiourea separation layer is not particularly limited and can be a conventional selection in the art, but in order to make the three layers play a better synergistic role, the resulting composite nanofiltration membrane can better have excellent acid and alkali resistance, high water flux, desalination rate, high water permeability, acid permeability and alkali permeability, preferably, the thickness of the bottom layer is 30-150 μm, preferably 50-120 μm; the thickness of the porous support layer is 10-100 μm, preferably 30-60 μm; the thickness of the polyurea-thiourea separation layer is 10-500 nm, preferably 50-300 nm.

[0048] The second aspect of the present application provides a preparation method of an acid and alkali resistant composite nanofiltration membrane, wherein the preparation method comprises the following steps:

[0049] S1, preparing a porous support layer on a bottom layer;

[0050] S2, sequentially contacting the membrane layer obtained in step S1 with an aqueous phase containing a polyamine for the first contact, and with an organic phase containing a polyisocyanate and a polyisothiocyanate for the second contact, and then performing heat treatment to obtain the acid and alkali resistant composite nanofiltration membrane.

[0051] In the preparation method, the different reactivity of the polyamine, the polyisocyanate and the polyisothiocyanate is utilized, so that the three can form a dense polyurea-thiourea separation layer on the surface of the porous support layer in the process of the interfacial polymerization, the water permeability and the alkali permeability can be greatly improved under the premise of ensuring the high salt rejection rate of the nanofiltration membrane, and the acid-alkali resistant composite nanofiltration membrane prepared by the method can better exhibit excellent acid-alkali resistance, higher water flux, desalination rate, higher water permeability, acid permeability and alkali permeability.

[0052] In the application, the method for preparing the porous support layer on the base layer is not particularly limited, and the conventional method in the art can be used for preparation, preferably the phase inversion method, specifically, a polymer solution of the porous support layer material is coated on one surface of the base layer, and the porous support layer is obtained through phase inversion.

[0053] In the application, the phase inversion method can be as follows: the support layer polymer material is dissolved in a solvent to obtain a polymer solution with a concentration of 10-20 wt%, and the polymer solution is degassed at 20-40 DEG C for 10-180 min; then the polymer solution is coated on the base layer to obtain an initial film, and then the initial film is immersed in water at a temperature of 10-30 DEG C for 10-60 min to obtain the support layer polymer porous membrane through phase inversion.

[0054] The solvent can be N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc.

[0055] According to the application, the polyamine is at least one selected from the group consisting of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, ethylenediamine, 1,2-propylenediamine, 1,4-butylenediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine and polyetheramine, and the polyethyleneimine is preferred.

[0056] In the application, the weight average molecular weight of the polyethyleneimine is 1000-100000 g / mol, and more preferably 2000-80000 g / mol.

[0057] According to the present application, the polyisocyanate compound is at least one selected from the group consisting of m-xylylene diisocyanate, isophorone diisocyanate, 1,6-hexane diisocyanate, toluene-2,6-diisocyanate, 1,4-phenylene diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenylene diisocyanate, 3,3'-dichloro-4,4'-diisocyanate diphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine-ethyl ester-diisocyanate, 1,4-cyclohexyl diisocyanate, and 4-chloro-6-methyl-m-phenylene diisocyanate, preferably 1,4-phenylene diisocyanate and / or toluene-2,4-diisocyanate.

[0058] According to the present application, the polyisothiocyanate is at least one selected from the group consisting of 1,4-phenylene diisothiocyanate, 1,3-phenylene diisothiocyanate, 1,2-phenylene diisothiocyanate, 2,6-toluene diisothiocyanate, 2,3-toluene diisothiocyanate, 2,4-toluene diisothiocyanate, 2,5-toluene diisothiocyanate, 3,5-toluene diisothiocyanate, 1,6-hexane diisothiocyanate, 1,5-pentane diisothiocyanate, 1,4-butane diisothiocyanate, and 1,3-propane diisothiocyanate, preferably 1,4-phenylene diisothiocyanate and / or 1,4-butane diisothiocyanate.

