Nanofiltration membrane and preparation method thereof

Abstract

The invention relates to a nanofiltration membrane and a preparation method thereof. The nanofiltration membrane sequentially comprises a supporting material and a membrane body from bottom to top, the base film is formed by a base film solution containing a polymer with a polyimide structure, a nano material and a silane coupling agent containing at least one functional group of a primary amino group, a secondary amino group and an epoxy group; the functional layer is formed by treating a prepolymer of aliphatic polyamine and aromatic polyisocyanate with more than three isocyanate groups with an aqueous solution containing hyperbranched polyamine and strong alkali and weak acid salt; the molar amount of the aromatic polyisocyanate having more than three isocyanate groups is excessive relative to the molar amount of the aliphatic polyamine, the prepolymer has unreacted isocyanate groups, the prepolymer is prepared at a temperature range of 10-20 DEG C, and the treatment is carried out at a temperature range of 50-80 DEG C. The nanofiltration membrane can tolerate a temperature of 70 DEG C or above and a high-concentration alkali of 20 wt% or above, and has excellent salt rejection rate and flux.

Description

Technical Field

[0001] The present invention relates to a nanofiltration membrane, and more particularly to the field of high-temperature and alkali-resistant nanofiltration membranes. Background Art

[0002] With the intensification of diversified market applications, the demand scale for high-temperature material separation and sewage resource utilization in the domestic industrial field is increasing day by day. Actively promoting the realization of efficient energy conservation and emission reduction in the industrial field to achieve the dual-carbon goal has become one of the major strategic tasks facing China's ecological civilization construction. Compared with the normal-temperature separation process, on-line high-temperature feed liquid separation does not require additional heat exchange steps, which plays a positive role in saving energy consumption, improving the separation efficiency of water resources and recycling.

[0003] However, practice shows that traditional organic membrane materials have poor high-temperature resistance and can usually only be used below 50°C. Under harsh application conditions, phenomena such as chemical bond breakage, swelling, and membrane performance deterioration are likely to occur, resulting in the loss of membrane use performance. Especially when facing high-temperature and high-concentration alkaline substances, the failure speed will increase rapidly.

[0004] Some current research works improve the thermal stability of nanofiltration membranes by using polymer materials with heat-resistant structures or introducing nanomaterials with good heat resistance.

[0005] Publication No. CN114432902A discloses a high-temperature resistant composite nanofiltration membrane, where the base membrane and the separation layer are ceramic materials and sulfonated polyaryletherketone respectively, and the nanofiltration membrane has both excellent high-temperature resistance and separation effect. Publication No. CN116899419B discloses a high-temperature resistant nanofiltration membrane based on a nanomaterial intermediate layer, where the base membrane and the functional layer materials are polyethersulfone and polyamide respectively, and the intermediate layer is an amino-silane modified hydroxy nanomaterial, and the nanofiltration membrane can maintain the stability of its structure and performance at a high temperature of 90°C. The literature P. Wen, Y. Chen, X. Hu, et al. Polyamide thin film composite nanofiltration membrane modified with acyl chlorided graphene oxide. J Membr. Sci. 2017, 535, 208 - 220 adds graphene oxide to the polyamide separation layer to improve the thermal stability of the nanofiltration membrane.

[0006] In addition, Patent Publication No. CN115364680B discloses an alkali-resistant nanofiltration membrane. By adding aminated lignin in the aqueous phase, the energy barrier of alkali hydrolysis is increased, thereby improving its alkali resistance. The nanofiltration membrane is soaked for 8 days under the condition of pH 13, and its basic performance remains stable. Patent No. US9943811B2 discloses that AMS Company has developed a composite nanofiltration membrane resistant to acids, alkalis and solvents. The separation layer material thereof is polyamine, which is prepared by interfacial polymerization of polyamine and cyanuric chloride or its derivatives, and has strong stability in a strong alkali environment.

[0007] In the prior art, only one of the characteristics of high temperature resistance and high-concentration alkali resistance has been concerned, and only nanofiltration membrane materials with only one of high temperature resistance and high-concentration alkali resistance have been provided. The characteristics of high temperature resistance and high-concentration alkali resistance have not been concerned and solved simultaneously.

[0008] Existing commercially available alkali-resistant nanofiltration membranes do not have high temperature resistance. Under high temperature conditions (70 - 80 °C), the functional layer is damaged within a short period of time (2 - 3 weeks) during operation, and defects such as red spots and cracks appear on the membrane material, completely losing its use performance, indicating that the membrane material has serious deficiencies in tolerance to high temperatures.

[0009] In addition, the preparation processes of existing alkali-resistant nanofiltration membranes are all two-step methods. That is, an aqueous phase solution and an organic phase solution are prepared separately in advance, and then the base membrane is treated with the aqueous phase and the organic phase respectively. Before immersing the membrane into the organic phase solution after being treated with the aqueous phase solution, a series of processes such as blowing air on the membrane surface and sucking air on the back of the membrane are required to keep the membrane surface dry. The process is relatively complex, with high resource consumption and production costs, and the process conditions are harsh, which is not conducive to industrial scale production and cost reduction and efficiency improvement.

[0010] In addition, the existing high temperature-resistant or alkali-resistant nanofiltration membranes have low desalination rates or low fluxes, which cannot meet the actual application requirements. Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] The purpose of the present invention is to solve the technical problem that existing nanofiltration membrane materials cannot simultaneously meet the tolerance to high temperatures (such as above 70 °C) and high-concentration alkalis (such as above 20 wt%), and to provide a nanofiltration membrane with both high temperature resistance and high-concentration alkali resistance and excellent desalination rate and flux.

[0013] The purpose of the present invention is also to optimize the existing preparation process, reduce the process complexity and production costs, and improve the production efficiency.

[0014] Solutions for Solving the Problems

[0015] In order to solve the above problems existing in the prior art, the inventors of the present invention have conducted in-depth research and found that: using a polymer containing a polyimide structure as the main material of the base film solution, and adding a nanomaterial and a silane coupling agent containing at least one functional group among primary amino groups, secondary amino groups, and epoxy groups can not only improve the hydrophilicity of the base film to increase the flux, but also improve the dispersion of the nanomaterial in the base film, and can also promote the orderly adsorption of amine substances in the subsequent stage to improve the uniformity of the distribution of amine substances. In addition, the specific silane coupling agent as described above can react with the polymer containing a polyimide structure to form a three-dimensional network cross-linked structure, thereby endowing high temperature resistance, high concentration alkali resistance, and improving the rejection rate.

[0016] The inventors also found that: first prepare a prepolymer of an aliphatic polyamine and an aromatic polyisocyanate having three or more isocyanate groups in the temperature range of 10-20 °C, then form a prepolymer coating on the surface of the base film, and then treat it with an aqueous solution containing a hyperbranched polyamine and a weak base strong acid salt in the temperature range of 50 °C to 80 °C. This can not only form a "double cross-linked" interpenetrating network between the base film and the functional layer, so that the base film and the functional layer are "integrated", further improving high temperature resistance and high concentration alkali resistance. In addition, through the specific treatment as described above, the cross-linking degree of the functional layer can be further improved, making the functional layer more dense, thereby further improving the desalination effect.

