A nanofiltration membrane having a silanol three-dimensional network interlayer and a method of making the same

Abstract

The application relates to a nanofiltration membrane with a silanol three-dimensional network intermediate layer, which comprises a base film material layer, an intermediate layer and a polyamide active separation layer; the intermediate layer is a silanol three-dimensional network intermediate layer formed by mixing and intertwining silanol and amine polymers; and the polyamide active separation layer is a surface layer formed by the interfacial polymerization reaction of the amine polymers in the intermediate layer and amine monomers in the aqueous phase solution and acyl chloride monomers in the oil phase solution. The silanol three-dimensional network intermediate layer formed on the base film material can provide a relatively loose interface platform for the interfacial polymerization reaction, make the surface of the polyamide layer more rough, and make the polyamide active separation layer of the surface layer have unique morphology and properties due to the existence of the intermediate layer, including a separation pore size which can change with the size of the operating pressure, which is helpful to improve the water production of the nanofiltration membrane. According to actual production needs, the structure and morphology of the intermediate layer can be adjusted to achieve the purpose of adjusting the performance of the nanofiltration membrane.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite membranes, in particular to a nanofiltration membrane with a silanol three-dimensional network intermediate layer and a preparation method thereof. BACKGROUND

[0002] Due to the vigorous development of new energy industry, the global demand for lithium resources is rapidly growing. With the substantial decrease of land lithium resources, recycling lithium in water resources has become a development trend today. Nanofiltration is a new type of pressure-driven membrane technology developed from reverse osmosis membranes, and based on the separation advantage of the membrane itself, it has become an effective method for separating magnesium and lithium from salt lakes. The nanofiltration membrane has a nanoscale pore size and a molecular weight cut-off of 200-1000 Da, and is the core component of nanofiltration technology. When in contact with the solution, the functional groups on the surface of the nanofiltration membrane will ionize and adsorb charged solutes to generate charges, thereby having a significant separation effect on solute ions of different valence states. At present, nanofiltration membranes are usually prepared by interfacial polymerization of amine monomers and acyl chloride monomers on a porous support layer, and the polyamide functional separation layer formed on the surface mostly has strong negative charge. Although the negatively charged nanofiltration membrane can effectively alleviate the pollution of most microorganisms and natural organic matter (most of which are negatively charged), the strong negative charge itself is not conducive to the separation of magnesium and lithium in salt lakes. Therefore, the common method is to adjust the surface potential of the nanofiltration membrane by modifying with positively charged monomers or introducing positively charged additives, which can improve the magnesium-lithium separation coefficient in salt lakes to a certain extent, but this method not only has a complex process flow, but also the prepared nanofiltration membrane has yet to improve the stability of magnesium rejection.

[0003] In summary, the current negatively charged nanofiltration membrane has weak separation ability for magnesium and lithium, and the positively charged nanofiltration membrane is prone to adsorbing microorganisms and natural organic matter in actual operation, causing membrane pollution and other problems. Therefore, the actual operation environment of membrane separation is complex and harsh, and the simply negatively charged or positively charged nanofiltration membrane is difficult to be applied in the actual membrane separation operation environment for a long time, so higher requirements are put forward for the separation membrane in order to meet the diversification needs in actual production. SUMMARY

[0004] (I) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present application provides a preparation method of a nanofiltration membrane with a silanol three-dimensional network intermediate layer, which can improve the stability of the membrane separation functional layer, increase the rejection rate of magnesium ions, and thus improve the comprehensive performance of the nanofiltration membrane in magnesium-lithium separation, and can adjust the structure of the intermediate layer to change the morphology of the separation layer according to the environmental requirements, so as to meet the diversification needs in actual production.

[0006] (II) Technical solutions

[0007] In a first aspect, the present application also relates to a nanofiltration membrane with a silanol three-dimensional network intermediate layer, comprising a base membrane material layer, an intermediate layer and a polyamide active separation layer; the intermediate layer is a silanol three-dimensional network intermediate layer formed by mixing and intertwining silanol and amine polymers; and the polyamide active separation layer is a surface layer formed by interfacial polymerization between the amine polymers in the intermediate layer and amine monomers in an aqueous phase solution and acyl chloride monomers in an oil phase solution.

[0008] In a second aspect, the present application provides a preparation method of a nanofiltration membrane with a silanol three-dimensional network intermediate layer, comprising:

[0009] S1, pretreatment

[0010] coating the silanol / amine polymer modification liquid onto the base membrane material, removing the excess modification liquid, and forming a silanol three-dimensional network intermediate layer on the base membrane material;

[0011] The preparation method of the silanol / amine polymer modification liquid is as follows: dissolving a silanol precursor in a mixture of water and ethanol, adjusting the pH to be acidic, heating and stirring to make the silanol precursor undergo hydrolysis and recondensation to form a silanol network structure, and then adding at least one amine polymer to make it mix and intertwine with the silanol network structure to obtain the silanol / amine polymer modification liquid.

