A nanofiltration membrane and a method for its preparation

Abstract

The embodiment of the present application provides a kind of nanofiltration membrane and its preparation method.The nanofiltration membrane provided by the embodiment of the present application includes base film, and the separation layer is arranged on the base film, and the separation layer includes the polymer formed based on tobramycin.Thus, tobramycin can provide a large number of amino groups and hydroxyl groups for nanofiltration membrane, electrostatic effect is generated by amino group, lithium ions and other ions are selectively separated, and other ions can be effectively intercepted, to improve the selectivity of nanofiltration membrane.Meanwhile, the amino groups and hydroxyl groups provided by tobramycin control the relatively loose separation layer formed by nanofiltration membrane, can improve the permeability of nanofiltration membrane, and effectively improve the processing efficiency of nanofiltration membrane.

Description

Technical Field

[0001] This invention relates to the field of separation technology, and in particular to a nanofiltration membrane and a method for preparing the nanofiltration membrane. Background Technology

[0002] Lithium is an important energy metal and is currently widely used in energy storage technologies such as batteries. In my country, lithium resources typically exist in solution form, which usually contains lithium ions as well as other ions. To extract lithium, it is necessary to separate lithium ions from the other ions.

[0003] In existing technologies, lithium ions can be separated from other ions through selective ion separation methods such as ultrafiltration, nanofiltration, and reverse osmosis. However, existing selective ion separation methods typically have poor selectivity and may not effectively retain other ions. Furthermore, they may suffer from poor permeability, leading to low processing efficiency. Summary of the Invention

[0004] The present invention provides a nanofiltration membrane and a method for preparing the nanofiltration membrane, so as to improve the selectivity of the nanofiltration membrane for lithium ions and maintain good permeation performance.

[0005] This invention discloses a nanofiltration membrane, which includes a base membrane and a separation layer disposed on the base membrane, the separation layer comprising a polymer based on tobramycin.

[0006] Optionally, the separation layer specifically comprises a polymer based on tobramycin, polyamines, and acyl chloride compounds.

[0007] Optionally, the nanofiltration membrane surface is positively charged.

[0008] Optionally, the nanofiltration membrane is used to separate polyvalent positive ions and lithium ions in a lithium-containing solution.

[0009] Optionally, the nanofiltration membrane has a lithium ion rejection rate of less than -30% and a polyvalent positive ion rejection rate of greater than 97%.

[0010] Optionally, the water flux of the nanofiltration membrane is greater than 200 LMH.

[0011] This invention also provides a method for preparing a nanofiltration membrane, the method comprising:

[0012] A first aqueous phase solution and an oil phase solution are disposed on the surface of the base film; wherein, the first aqueous phase solution includes tobramycin;

[0013] The first aqueous solution and the oil solution polymerize to form a separation layer disposed on the base membrane; the separation layer comprises a polymer based on tobramycin.

[0014] Optionally, the step of setting the first aqueous solution and the oil solution on the surface of the base film includes:

[0015] A first aqueous solution is disposed on the surface of the base film;

[0016] After the first aqueous phase solution is uniformly distributed on the surface of the base film, the oil phase solution is then placed on the base film.

[0017] Optionally, the first aqueous solution further includes a polyamine, and the oil phase solution includes an acyl chloride compound;

[0018] The step of polymerizing the first aqueous solution with the oil solution to form a separation layer on the base film includes:

[0019] The polyamine and tobramycin in the first aqueous solution polymerize with the acyl chloride compound in the oil solution to form a separation layer disposed on the base film. The separation layer comprises a polymer based on tobramycin, polyamine, and acyl chloride compound.

[0020] Optionally, the method includes:

[0021] A second aqueous solution is disposed on the surface of the separation layer to form a composite separation layer; wherein the second aqueous solution includes tobramycin.

[0022] Optionally, the mass fraction of tobramycin in the first aqueous solution is 0.02%-1%, and / or the mass fraction of tobramycin in the second aqueous solution is 0.02%-1%.

[0023] Optionally, the mass fraction of the polyamine in the first aqueous phase solution is 0.02%-1%, and / or the mass fraction of the acyl chloride compound in the oil phase solution is 0.02%-3%.

[0024] Optionally, the first aqueous solution further includes an acid-absorbing agent, and / or the second aqueous solution further includes an acid-absorbing agent;

[0025] The acid absorbent includes one or more of sodium hydroxide, triethylamine, potassium phosphate, sodium carbonate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, and potassium dihydrogen phosphate.

[0026] Optionally, the oil phase solution further includes an oily solvent, which includes one or more of n-heptane, n-hexane, and isoparaffin solvents.