[0017] The present invention provides a nanofiltration membrane, which sequentially includes from bottom to top:

[0018] A support material, which is a non-woven fabric;

[0019] A base film, which is formed from a base film solution containing a polymer having a polyimide structure, a nanomaterial, and a silane coupling agent containing at least one functional group among primary amino groups, secondary amino groups, and epoxy groups;

[0020] A functional layer, which is formed by treating a prepolymer of an aliphatic polyamine and an aromatic polyisocyanate having three or more isocyanate groups with an aqueous solution containing a hyperbranched polyamine and a weak base strong acid salt. The molar amount of the aromatic polyisocyanate having three or more isocyanate groups is in excess of the molar amount of the aliphatic polyamine. The prepolymer has unreacted isocyanate groups. The prepolymer is prepared in the temperature range of 10-20 °C, and the treatment is carried out in the temperature range of 50 °C to 80 °C.

[0021] The nanofiltration membrane of the present invention, wherein the polymer having a polyimide structure is any one or a combination of two or more of polyimide, polyetherimide, polyimide ether sulfone, polybenzimidazole imide, and polyamide imide; preferably, based on the total weight of the base membrane solution, the concentration of the polymer is 15 wt% to 25 wt%, and the molecular weight of the polymer is 10,000 - 100,000 Da; preferably, the nanomaterial is at least one of nano-silica, nano-molybdenum dioxide, nano-zirconium oxide, nano-graphene oxide, carbon nanotubes, nano-titanium dioxide, nano-metal organic framework MOF, nano-covalent organic framework COF, and nano-zeolite organic framework ZOF, and based on the total weight of the base membrane solution, the addition amount of the nanomaterial is 0.01 wt% to 0.1 wt%; preferably, the silane coupling agent containing at least one functional group of primary amine group, secondary amine group, and epoxy group is any one or a combination of two or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, and based on the total weight of the base membrane solution, the addition amount of the silane coupling agent is 0.1 wt% to 1.0 wt%.

[0022] The nanofiltration membrane of the present invention, wherein the base membrane solution further contains a pore-forming agent, preferably, the pore-forming agent is polyvinylpyrrolidone; preferably, based on the total weight of the base membrane solution, the addition amount of the pore-forming agent is 0.5 wt% to 5.0 wt%; preferably, the base membrane solution contains an organic solvent, and the organic solvent is any one or a combination of two or more of N,N'-dimethylformamide (DMF), N,N'-dimethylhexamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0023] The nanofiltration membrane of the present invention, wherein the aliphatic polyamine is any one or a combination of two or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylenetriaminepentaacetic acid, and triethylenetetramine; preferably, based on the total weight of the prepolymer solution, the addition amount of the aliphatic polyamine is 0.1 wt% to 1.0 wt%; preferably, the aromatic polyisocyanate having three or more isocyanate groups is any one or a combination of two or more of triphenylmethane triisocyanate, triphenyl isocyanate thiophosphate, toluene triisocyanate, and hexamethylene diisocyanate isocyanurate trimer; preferably, based on the total weight of the prepolymer solution, the addition amount of the aromatic polyisocyanate having three or more isocyanate groups is 1.0 wt% to 3.0 wt%.

[0024] The nanofiltration membrane described in the present invention, wherein the hyperbranched polyamine is any one or a combination of two or more of polyethyleneimine, polyamide-amine, polymethacrylimide, polyetherimide, and polydopamine; preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the weak base salt, the addition amount of the hyperbranched polyamine is 0.1 wt% to 1.0 wt%; preferably, the weak base salt is any one or a combination of two or more of sodium carbonate, potassium carbonate, sodium acetate, sodium phosphate, potassium phosphate, sodium bicarbonate, sodium sulfite, sodium bisulfite, disodium hydrogen phosphate, and sodium dihydrogen phosphate; preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the weak base salt, the addition amount of the weak base salt is 10 wt% to 20 wt%.

[0025] The present invention also provides a method for preparing a nanofiltration membrane, which includes the following steps:

[0026] Prepare a base membrane solution, which contains a polymer with a polyimide structure, a nanomaterial, and a silane coupling agent containing at least one functional group among primary amine groups, secondary amine groups, and epoxy groups;

[0027] Apply the base membrane solution onto a support material to form a base membrane, and the support material is non-woven fabric;

[0028] In the temperature range of 10 to 20 °C, prepare a prepolymer of an aliphatic polyamine and an aromatic polyisocyanate having three or more isocyanate groups, wherein the molar amount of the aromatic polyisocyanate having three or more isocyanate groups is in excess relative to the molar amount of the aliphatic polyamine, and the prepolymer has unreacted isocyanate groups;

[0029] Apply the prepolymer onto the base membrane to form a prepolymer coating;

[0030] Treat the base membrane with a prepolymer coating formed thereon in the temperature range of 50 °C to 80 °C with an aqueous solution containing a hyperbranched polyamine and a weak base salt;

[0031] Perform post-treatment to obtain a nanofiltration membrane.

[0032] The method of the present invention, wherein the polymer with a polyimide structure is any one or a combination of two or more of polyimide, polyetherimide, polyimide ether sulfone, polybenzimidazole imide, polyamide imide; preferably, based on the total weight of the base film solution, the concentration of the polymer is 15 wt% to 25 wt%, and the molecular weight of the polymer is 10,000 - 100,000 Da; preferably, the nanomaterial is at least one of nano-silica, nano-molybdenum dioxide, nano-zirconium oxide, nano-graphene oxide, carbon nanotubes, nano-titanium dioxide, nano-metal organic framework MOF, nano-covalent organic framework COF, nano-zeolite organic framework ZOF, and based on the total weight of the base film solution, the addition amount of the nanomaterial is 0.01 wt% to 0.1 wt%; preferably, the silane coupling agent containing at least one functional group of primary amine group, secondary amine group and epoxy group is any one or a combination of two or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, and based on the total weight of the base film solution, the addition amount of the silane coupling agent is 0.1 wt% to 1.0 wt%.

[0033] The method of the present invention, wherein the base film solution further contains a pore-forming agent, preferably, the pore-forming agent is polyvinylpyrrolidone; preferably, based on the total weight of the base film solution, the addition amount of the pore-forming agent is 0.5 wt% to 5.0 wt%; preferably, the base film solution contains an organic solvent, and the organic solvent is any one or a combination of two or more of N,N'-dimethylformamide (DMF), N,N'-dimethylhexamide (DMAc), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO).

[0034] The method of the present invention, wherein the aliphatic polyamine is any one or a combination of two or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylenetriaminepentaacetic acid, triethylenetetramine; preferably, based on the total weight of the prepolymer solution, the addition amount of the aliphatic polyamine is 0.1 wt% to 1.0 wt%; preferably, the aromatic polyisocyanate having three or more isocyanate groups is any one or a combination of two or more of triphenylmethane triisocyanate, triphenyl isocyanate thiophosphate, toluene triisocyanate, hexamethylene diisocyanate isocyanurate trimer; preferably, based on the total weight of the prepolymer solution, the addition amount of the aromatic polyisocyanate having three or more isocyanate groups is 1.0 wt% to 3.0 wt%.