[0012] S2, interfacial polymerization

[0013] coating the aqueous phase solution containing amine monomers and the oil phase solution containing acyl chloride monomers onto the base membrane material with the silanol three-dimensional network intermediate layer in sequence, and performing heat treatment to complete the interfacial polymerization and generate a polyamide crosslinked network layer, which together with the silanol three-dimensional network intermediate layer forms the functional separation layer of the nanofiltration membrane.

[0014] According to a preferred embodiment of the present application, in S1, the silanol precursor is one or a combination of two or more of tetraethyl orthosilicate, aminopropyltriethoxysilane and silicon tetrachloride; and the mass fraction of the silanol precursor in the modification liquid is 0.5%-5%.

[0015] According to a preferred embodiment of the present application, in S1, the mixed mass ratio of water and ethanol in the mixture of water and ethanol is 10-2:1.

[0016] According to a preferred embodiment of the present application, in S1, in the preparation process of the silanol / amine polymer modification liquid:

[0017] Preferably, the pH is adjusted to be 2-6, preferably 3-5;

[0018] Preferably, the pH is adjusted to be acidic by adding an inorganic acid; and the inorganic acid is at least one of hydrochloric acid, sulfuric acid, nitric acid, boric acid, carbonic acid and phosphoric acid.

[0019] Preferably, the heating temperature is 35-75℃, and more preferably 40-70℃;

[0020] Preferably, the stirring time is 30-90 minutes and the stirring speed is 200-500 rpm.

[0021] According to a preferred embodiment of the present invention, in S1, the amine polymer is at least one selected from polyethyleneamine, polyallylamine, polyethyleneimine, polyacrylamide, and polyamidoamine; the mass fraction of the amine polymer in the modifying solution is 0.5%-3%.

[0022] Preferably, after adding the amine polymer, the amine polymer is mixed and intertwined with the silanol network structure by continuing to stir or heating and stirring to obtain the silanol / amine polymer modified liquid; the stirring time is 15-50 min.

[0023] According to a preferred embodiment of the present invention, in S1, the coating method includes any one of drip coating, brush coating, or dip coating to uniformly transfer the silanol / amine polymer modified liquid onto the base film material.

[0024] According to a preferred embodiment of the present invention, in S1, the substrate material is any one of polysulfone substrate, polyethersulfone substrate, polyvinylidene fluoride substrate, polytetrafluoroethylene substrate, and polyacrylonitrile substrate; each substrate is composed of nonwoven fabric and an ultrafiltration layer. For example, a polysulfone substrate is formed by laminating a nonwoven fabric and a polysulfone ultrafiltration layer, while a polyethersulfone substrate is formed by laminating a nonwoven fabric and a polyethersulfone ultrafiltration layer; other substrates are formed in the same manner.

[0025] According to a preferred embodiment of the present invention, in S2, the amine monomer in the aqueous solution of the interfacial polymerization reaction is one or a combination of two or more of piperazine, diaminodipropylamine, ethylenediamine, diethylenetriamine, 2,5-dimethylpiperazine, m-phenylenediamine, p-phenylenediamine, and o-phenylenediamine, and the mass fraction of the amine monomer in the aqueous solution is 0.1%-5%; more preferably, it is diethylenetriamine, which can make the membrane positively charged.

[0026] Preferably, an acid-absorbing agent is also added to the aqueous solution. This acid-absorbing agent (acid-binding agent) is an alkaline metal salt, such as one or more of potassium phosphate, sodium carbonate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, sodium hydroxide, potassium hydroxide, and triethylamine, with a mass concentration of 0-3%. The acid-absorbing agent can react with the hydrochloric acid produced during the interfacial polymerization process, neutralizing the hydrochloric acid and promoting the interfacial polymerization reaction. Since both piperazine and polyethylenepolyamine have acid-binding properties (reacting with H+),... +Therefore, the piperazine or polyethylene polyamine can participate in the polymerization reaction as a polymerization monomer while itself also acts as an acid-binding agent and is neutralized with hydrogen ions by slightly increasing the concentration of the piperazine or polyethylene polyamine.

[0027] According to a preferred embodiment of the present application, in S2, the acyl chloride monomer in the oil phase solution of the interfacial polymerization reaction is one or a combination of more than one of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride, and isophthaloyl chloride, and the mass fraction of the acyl chloride monomer in the oil phase solution is 0.05%-3%; more preferably, the acyl chloride monomer is trimesoyl chloride, and the mass fraction in the oil phase solution is 0.1%-1%. Preferably, the solvent of the oil phase solution is not limited and is an oil agent used in the interfacial polymerization reaction, and specifically can be one or a mixture of several of Isopar L, Isopar G, Isopar M, Isopar E, n-hexane, and cyclohexane.

[0028] According to a preferred embodiment of the present application, in S2, the coating method includes any one of drop coating, brush coating, and dip coating.

[0029] According to a preferred embodiment of the present application, in S2, the heat treatment temperature is 40-140℃. The heat treatment includes controlled heating using an oven, a hot plate, or a water bath. Preferably, the heat treatment temperature and time are controlled according to the solvent of the oil phase solution selected: if the solvent of the oil phase solution is n-hexane (boiling point 69℃), the heat treatment temperature ranges from 40-100℃, and the treatment time is 2-6 min; if it is Isopar G (initial boiling point 163℃), the heat treatment temperature ranges from 60-120℃, and the treatment time is 2-6 min; if it is Isopar L (initial boiling point 185℃), the heat treatment temperature ranges from 80-140℃, and the treatment time is 2-6 min; under the aforementioned heat treatment conditions, the prepared nanofiltration membrane has good performance.