[0059] According to the present application, the content of the polyamine in the aqueous phase is 0.2-10 wt%, preferably 0.5-5 wt%.

[0060] According to the present application, the content of the polyisocyanate in the organic phase is 0.005-1 wt%, preferably 0.01-0.2 wt%; the content of the polyisothiocyanate is 0.01-1 wt%, preferably 0.02-0.2 wt%.

[0061] In the present application, when the content of the polyamine in the aqueous phase, and the content of the polyisocyanate and the polyisothiocyanate in the organic phase are controlled to meet the above ranges, the prepared acid- and alkali-resistant composite nanofiltration membrane can have excellent acid- and alkali-resistant performance, high water flux, and high salt rejection rate.

[0062] In the present application, the mass ratio of the polyisocyanate, the polyisothiocyanate, and the polyamine is not particularly limited, as long as the prepared acid- and alkali-resistant composite nanofiltration membrane can have excellent acid- and alkali-resistant performance, high water flux, and high salt rejection rate, preferably the mass ratio of the polyisocyanate, the polyisothiocyanate, and the polyamine is 0.01-1:0.01-1:1, preferably 0.02-1:0.02-1:1.

[0063] In the present application, the contact time of the membrane layer obtained in step S1 with the water phase and the organic phase in step S2 is not particularly limited, as long as the obtained acid and alkali resistant composite nanofiltration membrane can have excellent acid and alkali resistance, high water flux and desalination rate.

[0064] In the present application, in step S2, the ratio of the volume of the water phase to the membrane area of the membrane layer obtained in step S1 is 0.05-0.5 mL / cm 2 , preferably 0.1-0.2 mL / cm 2 .

[0065] In the present application, in step S2, the ratio of the volume of the organic phase to the membrane area of the membrane layer obtained in step S1 is 0.02-0.2 mL / cm 2 , preferably 0.05-0.1 mL / cm 2 .

[0066] In the present application, the type of solvent of the organic phase is not particularly limited, as long as it can dissolve the polyisocyanate and the polybromomethyl compound, preferably the solvent of the organic phase is one or more of n-hexane, dodecane, n-heptane, Isopar E, Isopar G, Isopar H, Isopar L and Isopar M.

[0067] In the present application, the conditions of heat treatment are not particularly limited, as long as the monomers can be completely polymerized, and the obtained acid and alkali resistant composite nanofiltration membrane can have excellent acid and alkali resistance, high water flux and desalination rate, preferably the heat treatment temperature is 40-150℃, preferably 50-120℃; the heat treatment time is 0.5-20 minutes, preferably 1-10 minutes.

[0068] The present application also provides a composite nanofiltration membrane prepared by the preparation method provided by the present application.

[0069] The present application also provides the use of the composite nanofiltration membrane provided by the present application and prepared by the preparation method provided by the present application in the field of water treatment.

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

[0071] In the following examples and comparative examples:

[0072] (1) The water flux of the composite nanofiltration membrane is tested by the following method: the composite nanofiltration membrane is installed in a membrane cell, and after being pre-pressed at 1.0 MPa for 0.5 h, the water permeation amount of the nanofiltration membrane is measured at a pressure of 1.5 MPa and a temperature of 25°C within 1 h, and the water flux is calculated by the following formula:

[0073] J = Q / (A-t), wherein J is the water flux, Q is the water permeation amount (L), A is the effective membrane area of the composite nanofiltration membrane (m 2 ), and t is the time (h).

[0074] (2) The rejection rate of the composite nanofiltration membrane to different salts is tested by the following method: the composite nanofiltration membrane is installed in a membrane cell, and after being pre-pressed at 1.0 MPa for 0.5 h, the change in the salt concentration in the raw water solution with an initial concentration of 2000 ppm and the permeate is measured at a pressure of 1.5 MPa and a temperature of 25°C within 1 h, and the rejection rate is calculated by the following formula:

[0075] R = (C f -C p ) / C f x 100%, wherein R is the rejection rate, C f is the salt concentration in the raw water solution, and C p is the salt concentration in the permeate.