[0035] The method according to the present invention, wherein the hyperbranched polyamine is any one or a combination of two or more of polyethyleneimine, polyamide-amine, polymethacrylimide, polyetherimide, and polydopamine; preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the weak base salt, the addition amount of the hyperbranched polyamine is 0.1 wt% to 1.0 wt%; preferably, the weak base salt is any one or a combination of two or more of sodium carbonate, potassium carbonate, sodium acetate, sodium phosphate, potassium phosphate, sodium bicarbonate, sodium sulfite, sodium bisulfite, disodium hydrogen phosphate, and sodium dihydrogen phosphate; preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the weak base salt, the addition amount of the weak base salt is 10 wt% to 20 wt%.

[0036] Effect of the invention

[0037] The nanofiltration membrane of the present invention can withstand temperatures above 70 °C and high-concentration alkalis above 20 wt%, effectively avoiding defects such as red spots and cracks caused by the destruction of the functional layer under high-temperature and high-alkalinity conditions, and having excellent desalination rate and flux, meeting the stringent requirements of online high-temperature feed liquid separation, extending the service life of the nanofiltration membrane, meeting the application requirements of industries such as the chemical fiber industry and the biopharmaceutical industry, and effectively reducing the material separation and treatment costs of related industries.

[0038] The preparation method provided by the present invention effectively reduces the complexity of the preparation process, significantly reduces resource consumption, equipment costs, and production costs, and greatly improves production efficiency. Detailed implementation manners

[0039] The following will detail various exemplary embodiments, features, and aspects of the present invention. The special term "exemplary" here means "serving as an example, embodiment, or illustration". Any embodiment described as "exemplary" here does not have to be construed as superior to or better than other embodiments.

[0040] In addition, to better illustrate the present invention, numerous specific details are given in the following detailed implementation manners. Those skilled in the art should understand that the present invention can be implemented without some specific details. In other instances, methods, means, equipment, and steps well-known to those skilled in the art are not described in detail to highlight the gist of the present invention.

[0041] Unless otherwise stated, the units used in this specification are all international standard units, and the numerical values and numerical ranges appearing in the present invention should be understood to include the inevitable systematic errors in industrial production.

[0042] In this specification, the meaning expressed by "may" includes the meanings of both performing a certain process and not performing a certain process.

[0043] In this specification, the "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", etc. mentioned refer to the specific elements (e.g., features, structures, properties, and / or characteristics) related to the embodiments, which are included in at least one of the embodiments described herein, and may or may not exist in other embodiments. Additionally, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0044] In this specification, the numerical range represented by "numerical value A to numerical value B" refers to a range that includes the endpoint numerical values A and B.

[0045] The present invention provides a nanofiltration membrane, which sequentially includes from bottom to top:

[0046] A support material, which is a non-woven fabric;

[0047] A base film, which is formed from a base film solution containing a polymer having a polyimide structure, a nanomaterial, and a silane coupling agent containing at least one functional group selected from a primary amino group, a secondary amino group, and an epoxy group;

[0048] A functional layer, which is formed by treating a prepolymer of an aliphatic polyamine and an aromatic polyisocyanate having three or more isocyanate groups with an aqueous solution containing a hyperbranched polyamine and a weak base salt. The molar amount of the aromatic polyisocyanate having three or more isocyanate groups is in excess of the molar amount of the aliphatic polyamine. The prepolymer has unreacted isocyanate groups. The prepolymer is prepared in a temperature range of 10 to 20 °C, and the treatment is carried out in a temperature range of 50 °C to 80 °C.

[0049] By using a polymer containing a polyimide structure as the main material of the base film solution and adding a nanomaterial, the high-temperature resistance property can be imparted. In addition, by introducing a silane coupling agent containing at least one functional group selected from a primary amino group, a secondary amino group, and an epoxy group, the alkoxy groups contained in the silane coupling agent are easily hydrolyzed to generate hydroxyl groups, which can improve the hydrophilicity of the base film and thus increase the flux. Moreover, the specific functional groups contained in the silane coupling agent can improve the dispersion of the nanomaterial in the base film, promote the uniform dispersion of the nanomaterial in the base film, and can also promote the orderly adsorption of amine substances in the subsequent stage to improve the uniformity of the distribution of amine substances. In addition, the specific silane coupling agent as described above can react with the polymer containing a polyimide structure to form a three-dimensional network cross-linked structure, thereby imparting high-temperature resistance, high-concentration alkali resistance, and improving the rejection rate.

[0050] Preferably, the polymer with a polyimide structure is any one or a combination of two or more of polyimide, polyetherimide, polyimide ether sulfone, polybenzimidazole imide, and polyamide imide.

[0051] Preferably, based on the total weight of the base film solution, the concentration of the polymer is 15 wt% to 25 wt%, more preferably, the concentration is 18 wt% to 22 wt%, and further preferably, the concentration is 19 wt% to 21 wt%.

[0052] Preferably, the molecular weight of the polymer is 10,000 - 100,000 Da, more preferably, the molecular weight is 30,000 - 80,000 Da, and further preferably, 40,000 - 80,000 Da.

[0053] Preferably, the nanomaterial is at least one of nano-silica, nano-molybdenum dioxide, nano-zirconium oxide, nano-graphene oxide, carbon nanotubes, nano-titanium dioxide, nano-metal-organic framework MOF, nano-covalent organic framework COF, and nano-zeolite organic framework ZOF.

[0054] Preferably, the particle sizes of nano-silica, nano-molybdenum dioxide, nano-zirconium oxide, and nano-titanium dioxide are in the range of 50 - 100 nm, the aspect ratio of carbon nanotubes is in the range of 10:1 - 50:1, the particle size of nano-graphene oxide is in the range of 300 - 500 nm, and the particle sizes of nano-metal-organic framework MOF, nano-covalent organic framework COF, and nano-zeolite organic framework ZOF are in the range of 100 - 200 nm.

[0055] Preferably, the nano-metal-organic framework MOF is at least one of Zr-MOF, Fe-MOF, and UiO-66-MOF.

[0056] Preferably, based on the total weight of the base film solution, the addition amount of the nanomaterial is 0.01 wt% to 0.1 wt%, more preferably, the addition amount is 0.03 wt% to 0.08 wt%.

[0057] Preferably, the silane coupling agent containing at least one functional group of primary amine group, secondary amine group, and epoxy group is any one or a combination of two or more of γ-aminopropyltriethoxysilane (KH-550), γ-(2,3-epoxypropoxy)propyltrimethoxysilane (KH-560), N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane (KH-792), and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane (KH-602).

[0058] Preferably, based on the total weight of the base film solution, the addition amount of the silane coupling agent is 0.1 wt% to 1.0 wt%, and more preferably, the addition amount is 0.4 wt% to 0.8 wt%.

[0059] Preferably, the base film solution further contains a pore-forming agent. More preferably, the pore-forming agent is polyvinylpyrrolidone PVP. There is no particular limitation on its specific type. For example, any one or a combination of two or more of PVP-K10, PVP-K15, PVP-K30, PVP-K60, and PVP-K90 can be used.

[0060] Preferably, based on the total weight of the base film solution, the addition amount of the pore-forming agent is 0.5 to 5.0 wt%, and more preferably, the addition amount is 2.0 to 5.0 wt%.

[0061] Preferably, the base film solution further contains an organic solvent. There is no particular limitation on the type of the organic solvent as long as it can dissolve the polymer having a polyimide structure. More preferably, the organic solvent is any one or a combination of two or more of N,N'-dimethylformamide (DMF), N,N'-dimethylhexamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0062] There is no particular limitation on the material of the non-woven fabric, and non-woven fabrics made of materials such as polypropylene PP and polyethylene PE can be used.