[0030] According to the preferred embodiment of the present application, the process in S1 is: dissolving at least one silanol precursor of tetraethyl orthosilicate, aminopropyl triethoxysilane and silicon tetrachloride in a solution of water and ethanol with a mass ratio of 10-2:1, adding acid to adjust the pH to 3-5, heating to 35-75℃, stirring at 200-500 rpm for 30 min-90 min, hydrolyzing and recondensing the silanol precursor into a silanol network structure under acidic conditions, then adding at least one amine polymer of polyvinylamine, polyallylamine, polyethyleneimine, polyacrylamide and polyamidoamine, continuing to stir for 15-50 min, mixing and entangling the amine polymer with the silanol network structure to obtain a modified liquid; in the modified liquid, the concentration of the silanol precursor is 0.5%-5% (preferably 1-4%), and the concentration of the amine polymer is 0.5%-3% (preferably 0.2-2%); coating the modified liquid on the base film material, standing for 1-15 min, removing the excess modified liquid, drying, and forming a silanol three-dimensional network intermediate layer on the base film material. The molecular weight of the amine polymer in the present application is 600-70000. By adding the amine polymer to the modified liquid, the amine polymer can be entangled and hydrogen-bonded with the molecular chains of the silanol network structure, and the amine polymer can also participate in the interfacial polymerization reaction in S2, which can strengthen the firmness of the binding between the intermediate layer and the surface of the polyamide active separation layer. In addition, in addition to physical entanglement, the amine polymer itself and the silanol can also undergo hydrogen bonding.

[0031] The amine monomer is not suitable for being directly added to the modified liquid, and the amine monomer has strong basicity and is easy to neutralize with inorganic acid to adjust the pH, which makes it difficult to reach the conditions for hydrolysis and recondensation of the silanol precursor, and also affects the interfacial polymerization reaction of the amine monomer and the acid chloride.

[0032] According to the preferred embodiment of the present application, the process in S2 is: coating the aqueous solution on the base film material with the silanol three-dimensional network intermediate layer, removing the excess aqueous solution after 30-90 s, blowing dry or air drying, then coating the oil phase solution on the dried base film material, removing the excess oil phase solution after 20-40 s, and transferring to an oven for heat treatment at 40℃-140℃ for 2-10 min.

[0033] The aqueous phase solution is formed by dissolving at least one amine monomer selected from the group consisting of piperazine, diaminodipropylamine, ethylenediamine, diethylenetriamine, 2,5-dimethylpiperazine, m-phenylenediamine, p-phenylenediamine and o-phenylenediamine in water to form an aqueous phase solution with a concentration of 0.1% to 5% (preferably 0.5% to 2.5%), preferably diethylenetriamine, to make the membrane positively charged; 0 to 3% of an acid absorber is added to the aqueous phase solution; the oil phase solution is formed by dissolving at least one acyl chloride monomer selected from the group consisting of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride and isophthaloyl chloride in an oil agent to form an oil phase solution with a concentration of 0.05% to 3% (preferably 0.1% to 1%); the oil agent is one or a mixture of several of Isopar L, Isopar G, Isopar M, Isopar E, n-hexane and cyclohexane.

[0034] In a third aspect, the present application also relates to a nanofiltration membrane with a silanol three-dimensional network intermediate layer, which is prepared by the method of any one of the above embodiments.

[0035] (III) Beneficial Effects

[0036] (1) The present application forms a silanol network structure through the hydrolysis and condensation reaction of a silanol precursor, mixes and intertwines with an amine polymer, and reacts through hydrogen bonding, to obtain a modified liquid. After the modified liquid is coated on a base membrane material and dried, a silanol three-dimensional network intermediate layer is obtained on the base membrane material. The intermediate layer can provide a relatively loose interface platform for interfacial polymerization, so that the polyamide separation layer has unique morphology and properties, such as a separation pore size that can change with the size of the operating pressure, which helps to improve the water production of the nanofiltration membrane. The presence of the silanol three-dimensional network intermediate layer can make the surface of the polyamide layer more rough, thereby increasing the contact area of the membrane surface and further improving the water flux.

[0037] By adjusting the concentration of the silanol precursor, the stirring temperature, the stirring time, the stirring speed, the amount of the amine polymer added, and the like during the preparation of the modified liquid, silanol three-dimensional network intermediate layers with different physicochemical parameters can be obtained. Furthermore, the structure of the intermediate layer can be adjusted to change the morphology of the separation layer according to environmental requirements, to meet the diversified needs in actual production. For example, when the magnesium-lithium ratio in the brine is high (usually the osmotic pressure is high), a silanol three-dimensional network intermediate layer with a larger degree of looseness can be obtained by increasing the concentration of the silanol precursor, reducing the reaction temperature, shortening the stirring time, and increasing the stirring speed between 200 rpm and 500 rpm.