[0076] (3) The acid resistance test of the composite nanofiltration membrane: the composite nanofiltration membrane is immersed in a water solution containing 20% by mass of HCl for 30 days, and then the water flux and the salt rejection rate of the composite nanofiltration membrane are tested every 5 days.

[0077] (4) The alkali resistance test of the composite nanofiltration membrane: the composite nanofiltration membrane is immersed in a water solution containing 20% by mass of NaOH for 30 days, and then the water flux and the salt rejection rate of the composite nanofiltration membrane are tested every 5 days.

[0078] (5) The thickness of each layer of the acid-alkali-resistant composite nanofiltration membrane is determined by a screw micrometer and a scanning electron microscope.

[0079] (6) The density of the separation layer of the acid-alkali-resistant composite nanofiltration membrane is represented by the molecular weight cut-off, and the test method is as follows: the rejection rates of the nanofiltration membrane to PEG with molecular weights of 67 Da, 200 Da, 400 Da, 600 Da and 800 Da are tested, respectively, and a graph is plotted with the molecular weight of PEG as the abscissa and the corresponding rejection rate as the ordinate, and the molecular weight cut-off of the nanofiltration membrane is defined as the molecular weight corresponding to a rejection rate of 90%, which reflects the density of the separation layer of the nanofiltration membrane.

[0080] (7) The content of each structural unit in the separation layer of the composite nanofiltration membrane is measured by X-ray photoelectron spectroscopy of the membrane sample. Specifically, after sample preparation, the full spectrum and nitrogen element fine spectrum of the sample are tested, the nitrogen element fine spectrum is peak-separated to obtain different chemical states of nitrogen element in the structure and the proportion in the structure, and the content of each structural unit of the membrane can be correspondingly converted.

[0081] (8) The average pore size of the composite nanofiltration membrane is measured by the PEG solute transfer method, and the detailed steps are as follows:

[0082] (1) Test the rejection rate of the separation membrane to PEG of different molecular sizes.

[0083] (2) Linearly fit the PEG size and the rejection rate in the log-probability coordinate system, and the PEG size corresponding to the 50% rejection rate is the average pore size of the separation membrane.

[0084] (9) The surface contact angle of the composite membrane sample is tested by static drop method using a DSA100 surface contact angle measuring instrument produced by KRUSS Company in Germany. Before testing, the sample is dried in a 60°C vacuum oven for 30 min to remove the moisture on the surface and inside, and then the dried membrane is attached to a flat glass slide with double-sided tape. The volume of each water droplet is 2μL during testing. The water droplet is dropped on the membrane surface for 3s before testing. The final contact angle is determined by taking the average value of multiple measurements.

[0085] In addition, in the following examples and comparative examples:

[0086] The branched polyethyleneimine (weight average molecular weight of 25000g / mol), 1,4-phenylene diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylene bis(isocyanate phenyl), 1,4-phenylene diisothiocyanate, 1,4-butane diisothiocyanate and 1,6-hexane diisothiocyanate, etc. are purchased from Alfa Aesar. Other chemical reagents are purchased from National Pharmaceutical Group Chemical Reagent Co., Ltd.

[0087] The support layer is prepared by phase inversion method, and the specific steps are as follows:

[0088] A certain amount of polysulfone (number average molecular weight of 80000g / mol) is dissolved in N,N-dimethylformamide to prepare a polysulfone solution with a concentration of 18wt% and is degassed at 25°C for 120min. Then, the polysulfone solution is coated on a polyethylene non-woven fabric (thickness of 75μm) using a doctor blade to obtain an initial film, which is then immersed in water at a temperature of 25°C for 60min to convert the polysulfone layer on the surface of the polyethylene non-woven fabric into a porous membrane by phase inversion. Finally, the support layer with a total thickness of 115μm is obtained after 3 times of water washing.