[0063] By preparing a prepolymer of an aliphatic polyamine and an aromatic polyisocyanate having three or more isocyanate groups in the temperature range of 10 to 20 °C, since the isocyanate groups have relatively low activity in such a temperature range, usually only one or two isocyanate groups react with the polyamine to form a prepolymer. Therefore, the prepolymer has unactivated or unreacted isocyanate groups. By carrying out treatment in the presence of a subsequent weak base salt and in the temperature range of 50 °C to 80 °C, the weak base salt acts as an activator to reduce the reaction potential energy of the unactivated or unreacted isocyanate groups, further activate their reaction activity, promote the perfection degree of the prepolymer layer, and also promote the reaction of the unactivated or unreacted isocyanate groups with the silane coupling agent in the base film, enabling the "integration" of the base film and the functional layer to form a "double crosslinked" interpenetrating network structure, further enhancing the high temperature resistance effect and the resistance to high-concentration alkali.

[0064] In addition, by making the molar amount of the aromatic polyisocyanate having three or more isocyanate groups in excess relative to the molar amount of the aliphatic polyamine, the prepolymer solution still contains an excess of unreacted aromatic polyisocyanate having three or more isocyanate groups. Such an excess of aromatic polyisocyanate can react with the hyperbranched polyamine in the presence of a subsequent weak base salt and within a temperature range of 50°C to 80°C, making the crosslinking of the functional layer more perfect, making the functional layer denser, and further enhancing the desalination effect.

[0065] Within a temperature range of 50°C to 80°C and in the presence of a weak base salt, the diffusion rate of the hyperbranched polyamine can be increased and its permeability in the prepolymer layer can be enhanced, promoting its full reaction with the excess unreacted aromatic polyisocyanate having three or more isocyanate groups in the prepolymer layer, further converting the prepolymer into a high polymer, enhancing the density and crosslinking degree of the functional layer, perfecting the structure of the functional layer, and achieving the purpose of further improving the desalination effect.

[0066] Preferably, the aliphatic polyamine is any one or a combination of two or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylenetriaminepentaacetic acid, and triethylenetetramine.

[0067] Preferably, based on the total weight of the prepolymer solution, the addition amount of the aliphatic polyamine is 0.1 wt% to 1.0 wt%, and more preferably, the addition amount is 0.6 wt% to 0.8 wt%.

[0068] Preferably, the aromatic polyisocyanate having three or more isocyanate groups is any one or a combination of two or more of triphenylmethane triisocyanate, triphenyl isocyanate thiophosphate, toluene triisocyanate, and hexamethylene diisocyanate isocyanurate trimer.

[0069] Preferably, based on the total weight of the prepolymer solution, the addition amount of the aromatic polyisocyanate having three or more isocyanate groups is 1.0 wt% to 3.0 wt%, and more preferably, the addition amount is 2.0 wt% to 2.4 wt%.

[0070] Preferably, the hyperbranched polyamine is any one or a combination of two or more of polyethyleneimine, polyamide-amine, polymethacrylimide, polyetherimide, and polydopamine.

[0071] Preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the weak base salt, the addition amount of the hyperbranched polyamine is 0.1 wt% to 1.0 wt%, and more preferably, the addition amount is 0.6 wt% to 0.9 wt%.

[0072] Preferably, the molecular weight of the hyperbranched polyamine is 5000 - 30000 Da, and more preferably, the molecular weight is 6000 - 20000 Da.

[0073] Preferably, the strong base weak acid salt is any one or a combination of two or more of sodium carbonate, potassium carbonate, sodium acetate, sodium phosphate, potassium phosphate, sodium bicarbonate, sodium sulfite, sodium bisulfite, disodium hydrogen phosphate, and sodium dihydrogen phosphate.

[0074] Preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the strong base weak acid salt, the addition amount of the strong base weak acid salt is 10 wt% - 20 wt%, and more preferably, the addition amount is 15 wt% - 20 wt%.

[0075] The present invention also provides a method for preparing the above nanofiltration membrane, which includes the following steps:

[0076] Prepare a base membrane solution, which contains a polymer with a polyimide structure, a nanomaterial, and a silane coupling agent containing at least one functional group of a primary amine group, a secondary amine group, and an epoxy group;

[0077] Apply the base membrane solution onto a support material to form a base membrane, and the support material is a non-woven fabric;

[0078] In the temperature range of 10 - 20 °C, prepare a prepolymer of an aliphatic polyamine and an aromatic polyisocyanate having more than three isocyanate groups, wherein the molar amount of the aromatic polyisocyanate having more than three isocyanate groups is in excess relative to the molar amount of the aliphatic polyamine, and the prepolymer has unreacted isocyanate groups;

[0079] Apply the prepolymer onto the base membrane to form a prepolymer coating;

[0080] Treat the base membrane with a prepolymer coating formed thereon in the temperature range of 50 °C to 80 °C with an aqueous solution containing a hyperbranched polyamine and a strong base weak acid salt;

[0081] Perform post-treatment to obtain a nanofiltration membrane.

[0082] In the traditional preparation process, the base membrane is usually treated with an aqueous solution and an organic solution respectively. Therefore, correspondingly, soaking tanks or spraying equipment and pulling equipment are required. In addition, before immersing in the organic solution after being treated with the aqueous solution, a series of processes such as blowing air on the membrane surface and sucking air on the back of the membrane are also required to keep the membrane surface dry. The processes are relatively complex, the resource consumption and production cost are high, the process conditions are harsh, and it is not conducive to industrial scale production and cost reduction and efficiency improvement.

[0083] Prepared by the above process of the present invention, the above operations and corresponding equipment requirements are eliminated, greatly promoting the continuity of production and process stability, effectively reducing the complexity of the preparation process, correspondingly significantly reducing resource consumption, equipment costs and production costs, and greatly improving production efficiency.

[0084] There is no particular limitation on the method of applying the base film solution onto the support material to form the base film, and the common methods in the art can be adopted. For example, the base film solution is scraped onto a polypropylene (PP) non-woven fabric with a doctor blade, then immersed in a coagulation bath at a temperature of 10 - 15°C, the film scraping speed is, for example, 5 m / min, the exposure time in the coagulation bath is, for example, 15 - 20 seconds, and then rinsed with deionized water to obtain a porous base film (also known as UF membrane) with a thickness of 6.0 ± 0.1 mil.

[0085] There is no particular limitation on the treatment time with an aqueous solution containing hyperbranched polyamine and weak base salt, and it is preferably 5 - 30 min, more preferably 15 - 25 min.

[0086] More preferably, it is treated with an aqueous solution containing hyperbranched polyamine and weak base salt in the temperature range of 60°C to 80°C.

[0087] Examples

[0088] The embodiments of the present invention will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, the operations are carried out under conventional conditions or conditions recommended by the manufacturer. All reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0089] Preparation Example 1

[0090] A solution with a mass concentration of 18% of polyimide (molecular weight 30000 Da) using DMF as the solvent and a mass concentration of 2% of pore-forming agent PVP-K10 in the solution was prepared. The temperature of the coagulation bath was 12°C, the film scraping speed was 5 m / min, and the exposure time in the coagulation bath was 18 seconds. A base film with a thickness of 6.0 mil was scraped onto the PP non-woven fabric with a doctor blade.