[0038] (2) The silanol three-dimensional network intermediate layer of the present invention has abundant hydroxyl groups, which improves the hydrophilicity of the membrane and helps to increase water flux. After the formation of the silanol network structure in the modification solution, amine polymers are added. The amine polymers and the silanol network structure can mix, intertwine, and form hydrogen bonds. The amine polymers can also undergo interfacial reactions with acyl chloride monomers, thus making the bond between the silanol three-dimensional network intermediate layer and the surface polyamide layer stronger. The silanol three-dimensional network intermediate layer is composed of silanol and amine polymers and contains abundant hydroxyl and amine functional groups, which enhance the bonding stability between the bottom membrane material and the functional separation layer through hydrogen bonding.

[0039] (3) A certain amount of amine polymer is combined in the silanol three-dimensional network intermediate layer of the present invention. The amine group can enhance the positive charge of the intermediate layer to a certain extent. Based on the repulsion of like charges, it can improve the nanofiltration membrane's ability to retain high-valence ions such as divalent magnesium ions, improve the separation coefficient of monovalent / multivalent ions, and be suitable for more monovalent / multivalent ion separation scenarios. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the nanofiltration membrane with a silanol three-dimensional network intermediate layer according to the present invention. Detailed Implementation

[0041] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] like Figure 1 The diagram shows a schematic of the nanofiltration membrane with a silanol three-dimensional network intermediate layer according to the present invention. The nanofiltration membrane includes a base membrane material layer 1, an intermediate layer 2, and a polyamide active separation layer 3. The base membrane material layer 1 is any one of a polysulfone base membrane, a polyethersulfone base membrane, a polyvinylidene fluoride base membrane, a polytetrafluoroethylene base membrane, and a polyacrylonitrile base membrane. Each base membrane is composed of a nonwoven fabric and an ultrafiltration layer. For example, a polysulfone base membrane is formed by laminating a nonwoven fabric and a polysulfone ultrafiltration layer, while a polyethersulfone base membrane is formed by laminating a nonwoven fabric and a polyethersulfone ultrafiltration layer; other base membranes follow the same principle. The intermediate layer 2 is a silanol three-dimensional network intermediate layer formed by the interweaving of silanol 22 and amine polymer 21. The polyamide active separation layer 3 is a surface layer formed by the interfacial polymerization reaction of the amine polymer 21 in the intermediate layer, amine monomers in the aqueous solution, and acyl chloride monomers in the oil solution. The presence of the silanol three-dimensional network intermediate layer provides a loose interfacial platform for the interfacial polymerization reaction, making the surface of the synthesized polyamide layer rougher, thereby increasing the contact area of ​​the membrane surface and thus improving the water flux.

[0043] The present application prepares a defect-free nanofiltration membrane with a rougher surface, a more closely combined polyamide active separation layer 3 and base membrane material layer 1 by introducing an intermediate layer constructed in the form of a silanol network structure and amine polymer mixing, intertangling and hydrogen bonding on the surface of the base membrane material layer 1, has excellent monovalent / high valence ion separation capacity, can be suitable for long-term and more complex membrane separation scenarios, and solves the defects of current nanofiltration membranes, such as poor ion selectivity and low water flux. The morphology, thickness, looseness and softness of the intermediate layer 2 affect the flatness of the surface of the polyamide active separation layer 3, the hydrophilicity of the nanofiltration membrane, the water flux, the pore size deformation degree under different operating water pressures, etc., so the preparation of the modified liquid can be adjusted to form a silanol three-dimensional network intermediate layer with different morphologies and physicochemical properties on the base membrane material, and the morphology and physicochemical properties of the polyamide active separation layer 3 can be accurately controlled by taking the intermediate layer as an interfacial polymerization reaction platform to meet the needs of different membrane separation scenarios.

[0044] The preparation method of the nanofiltration membrane with a silanol three-dimensional network intermediate layer of the present application needs to prepare a silanol / amine polymer modification liquid, which includes: dissolving at least one silanol precursor of tetraethyl orthosilicate, aminopropyl triethoxysilane and silicon tetrachloride in a solution composed of water and ethanol with a mass ratio of 10-2:1, adding acid to adjust the pH to 3-5, heating to 35-75℃, and stirring at 200-500 rpm for 30-90 min to make the silanol precursor hydrolyze and re-condense into a silanol network structure under acidic conditions, then adding at least one amine polymer of polyvinylamine, polyallylamine, polyethyleneimine, polyacrylamide and polyamidoamine, and continuing to stir for 15-50 min to make the amine polymer mix and intertangle with the silanol network structure to obtain the modification liquid; in the modification liquid, the concentration of the silanol precursor is 0.5%-5% (preferably 1-4%), and the concentration of the amine polymer is 0.5%-3% (preferably 0.2-2%); the modification liquid is coated on the base membrane material, and after standing for 1-15 min, the excess modification liquid is removed, dried, and a silanol three-dimensional network intermediate layer is formed on the base membrane material.