[0089] Example 1

[0090] The above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 1% polyethyleneimine by weight at 25°C for 60 s, and then drained. Next, the upper surface of the support layer was contacted with 40 mL of an Isopar E solution containing 0.04% 4,4'-methylenebis(phenyl isocyanate) and 0.16% 1,4-butane diisothiocyanate by weight at 25°C for 60 s, and then drained. The membrane was then placed in an oven and heated at 70°C for 3 min to obtain the composite membrane N1. The mass ratio of 4,4'-methylenebis(phenyl isocyanate), 1,4-butane diisothiocyanate, and polyethyleneimine was 0.032:0.128:1.

[0091] The obtained composite membrane N1 was soaked in water for 24 hours, and then the water flux and salt rejection rate for different salts were measured under the conditions of 1.5 MPa and 25℃. The results are shown in Table 1. The membrane sheets were soaked in aqueous solutions of 20% HCl and 20% NaOH for 30 days, respectively. The changes in water flux and salt rejection rate of the composite nanofiltration membrane were then measured every 5 days. The results are shown in Table 1. Figures 1-2 As shown.

[0092] Example 2

[0093] The above area is 400cm² 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 3% (w / w) polyethyleneimine at 25°C for 60 s, and then drained. Next, the upper surface of the support layer was contacted with 40 mL of an Isopar E solution containing 0.08% (w / w) 4,4'-methylenebis(phenyl isocyanate) and 0.32% (w / w) 1,4-butane diisothiocyanate, and drained after 60 s at 25°C. The membrane was then placed in an oven and heated at 70°C for 3 min to obtain the composite membrane N2. The mass ratio of 4,4'-methylenebis(phenyl isocyanate), 1,4-butane diisothiocyanate, and polyethyleneimine was 0.021:0.085:1.

[0094] Example 3

[0095] The above area is 400cm² 2The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 0.5% by weight of polyethyleneimine, and after 60 s of contact at 25°C, the liquid was drained; then, the upper surface of the support layer was contacted again with 40 mL of a solution of Isopar E containing 0.01% by weight of 4,4'-methylenebis(phenyl isocyanate) and 0.04% by weight of 1,4-butane diisothiocyanate, and after 60 s of contact at 25°C, the liquid was drained; then, the membrane was placed in an oven and heated at 70°C for 3 min, obtaining the composite membrane N3. The mass ratio of 4,4'-methylenebis(phenyl isocyanate), 1,4-butane diisothiocyanate and polyethyleneimine was 0.016:0.064:1.

[0096] Example 4

[0097] The composite nanofiltration membrane was prepared according to the method of Example 1, except that an equal mass of 1,4-phenylene diisothiocyanate was used instead of 4,4'-methylenebis(phenyl isocyanate), obtaining the composite membrane N4.

[0098] Example 5

[0099] The composite nanofiltration membrane was prepared according to the method of Example 1, except that an equal mass of toluene-2,4-diisocyanate was used instead of 4,4'-methylenebis(phenyl isocyanate), obtaining the composite membrane N5.

[0100] Example 6

[0101] The composite nanofiltration membrane was prepared according to the method of Example 1, except that an equal mass of 1,4-phenylene diisothiocyanate was used instead of 1,4-butane diisothiocyanate, obtaining the composite membrane N6.

[0102] Example 7

[0103] The composite nanofiltration membrane was prepared according to the method of Example 1, except that an equal mass of 1,6-hexane diisothiocyanate was used instead of 1,4-butane diisothiocyanate, obtaining the composite membrane N7.

[0104] Example 8

[0105] The composite nanofiltration membrane was prepared according to the method of Example 1, except that the concentrations of 4,4'-methylenebis(phenyl isocyanate) and 1,4-butane diisothiocyanate were 0.08% and 0.12% by mass, respectively, obtaining the composite membrane N8. The mass ratio of 4,4'-methylenebis(phenyl isocyanate), 1,4-butane diisothiocyanate and polyethyleneimine was 0.064:0.096:1.