[0091] Preparation Example 2

[0092] A base film was obtained in the same manner as in Preparation Example 1, except that a silane coupling agent KH-550 with a mass concentration of 0.2% and nano metal-organic framework Zr-MOF (particle size 120 nm) with a mass concentration of 0.015% were also added to the solution.

[0093] The base membranes obtained in Preparation Examples 1 and 2 were each run for 60 min at a raw water temperature of 70 °C and a pressure of 30 psi. Compared with the base membrane of Preparation Example 1, after the base membrane obtained in Preparation Example 2 was run at a high temperature of 70 °C, the surface crack phenomenon disappeared, showing excellent high-temperature resistance performance.

[0094] In addition, compared with the base membrane of Preparation Example 1, the rejection rate of the base membrane obtained in Preparation Example 2 for bovine serum albumin (molecular weight 67000 Da) increased from 83.71% to 96.82%, and the flux increased from 328.7 L / m 2 h to 461.2 L / m 2 h.

[0095] The comparison between Preparation Example 2 and Preparation Example 1 shows that the addition of nanomaterials and silane coupling agents improved the flux, high-temperature resistance, and rejection rate for bovine serum albumin.

[0096] The base membranes obtained in Preparation Examples 1 and 2 are only base membranes and do not have a functional layer. Therefore, they do not have desalination properties and cannot be subjected to desalination tests.

[0097] Preparation Example 3

[0098] A base membrane was obtained in the same manner as in Preparation Example 2.

[0099] A prepolymer solution was coated on the base membrane, where the mass concentration of diethylenetriamine was 0.1%, the mass concentration of triphenylmethane triisocyanate was 1%, the solvent was n-hexane, and a prepolymer layer was formed at a temperature of 10 °C. Rinsing and pore-preserving drying were carried out.

[0100] At a raw water temperature of 70 °C and a pressure of 100 psi, it was run for 60 min, and there were no erythema or crack defects on the membrane surface. This result shows that the membrane obtained in Preparation Example 3 has high-temperature resistance.

[0101] For the influent with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet was 68.37%, and the flux was 120.4 L / m 2 h.

[0102] This result shows that compared with the base membrane of Preparation Example 2, due to the further addition of a prepolymer layer, it has certain desalination properties. At the same time, due to the presence of the prepolymer layer, the flux is lower than that of the base membrane of Preparation Example 2.

[0103] Example 1

[0104] Prepare a solution with a mass concentration of 18% of polyimide (molecular weight 30000 Da) using DMF as the solvent. In this solution, the mass concentration of the pore-forming agent PVP-K15 is 2%, the mass concentration of the silane coupling agent KH-550 is 0.2%, the mass concentration of the nano metal-organic framework Zr-MOF (particle size 120 nm) is 0.015%, the coagulation bath temperature is 12 °C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and a high-temperature resistant base film with a thickness of 6.0 mil is scraped on the PP non-woven fabric using a doctor blade.

[0105] Coat a prepolymer solution on the above base film, where the mass concentration of diethylenetriamine is 0.2%, the mass concentration of triphenylmethane triisocyanate is 1%, the solvent is n-hexane, and a prepolymer layer is formed at a temperature of 10 °C. After surface drying, immerse it in an aqueous solution with a mass concentration of 0.5% of polymethacrylimide (molecular weight 6000 Da) and a mass concentration of 10% of sodium bicarbonate, and keep it at a temperature of 50 °C for 5 min. Perform rinsing and pore-preserving drying.

[0106] Under the conditions of an original water temperature of 70 °C and a pressure of 100 psi, run for 60 min, and there are no red spot or crack defects on the membrane surface. This result indicates that the nanofiltration membrane obtained in Example 1 has high-temperature resistance.

[0107] For the influent with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet is 88.41%, and the flux is 92.5 L / m 2 h.

[0108] The obtained nanofiltration membrane is statically immersed in a 20% sodium hydroxide aqueous solution at 70 °C for more than 180 days. Under an operating pressure of 100 psi, the flux remains at 98.6 L / m 2 h, the magnesium sulfate removal rate is stable at 84.71%, and there are no microscopic defects (red spots and cracks) on the membrane sheet surface, possessing excellent high-temperature and alkali resistance stability.

[0109] The above performance test results show that the nanofiltration membrane obtained in Example 1 can withstand a high temperature of 70 °C and a high concentration of alkali with a mass concentration of 20%, and has excellent desalination rate and flux.

[0110] Example 2

[0111] Prepare a solution with a mass concentration of 18% of polyimide (molecular weight 30000 Da) using DMF as the solvent. In this solution, the mass concentration of the pore-forming agent PVP-K15 is 2%, the mass concentration of the silane coupling agent KH-550 is 0.2%, the mass concentration of the nano metal-organic framework Zr-MOF (particle size 120 nm) is 0.015%, the coagulation bath temperature is 12 °C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and a high-temperature resistant base film with a thickness of 6.0 mil is scraped on the PP non-woven fabric using a doctor blade.

[0112] Coat a prepolymer solution on the above base film, where the mass concentration of diethylenetriamine is 0.3%, the mass concentration of triphenylmethane triisocyanate is 1.2%, the solvent is n-hexane, and form a prepolymer layer at a temperature of 10°C. After the surface is dry to the touch, immerse it in an aqueous solution with a mass concentration of 0.6% of polymethacrylimide (molecular weight 6000 Da) and a mass concentration of 12% of sodium bicarbonate, and keep it at a temperature of 50°C for 10 min. Carry out rinsing and pore-preserving drying.

[0113] Under the conditions of the raw water temperature being 70°C and the pressure being 100 psi, run for 60 min, and there are no red spot and crack defects on the membrane surface.

[0114] For the influent with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet is 96.37%, and the flux is 80.2 L / m 2 h.

[0115] The obtained nanofiltration membrane is statically immersed in an aqueous solution of sodium hydroxide with a mass concentration of 20% at 70°C for more than 180 days. Under an operating pressure of 100 psi, the flux remains at 87.4 L / m 2 h, the magnesium sulfate removal rate is stable at 94.34%, there are no microscopic defects (red spots and cracks) on the membrane sheet surface, and it has excellent high-temperature and alkali resistance stability.

[0116] The above performance test results show that the nanofiltration membrane obtained in Example 2 can withstand a high temperature of 70°C and a high concentration of alkali with a mass concentration of 20% and has excellent desalination rate and flux.

[0117] Example 3

[0118] Prepare a solution with a mass concentration of 18% of polyimide (molecular weight 30000 Da) using DMF as the solvent. In this solution, the mass concentration of the pore-forming agent PVP-K15 is 2%, the mass concentration of the silane coupling agent KH-550 is 0.2%, the mass concentration of the nano metal-organic framework Fe-MOF (particle size 180 nm) is 0.015%, the coagulation bath temperature is 12°C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and scrape a high-temperature resistant base film with a thickness of 6.0 mil on the PP non-woven fabric through a doctor blade.