[0045] In order to more clearly set forth the scheme and concept of the present application, the present application will be exemplified below in conjunction with specific examples. In the following examples, the base membrane material is a polysulfone base membrane, which is a self-made base membrane with performance consistent with commercially available base membrane products. The membrane production date to the experimental date is less than 30 days, and during this period, it is stored in a 2% aqueous sodium bisulfite solution. Before preparing the composite nanofiltration membrane, the polysulfone base membrane material is soaked in pure water for 24 h; the molecular weight of the amine polymer in each example is between 600 and 70,000. The oil solvent in the oil phase solution of each example is Isopar L.

[0046] Example 1

[0047] A nanofiltration membrane with a silanol three-dimensional network intermediate layer is prepared in this example by the following method:

[0048] (1) Water and ethanol are uniformly mixed in a mass ratio of 5:1 to obtain a uniform mixture of water and ethanol. The pH value is adjusted to 3 with hydrochloric acid, and the mixture is placed in a magnetic stirrer. Tetraethyl orthosilicate is added to make the mass fraction 1.5%. The stirring temperature is set to 50°C, and the stirring speed is 200 rpm. Stirring is performed for 1 h.

[0049] (2) Continue to add polyethyleneimine to make the mass fraction of polyethyleneimine 0.5%. After continuing to stir for 30 min, a silanol / polyethyleneimine modification solution is obtained.

[0050] (3) A piperazine aqueous solution with a mass fraction of 0.5% (solvent: deionized water) and a trimesoyl chloride oil solution with a mass fraction of 0.2% (solvent: Isopar L) are prepared.

[0051] (4) First, immerse the polysulfone base film in the silanol / polyethyleneimine modification solution uniformly. After 10 min, remove the excess modification solution and dry it in the air to obtain a silanol / polyethyleneimine network intermediate layer. Then, coat the aqueous solution on the polysulfone base film and remove the excess solution after 60 s. Dry it in the air, then coat the oil phase solution on the dried support film. Remove the excess solution after 20 s, and place it in a 100°C oven for 5 min.

[0052] Example 2

[0053] (1) Water and ethanol are uniformly mixed in a mass ratio of 3:1 to obtain a uniform mixture of water and ethanol. The pH value is adjusted to 3 with hydrochloric acid, and the mixture is placed in a magnetic stirrer. Tetraethyl orthosilicate is added to make the mass fraction 2%. The stirring temperature is set to 50°C, and the stirring speed is 200 rpm. Stirring is performed for 40 min.

[0054] (2) Continue to add polyethyleneimine to make the mass fraction of polyethyleneimine 1%. After continuing to stir for 30 min, a silanol / polyethyleneimine modification solution is obtained.

[0055] Steps (3)-(4) are the same as in Example 1.

[0056] Example 3

[0057] A nanofiltration membrane with a silanol three-dimensional network intermediate layer is prepared in this example by the following method:

[0058] (1) Water and ethanol are uniformly mixed in a mass ratio of 4:1 to obtain a uniform mixture of water and ethanol. The pH value is adjusted to 3 with hydrochloric acid, and the mixture is placed in a magnetic stirrer. Tetraethyl orthosilicate is added to make the mass fraction 3%. The stirring temperature is set to 70°C, and the stirring speed is 200 rpm. Stirring is performed for 30 min.

[0059] (2) Continue to add polyallylamine, so that the mass fraction of polyallylamine is 1.5%, continue to stir for 30 min, and then a silanol / polyallylamine modified solution is obtained.

[0060] (3) Prepare a water phase solution of 0.2% piperazine + 0.1% m-phenylenediamine (deionized water as solvent) and an oil phase solution of 0.2% trimesoyl chloride (Isopar L as solvent).

[0061] Step (4) is the same as that in Example 1.

[0062] Example 4

[0063] In this example, based on Example 2, the mass fraction of tetraethyl orthosilicate in the modified solution is increased from 2% to 3.5%, the stirring temperature is increased to 70°C, and the stirring speed is increased to 300 rpm, and the stirring time is still 40 min. The preparation method of the nanofiltration membrane is as follows:

[0064] (1) Mix water and ethanol uniformly in a mass ratio of 3:1 to obtain a uniform mixture of water and ethanol, adjust the pH value to 3 with hydrochloric acid, place it in a magnetic stirrer, and add tetraethyl orthosilicate so that the mass fraction is 3.5%. Set the stirring temperature to 70°C, the stirring speed to 300 rpm, and the stirring time to 40 min.

[0065] (2) Continue to add polyallylamine, so that the mass fraction of polyallylamine is 1.5%, continue to stir for 30 min, and then a silanol / polyallylamine modified solution is obtained.

[0066] (3) Prepare a water phase solution of 0.2% piperazine + 0.1% m-phenylenediamine (deionized water as solvent) and an oil phase solution of 0.2% trimesoyl chloride (Isopar L as solvent).

[0067] Step (4) is the same as that in Example 1.

[0068] Example 5

[0069] The preparation method of the nanofiltration membrane in this example is as follows:

[0070] (1) Mix water and ethanol uniformly in a mass ratio of 6:1 to obtain a uniform mixture of water and ethanol, adjust the pH value to 3 with hydrochloric acid, place it in a magnetic stirrer, and add tetraethyl orthosilicate so that the mass fraction is 1.5%. Set the stirring temperature to 70°C, the stirring speed to 200 rpm, and the stirring time to 50 min.