[0106] Example 9

[0107] A composite nanofiltration membrane was prepared according to the method of Example 1, except that the concentrations of 4,4'-methylenebis(phenyl isocyanate) and 1,4-butane diisothiocyanate were 0.12 mass% and 0.08 mass%, respectively, to obtain composite membrane N9. Here, the mass ratio of 4,4'-methylenebis(phenyl isocyanate), 1,4-butane diisothiocyanate, and polyethyleneimine was 0.096:0.064:1.

[0108] Example 10

[0109] A composite nanofiltration membrane was prepared according to the method of Example 1, except that the concentrations of 4,4'-methylenebis(phenyl isocyanate) and 1,4-butane diisothiocyanate were 0.16 mass% and 0.04 mass%, respectively, to obtain composite membrane N10. Here, the mass ratio of 4,4'-methylenebis(phenyl isocyanate), 1,4-butane diisothiocyanate, and polyethyleneimine was 0.128:0.032:1.

[0110] Example 11

[0111] A composite nanofiltration membrane was prepared according to the method of Example 1, except that the concentration of 4-butane diisothiocyanate was 0.1 mass%, to obtain composite membrane N11. Here, the mass ratio of 4,4'-methylenebis(phenyl isocyanate), 1,4-butane diisothiocyanate, and polyethyleneimine was 0.032:0.08:1.

[0112] Example 12

[0113] A composite nanofiltration membrane was prepared according to the method of Example 1, except that the concentration of 4-butane diisothiocyanate was 0.2 mass%, to obtain composite membrane N11. Here, the mass ratio of 4,4'-methylenebis(phenyl isocyanate), 1,4-butane diisothiocyanate, and polyethyleneimine was 0.032:0.16:1.

[0114] Comparative Example 1

[0115] The above polyethersulfone support layer having an area of 400 cm 2 The upper surface of the polyethersulfone support layer was contacted with 50 mL of an aqueous solution containing 1% by weight of polyethyleneimine, and the liquid was drained after 60 s of contact at 25°C; then, the upper surface of the support layer was contacted with 40 mL of a solution of 4,4'-methylenebis(phenyl isocyanate) in Isopar E containing 0.2% by weight of 4,4'-methylenebis(phenyl isocyanate), and the liquid was drained after 60 s of contact at 25°C; then, the membrane was placed in an oven and heated at 70°C for 3 min to obtain composite membrane D1. Here, the mass ratio of 4,4'-methylenebis(phenyl isocyanate) and polyethyleneimine was 0.16:1.

[0116] Comparative Example 2

[0117] The above 400 cm2 2 The upper surface of the polysulfone support layer was contacted with 50 mL of an aqueous solution containing 1 wt% polyethyleneimine, and the liquid was drained after 60 s of contact at 25°C; then, the upper surface of the support layer was contacted with 40 mL of a solution of 1,4-butanediisothiocyanate in Isopar E containing 0.2 wt%, and the liquid was drained after 60 s of contact at 25°C; then, the membrane was placed in an oven and heated at 70°C for 3 min to obtain composite membrane D2. The mass ratio of 1,4-butanediisothiocyanate to polyethyleneimine was 0.16:1.

[0118] The thickness of each layer of the composite nanofiltration membrane, the molecular weight cut-off of the composite nanofiltration membrane, the average pore size, the contact angle, and the content of each structural unit in the polyamine-urea separation layer in the examples and comparative examples are shown in Table 1.