[0119] Coat a prepolymer solution on the above base film, where the mass concentration of diethylenetriamine is 0.4%, the mass concentration of triphenylmethane triisocyanate is 1.5%, the solvent is n-hexane, and form a prepolymer layer at a temperature of 12°C. After the surface is dry to the touch, immerse it in an aqueous solution with a mass concentration of 0.6% of polymethacrylimide (molecular weight 6000 Da) and a mass concentration of 15% of sodium sulfite, and keep it at a temperature of 60°C for 10 min. Carry out rinsing and pore-preserving drying.

[0120] Under the conditions of raw water temperature of 70 °C and pressure of 100 psi, running for 60 min, there are no red spots or crack defects on the membrane surface.

[0121] For the influent water with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet is 98.64%, and the flux is 67.4 L / m 2 h.

[0122] After the obtained nanofiltration membrane is statically immersed in an aqueous sodium hydroxide solution with a mass concentration of 20% at 70 °C for more than 180 days, under an operating pressure of 100 psi, the flux remains 73.8 L / m 2 h, the magnesium sulfate removal rate is stable at 97.53%, and there are no microscopic defects (red spots and cracks) on the membrane sheet surface, showing excellent high-temperature and alkali resistance stability.

[0123] The above performance test results show that the nanofiltration membrane obtained in Example 3 can withstand high temperatures of 70 °C and high-concentration alkali with a mass concentration of 20% and has excellent desalination rate and flux.

[0124] Example 4

[0125] Prepare a solution with a mass concentration of 18% of polyimide (molecular weight of 30000 Da) using DMAc as the solvent. The mass concentration of the pore-forming agent PVP-K30 in this solution is 3%, the mass concentration of the silane coupling agent KH-550 is 0.3%, the mass concentration of the nano metal-organic framework Fe-MOF (particle size 180 nm) is 0.02%, the coagulation bath temperature is 12 °C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and a high-temperature resistant base film with a thickness of 6.0 mil is scraped on the PP non-woven fabric by a doctor blade.

[0126] Coat the prepolymer solution on the above base film, where the mass concentration of diethylenetriamine is 0.6%, the mass concentration of triphenylmethane triisocyanate is 1.5%, the solvent is n-hexane, and a prepolymer layer is formed at a temperature of 12 °C. After surface drying, immerse it in an aqueous solution with a mass concentration of 0.6% of polyethyleneimine (molecular weight of 10000 Da) and a mass concentration of 15% of potassium carbonate, and keep it at 60 °C for 10 min. Carry out rinsing and pore-preserving drying.

[0127] Under the conditions of raw water temperature of 70 °C and pressure of 100 psi, running for 60 min, there are no red spots or crack defects on the membrane surface.

[0128] For the influent water with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet is 99.04%, and the flux is 59.1 L / m 2 h.

[0129] The obtained nanofiltration membrane was statically immersed in an aqueous sodium hydroxide solution with a mass concentration of 20% at 70 °C for more than 180 days. Under an operating pressure of 100 psi, the flux remained at 65.1 L / m 2 h, the magnesium sulfate removal rate was stable at 98.77%, and there were no microscopic defects (red spots and cracks) on the membrane surface, showing excellent high-temperature and alkali resistance stability.

[0130] The above performance test results show that the nanofiltration membrane obtained in Example 4 can withstand a high temperature of 70 °C and a high-concentration alkali with a mass concentration of 20%, and has excellent desalination rate and flux.

[0131] Example 5

[0132] Prepare a solution with a mass concentration of 19% of polyimide (molecular weight 30000 Da) using NMP as the solvent. In this solution, the mass concentration of the pore-forming agent PVP-K30 is 3%, the mass concentration of the silane coupling agent γ-(2,3-epoxypropoxy)propyltrimethoxysilane is 0.4%, the mass concentration of nano-molybdenum dioxide (particle size 50 nm) is 0.03%, the coagulation bath temperature is 12 °C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and a high-temperature resistant base film with a thickness of 6.0 mil is scraped on the PP non-woven fabric through a scraper.

[0133] Coat a prepolymer solution on the above base film, where the mass concentration of triethylenetetramine is 0.6%, the mass concentration of triphenyl isocyanate thiophosphate is 2.0%, the solvent is n-hexane, and a prepolymer layer is formed at a temperature of 12 °C. After surface drying, immerse it in an aqueous solution with a mass concentration of 0.7% of polyethyleneimine (molecular weight 10000 Da) and a mass concentration of 15% of sodium phosphate, and keep it at 60 °C for 15 min. Carry out rinsing and pore-preserving drying.

[0134] Under the conditions of a raw water temperature of 70 °C and a pressure of 100 psi, run for 60 min, and there are no red spot and crack defects on the membrane surface.

[0135] For the influent with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane is 99.18%, and the flux is 53.4 L / m 2 h.

[0136] The obtained nanofiltration membrane was statically immersed in an aqueous sodium hydroxide solution with a mass concentration of 20% at 70 °C for more than 180 days. Under an operating pressure of 100 psi, the flux remained at 58.3 L / m 2 h, the magnesium sulfate removal rate was stable at 99.10%, and there were no microscopic defects (red spots and cracks) on the membrane surface, showing excellent high-temperature and alkali resistance stability.

[0137] The above performance test results show that the nanofiltration membrane obtained in Example 5 can withstand high temperatures of 70 °C and high-concentration alkali with a mass concentration of 20%, and has excellent desalination rate and flux.

[0138] Example 6

[0139] Prepare a solution with a mass concentration of 20% of polyimide (molecular weight 30000 Da) using DMSO as the solvent. The mass concentration of the pore-forming agent PVP-K60 in this solution is 4%, the concentration of the silane coupling agent KH-792 is 0.6%, the concentration of nano-zirconia (particle size 80 nm) is 0.05%, the coagulation bath temperature is 12 °C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and a high-temperature resistant substrate film with a thickness of 6.0 mil is scraped on the PP non-woven fabric with a doctor blade.

[0140] Coat the prepolymer solution on the above substrate film, where the mass concentration of tetraethylenepentamine is 0.8%, the mass concentration of tolylene triisocyanate is 2.2%, the solvent is n-hexane, and a prepolymer layer is formed at a temperature of 15 °C. After surface drying, immerse it in an aqueous solution with a mass concentration of 0.8% of polyetherimide (molecular weight 12000 Da) and a mass concentration of 18% of disodium hydrogen phosphate, and keep it at a temperature of 70 °C for 20 min. Carry out rinsing and pore-preserving drying.

[0141] Under the conditions of a raw water temperature of 70 °C and a pressure of 100 psi, run for 60 min, and there are no red spots or crack defects on the membrane surface.

[0142] For the influent with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet is 99.34%, and the flux is 50.7 L / m 2 h.

[0143] The obtained nanofiltration membrane is statically immersed in an aqueous sodium hydroxide solution with a mass concentration of 20% at 70 °C for more than 180 days. Under an operating pressure of 100 psi, the flux remains at 54.2 L / m 2 h, the magnesium sulfate removal rate is stable at 99.25%, and there are no microscopic defects (red spots and cracks) on the membrane sheet surface, having excellent high-temperature and alkali resistance stability.

[0144] The above performance test results show that the nanofiltration membrane obtained in Example 6 can withstand high temperatures of 70 °C and high-concentration alkali with a mass concentration of 20%, and has excellent desalination rate and flux.