[0071] (2) Continue to add polyallylamine, so that the mass fraction of polyallylamine is 1.5%, continue to stir for 30 min, and then a silanol / polyallylamine modified solution is obtained.

[0072] (3) Prepare a 0.3% piperazine aqueous phase solution (solvent: deionized water) and a 0.2% trimesoyl chloride oil phase solution (solvent: Isopar L).

[0073] Step (4) refer to Example 1.

[0074] Example 6

[0075] The preparation method of the nanofiltration membrane of the present example is as follows:

[0076] (1) Mix water and ethanol uniformly at a mass ratio of 10:1 to obtain a uniform mixture of water and ethanol, adjust the pH value to 3 with hydrochloric acid, place it in a magnetic stirrer, and add tetraethyl orthosilicate so that the mass fraction is 4%. Set the stirring temperature to 50°C and the stirring speed to 300 rpm, and stir for 1 h.

[0077] (2) Continue to add polyallylamine so that the mass fraction of polyallylamine is 0.5%, and after continuing to stir for 30 min, a silanol / polyallylamine modified solution is obtained.

[0078] (3) Prepare a 0.15% piperazine + 0.3% m-phenylenediamine aqueous phase solution (solvent: deionized water) and a 0.2% trimesoyl chloride oil phase solution (solvent: Isopar L).

[0079] Step (4) refer to Example 1.

[0080] Example 7

[0081] The preparation method of the nanofiltration membrane of the present example is as follows:

[0082] (1) Mix water and ethanol uniformly at a mass ratio of 5:1 to obtain a uniform mixture of water and ethanol, adjust the pH value to 3 with hydrochloric acid, place it in a magnetic stirrer, and add tetraethyl orthosilicate so that the mass fraction is 3%. Set the stirring temperature to 70°C and the stirring speed to 200 rpm, and stir for 30 min.

[0083] (2) Continue to add polyallylamine so that the mass fraction of polyallylamine is 0.5%, and after continuing to stir for 30 min, a silanol / polyallylamine modified solution is obtained.

[0084] (3) Prepare a 0.15% piperazine + 0.3% m-phenylenediamine aqueous phase solution (solvent: deionized water) and a 0.2% trimesoyl chloride oil phase solution (solvent: Isopar L).

[0085] Step (4) refer to Example 1.

[0086] Example 8

[0087] The preparation method of the nanofiltration membrane of the present example is as follows:

[0088] (1) Water and ethanol were uniformly mixed in a mass ratio of 4:1 to obtain a uniform mixture of water and ethanol. The pH value was adjusted to 3 with hydrochloric acid, and the mixture was placed in a magnetic stirrer. Ammonia propyl triethoxysilane was added to make the mass fraction 3%. The stirring temperature was set to 50°C, the stirring speed was 200 rpm, and the stirring time was 1 h.

[0089] (2) Polyethyleneimine was continuously added to make the mass fraction of polyethyleneimine 0.5%. After continuous stirring for 30 min, a silanol / polyethyleneimine modified solution was obtained.

[0090] Steps (3)-(4) are the same as in Example 1.

[0091] Example 9

[0092] The preparation method of the nanofiltration membrane of this example is as follows:

[0093] (1) Water and ethanol were uniformly mixed in a mass ratio of 4:1 to obtain a uniform mixture of water and ethanol. The pH value was adjusted to 3 with hydrochloric acid, and the mixture was placed in a magnetic stirrer. Ammonia propyl triethoxysilane was added to make the mass fraction 3%. The stirring temperature was set to 60°C, the stirring speed was 200 rpm, and the stirring time was 1.5 h.

[0094] (2) Polyethyleneimine was continuously added to make the mass fraction of polyethyleneimine 0.5%. After continuous stirring for 30 min, a silanol / polyethyleneimine modified solution was obtained.

[0095] (3) A water phase solution of piperazine with a mass fraction of 0.3% and ethylenediamine with a mass fraction of 0.2% (solvent: deionized water) and an oil phase solution of trimesoyl chloride with a mass fraction of 0.15% (solvent: Isopar L) were prepared.

[0096] Step (4) is described in Example 1.

[0097] Comparative Example 1

[0098] This comparative example is based on Example 1, but does not have a silanol / polyethyleneimine network intermediate layer on the polysulfone base film. That is, the preparation method of the nanofiltration membrane of this comparative example is as follows:

[0099] (1) A water phase solution of piperazine with a mass fraction of 0.5% (solvent: deionized water) and an oil phase solution of trimesoyl chloride with a mass fraction of 0.2% (solvent: Isopar L) were prepared.

[0100] (2) The water phase solution was coated on the polysulfone base film and the excess solution was removed after 60 s. The film was dried in air, and then the oil phase solution was coated on the dried support film. The excess solution was removed after 20 s, and the film was placed in an oven at 100°C for 5 min.