[0119] Table 1

[0120]

[0121]

[0122] Table 1 continued

[0123] Structural unit I / wt.-% Structural unit II / wt.-% Structural unit III / wt.-% Example 1 52.0 15.6 32.4 Example 2 56.8 17.4 25.8 Example 3 49.8 12.4 37.8 Example 4 52.6 18.9 28.5 Example 5 49.7 14.7 35.6 Example 6 48.9 13.8 37.3 Example 7 51.3 17.8 30.9 Example 8 50.9 20.4 28.7 Example 9 50.3 23.5 26.2 Example 10 51.0 26.9 22.1 Example 11 53.3 19.2 27.5 Example 12 48.3 15.2 36.5 Comparative Example 1 56.9 43.1 0 Comparative Example 2 59.2 0 40.8

[0124] The water flux, the rejection rate of sodium chloride, the rejection rate of sodium sulfate, the rejection rate of magnesium sulfate, the rejection rate of sodium hydroxide, the acid resistance, and the alkali resistance of the composite membranes of the examples and comparative examples were tested, and the results are shown in Table 2 and Table 3, respectively.

[0125] Table 2

[0126]

[0127]

[0128] As can be seen from Table 2, compared with the pure polyurea structure, the introduction of the thiourea structure not only improves the rejection rate of the membrane to salt ions, but also effectively improves the water flux of the membrane. On the other hand, the rejection rate of the polyurea-thiourea nanofiltration membrane to sodium hydroxide is reduced, indicating that the thiourea group has better affinity for water and alkali, which is conducive to the permeation of water molecules and hydroxide ions, and the dense crosslinked network structure effectively hinders the permeation of salt ions.

[0129] Table 3

[0130]

[0131] As can be seen from Table 3, the acid and alkali stability of the polyurea-thiourea nanofiltration membrane is more excellent than that of the pure polyurea nanofiltration membrane and the pure polythiourea nanofiltration membrane, indicating that the acid and alkali resistance of the urea-thiourea structure is better.

[0132] By Figures 1-2 It can be seen that the composite membrane with polyurea-thiourea as separation layer has excellent stability in 20 mass% HCl and 20 mass% NaOH aqueous solutions. The rejection rate of MgSO4 remains above 90%-95% after 30 days of immersion in the above extreme acidic or basic solutions. The water flux increases significantly with the increase of immersion time, indicating that the polyurea-thiourea crosslinked structure swells in the extreme acidic or basic solution.

[0133] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and belong to the protection scope of the present application.

Claims

1. An acid- and alkali-resistant composite nanofiltration membrane, characterized in that, The composite nanofiltration membrane comprises, in sequence, a bottom layer, a porous support layer, and a polyurea-thiourea separation layer; The polyurea-thiourea separation layer includes structural unit I from polyamines, structural unit II from polyisocyanate compounds, and structural unit III from polyisothiocyanates; Wherein, structural unit I and structural unit II are connected by connect; The structural unit I and the structural unit III are connected by... connect.

2. The acid- and alkali-resistant composite nanofiltration membrane according to claim 1, wherein, Based on the total weight of the polyurea-thiourea separation layer, the content of structural unit I is 10-80 wt%, the content of structural unit II is 5-45 wt%, and the content of structural unit III is 15-45 wt%. Preferably, based on the total weight of the polyurea-thiourea separation layer, the content of structural unit I is 30-70 wt%, the content of structural unit II is 10-30 wt%, and the content of structural unit III is 20-40 wt%.

3. The acid- and alkali-resistant composite nanofiltration membrane according to claim 1 or 2, wherein, The polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, ethylenediamine, 1,2-propanediamine, 1,4-butanediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, and polyetheramine. Preferably, the polyisocyanate compound is selected from at least one of the following: isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenyl diisocyanate, 3,3'-dichloro-4,4'-diisocyanate biphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine-ethyl ester-diisocyanate, 1,4-cyclohexyl diisocyanate, and 4-chloro-6-methyl isophthalic diisocyanate. Preferably, the polyisothiocyanate is at least one selected from 1,4-phenylene diisothiocyanate, 1,3-phenylene diisothiocyanate, 1,2-phenylene diisothiocyanate, 2,6-toluene diisothiocyanate, 2,3-toluene diisothiocyanate, 2,4-toluene diisothiocyanate, 2,5-toluene diisothiocyanate, 3,5-toluene diisothiocyanate, 1,6-hexane diisothiocyanate, 1,5-pentane diisothiocyanate, 1,4-butane diisothiocyanate, and 1,3-propane diisothiocyanate.