[0145] Example 7

[0146] Prepare a solution with a mass concentration of 21% of polyimide (molecular weight 30000 Da) using DMSO as the solvent. In this solution, the mass concentration of the pore-forming agent PVP-K90 is 5%, the mass concentration of the silane coupling agent KH-602 is 0.8%, the mass concentration of the nano covalent organic framework TAPB-PDA-COF ((1,3,5-tris(4-aminophenyl)benzene-p-phthalaldehyde)-COF material, particle size 200 nm) is 0.07%, the coagulation bath temperature is 12 °C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and a high-temperature resistant base film with a thickness of 6.0 mil is scraped on the PP non-woven fabric with a doctor blade.

[0147] Coat the prepolymer solution on the above base film, where the mass concentration of diethylenetriaminepentaacetic acid is 1.0%, the mass concentration of hexamethylene diisocyanate isocyanurate trimer is 2.4%, the solvent is n-hexane, and a prepolymer layer is formed at a temperature of 20 °C. After surface drying, immerse it in an aqueous solution with a mass concentration of 0.9% of polyamide-amine (molecular weight 20000 Da) and a mass concentration of 18% of sodium acetate, and keep it at 70 °C for 25 min. Perform rinsing and pore-preserving drying.

[0148] Under the conditions of an original water temperature of 70 °C and a pressure of 100 psi, run for 60 min, and there are no red spot and crack defects on the membrane surface.

[0149] For the influent with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet is 99.47%, and the flux is 48.2 L / m 2 h.

[0150] The obtained nanofiltration membrane is statically immersed in a 20% sodium hydroxide aqueous solution at 70 °C for more than 180 days. Under an operating pressure of 100 psi, the flux remains at 53.4 L / m 2 h, the magnesium sulfate removal rate is stable at 99.39%, and there are no microscopic defects (red spots and cracks) on the membrane sheet surface, showing excellent high-temperature and alkali resistance stability.

[0151] The above performance test results show that the nanofiltration membrane obtained in Example 7 can withstand a high temperature of 70 °C and a high concentration of alkali with a mass concentration of 20% and has excellent desalination rate and flux.

[0152] Example 8

[0153] Prepare a solution with a mass concentration of 21% of polyimide (molecular weight of 30000 Da) using DMF as the solvent. In this solution, the mass concentration of the pore-forming agent PVP-K60 is 5%, the mass concentration of the silane coupling agent KH-602 is 1.0%, the mass concentration of nano-graphene oxide (particle size of 300 nm) is 0.08%, the coagulation bath temperature is 12 °C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and a high-temperature resistant base film with a thickness of 6.0 mil is scraped on the PP non-woven fabric using a doctor blade.

[0154] Coat the prepolymer solution on the above base film, where the mass concentration of triethylenetetramine is 1.0%, the mass concentration of hexamethylene diisocyanate isocyanurate trimer is 3.0%, the solvent is n-hexane, and at a temperature of 15 °C, a prepolymer layer is formed. After the surface is dry, immerse it in an aqueous solution with a mass concentration of 1.0% of polyamide-amine (molecular weight of 20000 Da) and a mass concentration of 20% of sodium dihydrogen phosphate, and keep it at a temperature of 70 °C for 30 min. Carry out rinsing and pore-preserving drying.

[0155] Under the conditions of an original water temperature of 70 °C and a pressure of 100 psi, run for 60 min, and there are no red spot and crack defects on the membrane surface.

[0156] For the influent with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet is 99.56%, and the flux is 47.7 L / m 2 h.

[0157] The obtained nanofiltration membrane is statically immersed in an aqueous sodium hydroxide solution with a mass concentration of 20% at 70 °C for more than 180 days. Under an operating pressure of 100 psi, the flux remains at 49.1 L / m 2 h, the magnesium sulfate removal rate is stable at 99.42%, and there are no microscopic defects (red spots and cracks) on the membrane sheet surface, showing excellent high-temperature and alkali resistance stability.

[0158] The above performance test results show that the nanofiltration membrane obtained in Example 8 can withstand a high temperature of 70 °C and a high concentration of alkali with a mass concentration of 20% and has excellent desalination rate and flux.

[0159] Example 9

[0160] Prepare a solution with a mass concentration of 20% of polyimide (molecular weight of 30000 Da) using NMP as the solvent. In this solution, the mass concentration of the pore-forming agent PVP-K30 is 5%, the mass concentration of the silane coupling agent KH-602 is 0.8%, the mass concentration of nano-metal-organic framework UiO-66-MOF (particle size of 200 nm) is 0.08%, the coagulation bath temperature is 12 °C, the film scraping speed is 5 m / min, the coagulation bath exposure time is 18 s, and a high-temperature resistant base film with a thickness of 6.0 mil is scraped on the PP non-woven fabric using a doctor blade.

[0161] Coat the prepolymer solution on the above base film, where the mass concentration of triethylenetetramine is 0.8%, the mass concentration of triphenylmethane triisocyanate is 2.4%, the solvent is n-hexane, and form a prepolymer layer at a temperature of 20°C. After surface drying, immerse it in an aqueous solution with a mass concentration of 0.8% of polyethyleneimine (molecular weight 18,000 Da) and a mass concentration of 20% of sodium carbonate, and keep it at 80°C for 20 min. Carry out rinsing and pore-preserving drying.

[0162] Under the conditions of the raw water temperature of 70°C and a pressure of 100 psi, run for 60 min, and there are no red spot and crack defects on the membrane surface.

[0163] For the influent with a magnesium sulfate concentration of 2000 ppm, the desalination rate of the membrane sheet is 99.64%, and the flux is 47.2 L / m 2 h.

[0164] The obtained nanofiltration membrane is statically immersed in an aqueous sodium hydroxide solution with a mass concentration of 20% at 70°C for more than 180 days. Under an operating pressure of 100 psi, the flux remains 48.1 L / m 2 h, the magnesium sulfate removal rate is stable at 99.49%, and there are no microscopic defects (red spots and cracks) on the membrane sheet surface, having excellent high-temperature and alkali resistance stability.

[0165] The above performance test results show that the nanofiltration membrane obtained in Example 9 can withstand a high temperature of 70°C and a high concentration of alkali with a mass concentration of 20% and has excellent desalination rate and flux.

[0166] It should be noted that although the technical solutions of the present invention are introduced by specific examples, those skilled in the art can understand that the present invention should not be limited thereto.

[0167] The various embodiments of the present invention have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations are obvious to those of ordinary skill in the art in the technical field without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other ordinary skilled persons in the technical field to understand the disclosed embodiments.

Claims

1. A nanofiltration membrane, which sequentially includes the following from bottom to top: A support material, which is a non-woven fabric; A base membrane, which is formed from a base membrane solution containing a polymer having a polyimide structure, a nanomaterial, and a silane coupling agent containing at least one functional group among a primary amino group, a secondary amino group, and an epoxy group; A functional layer, which is formed by treating a prepolymer of an aliphatic polyamine and an aromatic polyisocyanate having three or more isocyanate groups with an aqueous solution containing a hyperbranched polyamine and a weak base salt. The molar amount of the aromatic polyisocyanate having three or more isocyanate groups is in excess of the molar amount of the aliphatic polyamine. The prepolymer has unreacted isocyanate groups. The prepolymer is prepared within a temperature range of 10 to 20°C, and the treatment is carried out within a temperature range of 50 to 80°C.