[0101] Comparative Example 2

[0102] This comparative example is based on Example 1, and step (2) is omitted, i.e. no amine polymer is added in the modification solution. The remaining steps and preparation conditions are the same as those of Example 1.

[0103] Comparative Example 3

[0104] This comparative example is based on Example 1, and no tetraethyl orthosilicate is added in step (1), i.e. only the amine polymer is added in the modification solution. The remaining steps and preparation conditions are the same as those of Example 1.

[0105] Comparative Example 4

[0106] This comparative example is based on Example 1, and no hydrochloric acid is used to adjust the pH value to 3 in step (1), and the stirring is performed at 50°C under neutral conditions at a speed of 200 rpm for 1 h. The remaining steps and preparation conditions are the same as those of Example 1.

[0107] Comparative Example 5

[0108] This comparative example is based on Example 1, and the stirring speed is increased to 800 rpm in step (1) for 1 h. The remaining steps and preparation conditions are the same as those of Example 1.

[0109] The membranes prepared in Examples 1-5 and Comparative Examples 1-3 above are tested by the following method:

[0110] The rejection rate is defined as the difference between the concentrations of the corresponding ions in the concentrated water and the product water divided by the original concentration of the concentrated water; and the water flux is defined as the water volume per unit area of the composite separation membrane per unit time during the above test, and the unit is L·m -2 h -1 (LMH). Each data point is obtained by averaging 3 samples.

[0111] (1) Test Condition 1:

[0112] Water sample: 2000 ppm LiCl aqueous solution, pH 6.5-7.5.

[0113] The test pressure is 0.5 MPa, the concentrated water flow is 1.0 GPM, and the ambient temperature is 25°C.

[0114] (2) Test Condition 2:

[0115] Water sample: 2000 ppm MgCl2 aqueous solution, pH 6.5-7.5.

[0116] The test pressure is 0.5 MPa, the concentrated water flow is 1.0 GPM, and the ambient temperature is 25°C.

[0117] The test results of each nanofiltration membrane are as follows:

[0118]

[0119]

[0120] From the above table, it can be seen that:

[0121] The nanofiltration membranes of Examples 1-9 have significantly improved magnesium ion rejection and have not significantly decreased water flux compared to Comparative Example 1. This is mainly because the silanol intermediate layer repairs the defects of the surface polyamide active separation layer, and the amine polymer contained in the intermediate layer adjusts the membrane potential, thereby improving the rejection of divalent or multivalent cations. The nanofiltration membranes of Examples 1-9 have a certain degree of decrease in lithium ion rejection compared to Comparative Example 1, but the water flux is higher than that of each comparative example. This is mainly because the silanol three-dimensional network intermediate layer on the substrate material increases the hydrophilicity of the nanofiltration membrane, which is beneficial to the formation of a loose separation functional layer, and at the same time avoids the phenomenon of polyamide layer growing into the pores of the substrate material and blocking the pores of the substrate material, thereby reducing the mass transfer resistance and improving the water flux. The modification solution of Comparative Example 2 does not add amine polymer, which also leads to a decrease in the rejection of magnesium ions and an increase in the rejection of lithium ions. At the same time, the performance of the nanofiltration membrane is unstable during use, and the functional separation layer structure on the surface of the nanofiltration membrane is severely damaged after 12 hours of operation. This shows that if a certain amount of amine polymer is not added to the modification solution, only the silanol precursor hydrolysis and condensation network intermediate layer is used to modify the substrate material, and the intermediate layer is easy to separate from the surface polyamide active separation layer. The modification solution of Comparative Example 3 only contains amine and does not contain silanol, which leads to a decrease in the rejection of magnesium ions and an increase in the rejection of lithium ions, and a decrease in water flux. This is mainly because when the amine polymer modifies the substrate material, although the positive charge is beneficial to the rejection of divalent or multivalent cations, the amine polymer has poor repair effect on the filter hole defects of the surface polyamide active separation layer, and the overall rejection of magnesium ions is still low. Moreover, only amine polymer cannot well improve the hydrophilicity of the membrane, so the water flux of the membrane to lithium salt is reduced. In Comparative Example 4, the modification solution is prepared under neutral conditions, at which most of the silanol precursors cannot undergo hydrolysis and recondensation processes, and it is difficult to produce a silanol / amine polymer three-dimensional network intermediate layer with complete morphology and structure, which has a similar modification effect on the nanofiltration membrane as Comparative Example 3. In Comparative Example 5, although the conditions for preparing the modification solution meet the requirements for silanol hydrolysis and recondensation, it is still difficult to form a silanol / amine polymer three-dimensional network intermediate layer with complete morphology and structure due to the excessive stirring speed and strong shear effect. Although it can increase the surface roughness of the surface polyamide active separation layer to a certain extent, the improvement effect on the nanofiltration membrane is still not as good as that of Examples 1-9.