4. The acid- and alkali-resistant composite nanofiltration membrane according to any one of claims 1-3, wherein, The acid and alkali resistant composite nanofiltration membrane has an average pore size of 0.1-0.5 nm, preferably 0.2-0.4 nm; Preferably, the acid and alkali resistant composite nanofiltration membrane has a molecular weight cutoff of 100-500 Da, more preferably 200-400 Da; Preferably, the contact angle of the acid and alkali resistant composite nanofiltration membrane is 40-80°, and more preferably 40-60°.

5. The acid- and alkali-resistant composite nanofiltration membrane according to any one of claims 1-4, wherein, The thickness of the bottom layer is 30-150μm, preferably 50-120μm; Preferably, the thickness of the porous support layer is 10-100 μm, and more preferably 30-60 μm; Preferably, the thickness of the polyurea-thiourea separation layer is 10-500 nm, and more preferably 50-300 nm.

6. A method for preparing an acid- and alkali-resistant composite nanofiltration membrane, characterized in that, The preparation method includes the following steps: S1. Prepare a porous support layer on the bottom layer; S2. The membrane layer obtained in step S1 is first contacted with an aqueous phase containing polyamines, and then second contacted with an organic phase containing polyisocyanates and polyisothiocyanates. After heat treatment, the acid and alkali resistant composite nanofiltration membrane is obtained.

7. The preparation method according to claim 6, wherein, The polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, ethylenediamine, 1,2-propanediamine, 1,4-butanediamine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, and polyetheramine; Preferably, the polyisocyanate compound is selected from at least one of the following: isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate, toluene-2,4-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), 1,3-phenyl diisocyanate, 3,3'-dichloro-4,4'-diisocyanate biphenyl, dicyclohexylmethane-4,4'-diisocyanate, trimethylhexamethylene diisocyanate, L-lysine-ethyl ester-diisocyanate, 1,4-cyclohexyl diisocyanate, and 4-chloro-6-methyl isophthalic diisocyanate. Preferably, the polyisothiocyanate is at least one selected from 1,4-phenylene diisothiocyanate, 1,3-phenylene diisothiocyanate, 1,2-phenylene diisothiocyanate, 2,6-toluene diisothiocyanate, 2,3-toluene diisothiocyanate, 2,4-toluene diisothiocyanate, 2,5-toluene diisothiocyanate, 3,5-toluene diisothiocyanate, 1,6-hexane diisothiocyanate, 1,5-pentane diisothiocyanate, 1,4-butane diisothiocyanate, and 1,3-propane diisothiocyanate.

8. The preparation method according to claim 6 or 7, wherein, In the aqueous phase containing polyamines, the content of polyamines is 0.2-10% by weight, preferably 0.5-5% by weight; Preferably, in the organic phase containing polyisocyanates and polyisothiocyanates, the content of the polyisocyanates is 0.005-1% by weight, preferably 0.01-0.2% by weight; the content of the polyisothiocyanates is 0.01-1% by weight, preferably 0.02-0.2% by weight. Preferably, the amounts of the aqueous phase and the organic phase are such that the mass ratio of the polyisocyanate, the polyisothiocyanate and the polyamine is 0.01-1:0.01-1:1, more preferably 0.02-1:0.02-1:

1.

9. The preparation method according to any one of claims 6-8, wherein, The duration of the first contact is 5s-100s, preferably 10s-60s; Preferably, the second contact time is 10s-200s, more preferably 20s-120s; Preferably, the heat treatment conditions include: a heat treatment temperature of 40-150℃, more preferably 50-120℃; and a heat treatment time of 0.5-20 minutes, more preferably 1-10 minutes.

10. An acid- and alkali-resistant composite nanofiltration membrane prepared by any one of claims 6-9.

11. The application of the acid and alkali resistant composite nanofiltration membrane according to any one of claims 1-5 and 10 in the field of water treatment.

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