2. The nanofiltration membrane according to claim 1, wherein the polymer having a polyimide structure is any one or a combination of two or more of polyimide, polyetherimide, polyimide ether sulfone, polybenzimidazole imide, and polyamide imide; preferably, based on the total weight of the base membrane solution, the concentration of the polymer is 15 wt% to 25 wt%, and the molecular weight of the polymer is 10,000 - 100,000 Da; preferably, the nanomaterial is at least one of nano-silica, nano-molybdenum dioxide, nano-zirconium oxide, nano-graphene oxide, carbon nanotubes, nano-titanium dioxide, nano-metal organic framework MOF, nano-covalent organic framework COF, and nano-zeolite organic framework ZOF. Based on the total weight of the base membrane solution, the addition amount of the nanomaterial is 0.01 wt% to 0.1 wt%; preferably, the silane coupling agent containing at least one functional group among a primary amino group, a secondary amino group, and an epoxy group is any one or a combination of two or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane. Based on the total weight of the base membrane solution, the addition amount of the silane coupling agent is 0.1 wt% to 1.0 wt%.

3. The nanofiltration membrane according to claim 1 or 2, wherein the base membrane solution further contains a pore-forming agent. Preferably, the pore-forming agent is polyvinylpyrrolidone; preferably, based on the total weight of the base membrane solution, the addition amount of the pore-forming agent is 0.5 wt% to 5.0 wt%; preferably, the base membrane solution contains an organic solvent, and the organic solvent is any one or a combination of two or more of N,N'-dimethylformamide (DMF), N,N'-dimethylhexamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

4. The nanofiltration membrane according to claim 1 or 2, wherein the aliphatic polyamine is any one or a combination of two or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylenetriaminepentaacetic acid, and triethylenetetramine; preferably, based on the total weight of the prepolymer solution, the addition amount of the aliphatic polyamine is 0.1 wt% to 1.0 wt%; preferably, the aromatic polyisocyanate having three or more isocyanate groups is any one or a combination of two or more of triphenylmethane triisocyanate, triphenyl isocyanate thiophosphate, tolylene triisocyanate, and hexamethylene diisocyanate isocyanurate trimer; preferably, based on the total weight of the prepolymer solution, the addition amount of the aromatic polyisocyanate having three or more isocyanate groups is 1.0 wt% to 3.0 wt%.

5. The nanofiltration membrane according to claim 1 or 2, wherein the hyperbranched polyamine is any one or a combination of two or more of polyethyleneimine, polyamide-amine, polymethacrylimide, polyetherimide, and polydopamine; preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the strong base weak acid salt, the addition amount of the hyperbranched polyamine is 0.1 wt% to 1.0 wt%; preferably, the strong base weak acid salt is any one or a combination of two or more of sodium carbonate, potassium carbonate, sodium acetate, sodium phosphate, potassium phosphate, sodium bicarbonate, sodium sulfite, sodium bisulfite, disodium hydrogen phosphate, and sodium dihydrogen phosphate; preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the strong base weak acid salt, the addition amount of the strong base weak acid salt is 10 wt% to 20 wt%.

6. A method for preparing a nanofiltration membrane according to any one of claims 1 to 5, comprising the following steps: Preparing a base membrane solution, the base membrane solution containing a polymer having a polyimide structure, a nanomaterial, and a silane coupling agent containing at least one functional group of a primary amino group, a secondary amino group, and an epoxy group; Applying the base membrane solution onto a support material to form a base membrane, the support material being non-woven fabric; Preparing a prepolymer of an aliphatic polyamine and an aromatic polyisocyanate having three or more isocyanate groups within a temperature range of 10 to 20 °C, wherein the molar amount of the aromatic polyisocyanate having three or more isocyanate groups is in excess relative to the molar amount of the aliphatic polyamine, and the prepolymer has unreacted isocyanate groups; Applying the prepolymer onto the base membrane to form a prepolymer coating; Treating the base membrane having the prepolymer coating formed thereon with an aqueous solution containing a hyperbranched polyamine and a strong base weak acid salt within a temperature range of 50 °C to 80 °C; Performing post-treatment to obtain a nanofiltration membrane.

7. The method according to claim 6, wherein the polymer having a polyimide structure is any one or a combination of two or more of polyimide, polyetherimide, polyimide ether sulfone, polybenzimidazole imide, and polyamide imide; preferably, based on the total weight of the base film solution, the concentration of the polymer is 15 wt% to 25 wt%, and the molecular weight of the polymer is 10,000 - 100,000 Da; preferably, the nanomaterial is at least one of nano-silica, nano-molybdenum dioxide, nano-zirconium oxide, nano-graphene oxide, carbon nanotubes, nano-titanium dioxide, nano-metal organic framework MOF, nano-covalent organic framework COF, and nano-zeolite organic framework ZOF, and based on the total weight of the base film solution, the addition amount of the nanomaterial is 0.01 wt% to 0.1 wt%; preferably, the silane coupling agent containing at least one functional group of primary amino group, secondary amino group, and epoxy group is any one or a combination of two or more of γ-aminopropyltriethoxysilane, γ-(2,3-epoxypropoxy)propyltrimethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, and N-β-(aminoethyl)-γ-aminopropylmethyldimethoxysilane, and based on the total weight of the base film solution, the addition amount of the silane coupling agent is 0.1 wt% to 1.0 wt%.

8. The method according to claim 6 or 7, wherein the base film solution further comprises a pore-forming agent, preferably, the pore-forming agent is polyvinylpyrrolidone; preferably, based on the total weight of the base film solution, the addition amount of the pore-forming agent is 0.5 wt% to 5.0 wt%; preferably, the base film solution contains an organic solvent, and the organic solvent is any one or a combination of two or more of N,N'-dimethylformamide (DMF), N,N'-dimethylhexamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

9. The method according to claim 6 or 7, wherein the aliphatic polyamine is any one or a combination of two or more of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, diethylenetriaminepentaacetic acid, and triethylenetetramine; preferably, based on the total weight of the prepolymer solution, the addition amount of the aliphatic polyamine is 0.1 wt% to 1.0 wt%; preferably, the aromatic polyisocyanate having three or more isocyanate groups is any one or a combination of two or more of triphenylmethane triisocyanate, triphenyl isocyanate thiophosphate, toluene triisocyanate, and hexamethylene diisocyanate isocyanurate trimer; preferably, based on the total weight of the prepolymer solution, the addition amount of the aromatic polyisocyanate having three or more isocyanate groups is 1.0 wt% to 3.0 wt%.

10. The method according to claim 6 or 7, wherein the hyperbranched polyamine is any one or a combination of two or more of polyethyleneimine, polyamide-amine, polymethacrylimide, polyetherimide, and polydopamine; preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the weak base salt, the addition amount of the hyperbranched polyamine is 0.1 wt% to 1.0 wt%; preferably, the weak base salt is any one or a combination of two or more of sodium carbonate, potassium carbonate, sodium acetate, sodium phosphate, potassium phosphate, sodium bicarbonate, sodium sulfite, sodium bisulfite, disodium hydrogen phosphate, and sodium dihydrogen phosphate; preferably, based on the total weight of the aqueous solution containing the hyperbranched polyamine and the weak base salt, the addition amount of the weak base salt is 10 wt% to 20 wt%.