[0122] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for producing a nanofiltration membrane having a silanol three-dimensional network interlayer, characterized by, The preparation method comprises the following steps: S1, pretreatment a silanol / amine polymer modification liquid is coated on a base film material, and excess modification liquid is removed to form a silanol three-dimensional network intermediate layer on the base film material; the preparation method of the silanol / amine polymer modification liquid is as follows: a silanol precursor is dissolved in a mixed liquid of water and ethanol, the pH is adjusted to be acidic, heating and stirring are performed to make the silanol precursor hydrolyze and re-condense to form a silanol network structure, and then at least one amine polymer is added to mix and interweave with the silanol network structure to obtain the silanol / amine polymer modification liquid; the silanol precursor is one or more than two combinations of tetraethyl orthosilicate, aminopropyl triethoxysilane and silicon tetrachloride, and the amine polymer is at least one of polyvinylamine, polyallylamine, polyethyleneimine, polyacrylamide and polyamidoamine; S2, interfacial polymerization an aqueous solution containing an amine monomer and an oil phase solution containing an acid chloride monomer are coated on the base film material with the silanol three-dimensional network intermediate layer in sequence, and heat treatment is performed to complete the interfacial polymerization and generate a polyamide crosslinked network layer, which together with the silanol three-dimensional network intermediate layer forms a functional separation layer of a nanofiltration membrane.

2. The production method according to claim 1, characterized by, In S1, the mass fraction of the silanol precursor in the modification liquid is 0.5%-5%.

3. The preparation method according to claim 1, characterized in that, In S1, the mixed mass ratio of water and ethanol in the mixed liquid of water and ethanol is 10-2:

1.

4. The method of claim 1, wherein, In S1, during the preparation process of the silanol / amine polymer modification liquid: the pH is adjusted to be 2-6; specifically, the pH is adjusted to be acidic by adding an inorganic acid; the inorganic acid is at least one of hydrochloric acid, sulfuric acid, nitric acid, boric acid and phosphoric acid; the heating temperature is 35-75°C; the stirring time is 30 min-90 min, and the stirring speed is 200 rpm-500 rpm.

5. The preparation method according to claim 1, characterized in that, In S1, the mass fraction of the amine polymer in the modification liquid is 0.5%-3%.

6. The preparation method according to claim 5, characterized in that, After the amine polymer is added, the amine polymer is mixed and interwoven with the silanol network structure by continuing to stir to obtain the silanol / amine polymer modification liquid; the time for continuing to stir is 15-50 min.

7. The preparation method according to claim 1, characterized in that, In S2, in the aqueous solution for the interfacial polymerization, the amine monomer is one or more than two combinations of piperazine, diamino dipropylamine, ethylenediamine, diethylenetriamine, 2,5-dimethylpiperazine, m-phenylenediamine, p-phenylenediamine and o-phenylenediamine, and the mass fraction of the amine monomer in the aqueous solution is 0.1%-5%; in the oil phase solution for the interfacial polymerization, the acid chloride monomer is one or more than two combinations of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride and isophthaloyl chloride, and the mass fraction of the acid chloride monomer in the oil phase solution is 0.05%-3%.

8. The preparation method according to claim 1, characterized in that, The process in S1 is: dissolving at least one silanol precursor of tetraethyl orthosilicate, aminopropyl triethoxysilane and silicon tetrachloride in a solution of water and ethanol with a mass ratio of 10-2:1, adding acid to adjust pH to 3-5, heating to 35-75°C, stirring at 200-500 rpm for 30 min-90 min, hydrolyzing and recondensing the silanol precursor into a silanol network structure under acidic conditions, then adding at least one amine polymer of polyvinylamine, polyallylamine, polyethyleneimine, polyacrylamide and polyamidoamine, continuing to stir for 15-50 min, mixing and interlacing the amine polymer with the silanol network structure to obtain a modified liquid; In the modified liquid, the mass concentration of the silanol precursor is 0.5%-5%, and the mass concentration of the amine polymer is 0.5%-3%; the modified liquid is coated on the base film material, and after standing for 1-15 min, the excess modified liquid is removed, dried, and a silanol three-dimensional network intermediate layer is formed on the base film material; The process in S2 is: coating an aqueous solution on the base film material with a silanol three-dimensional network intermediate layer, removing the excess aqueous solution after 30-90 s, blowing dry or air drying, then coating an oil phase solution on the dried base film material, removing the excess oil phase solution after 20-40 s, and then transferring to an oven for heat treatment at 40°C-140°C for 2-10 min; The aqueous solution is formed by dissolving at least one amine monomer of piperazine, diamino dipropylamine, ethylenediamine, diethylenetriamine, 2,5-dimethylpiperazine, m-phenylenediamine, p-phenylenediamine and o-phenylenediamine in water to form an aqueous solution with a mass concentration of 0.1%-5%; the aqueous solution is added with an acid absorbent with a mass concentration of 0-3%; the oil phase solution is formed by dissolving at least one acyl chloride monomer of trimesoyl chloride, terephthaloyl chloride, phthaloyl chloride and isophthaloyl chloride in an oil agent to form an oil phase solution with a mass concentration of 0.05%-3%; the oil agent is one or a mixture of several of IsoparL, IsoparG, IsoparM, IsoparE, n-hexane and cyclohexane.

9. A nanofiltration membrane with a silanol three-dimensional network intermediate layer, which is prepared by the method of any one of claims 1-8.

Images