[0027] The embodiments of the present invention have the following advantages:

[0028] The nanofiltration membrane provided by the embodiments of the present invention includes a base membrane and a separation layer disposed on the base membrane, the separation layer comprising a polymer based on tobramycin. Thus, tobramycin can provide the nanofiltration membrane with a large number of amino and hydroxyl groups. The amino groups generate electrostatic interactions, selectively separating lithium ions from other ions and effectively retaining other ions, thereby improving the selectivity of the nanofiltration membrane. Simultaneously, the amino and hydroxyl groups provided by tobramycin control the formation of a relatively loose separation layer in the nanofiltration membrane, improving the permeability of the nanofiltration membrane and effectively increasing its treatment efficiency. Attached Figure Description

[0029] Figure 1 This is a SEM characterization image of the nanofiltration membrane surface provided in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the water contact angle test on the surface of a nanofiltration membrane provided in an embodiment of the present invention. Detailed Implementation

[0031] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0032] This invention discloses a nanofiltration membrane, which includes a base membrane and a separation layer disposed on the base membrane, the separation layer comprising a polymer based on tobramycin.

[0033] In this embodiment of the invention, the nanofiltration membrane may include a base membrane and a separation layer. The base membrane typically provides mechanical support for the separation layer. The base membrane is usually selected from materials with a porous structure and chemical stability. Its porous structure allows water and other solutes to pass through while supporting the separation layer. Its chemical stability provides the nanofiltration membrane with a long service life.

[0034] Generally, the base membrane can be made of materials such as polysulfone, polyethersulfone, polypropylene, and polyester. Among them, polysulfone and polyethersulfone have suitable pore sizes, good mechanical strength, and chemical stability for nanofiltration membranes, making them more suitable as the base membrane for the nanofiltration membrane in the embodiments of this invention.

[0035] In this embodiment of the invention, the separation layer can be used to selectively separate lithium ions based on pore size and electrostatic interaction. The pore size of the separation layer can be at the nanometer level, allowing the nanofiltration membrane to isolate solutes with excessively large molecular weights. Simultaneously, the separation layer comprises a polymer based on tobramycin, which provides a large number of amino groups to the separation layer. These amino groups can hydrolyze in water, causing the nanofiltration membrane to become charged, thereby generating electrostatic interaction. This electrostatic interaction can exert different repulsive forces on ions with different valences. High-valence ions experience greater repulsion and are thus retained by the separation layer, while low-valence ions, such as lithium ions, experience less repulsion and can pass through the separation layer normally. Therefore, lithium ions can be separated from other ions, allowing for the selective screening of lithium ions.

[0036] Meanwhile, tobramycin provides a large number of amino and hydroxyl groups during the preparation of nanofiltration membranes, exhibiting good hydrophilicity. In the interfacial polymerization method for nanofiltration membrane preparation, compounds in the aqueous and oil phase solutions react at the interface to form a polymer, thus creating a separation layer. At this point, the amino and hydroxyl groups of tobramycin attract compounds in the aqueous phase solution through intermolecular forces, reducing the migration rate of these compounds to the interface. This makes the interfacial polymerization process for nanofiltration membrane preparation relatively mild, resulting in a relatively loose separation layer. This allows the solution to pass through the nanofiltration membrane more easily, maintaining its good permeability and improving the efficiency of lithium ion separation in solution.

[0037] In one embodiment of the present invention, the separation layer specifically comprises a polymer based on tobramycin, polyamines, and acyl chloride compounds.

[0038] Specifically, the separation layer may comprise a polymer based on tobramycin, polyamines, and acyl chloride compounds. The polyamines can react with the acyl chloride compounds to form polymers containing amino groups, enabling the separation layer to generate electrostatic interactions and achieve the separation of ions with different valences. By further adding tobramycin to participate in the reaction between the polyamines and acyl chloride compounds, more amino and hydroxyl groups can be introduced into the polymer, thereby further improving the separation layer's retention effect on high-valence ions and enhancing the selective separation of low-valence lithium ions.

[0039] As a specific example of the present invention, polyamines may include polyetherimides, piperazines, polyethyleneimine, m-phenylenediamine, and p-phenylenediamine, etc. Acyl chloride compounds may include terephthaloyl chloride, isophthaloyl chloride, and trimesoyl chloride, etc.

[0040] In one embodiment of the present invention, the nanofiltration membrane surface is positively charged.

[0041] Generally, nanofiltration membranes are typically negatively charged. Negatively charged nanofiltration membranes can selectively separate lithium ions by attracting positively charged lithium ions and repelling negatively charged ions. However, solutions containing lithium ions in nature often also contain other positively charged ions. These ions are usually attracted to negatively charged nanofiltration membranes, resulting in a lower rejection rate for other positively charged ions.

[0042] The main objective of separating lithium ions from lithium-containing solutions is to separate lithium ions from other positively charged ions, preventing these ions from interfering with subsequent lithium ion extraction processes. Therefore, in this embodiment of the invention, tobramycin is added to ensure that during the polymerization of the polyamine and the acyl chloride compound, the acyl chloride groups in the acyl chloride compound can fully react with the polyamine and tobramycin, resulting in the nanofiltration membrane surface primarily containing amino groups and thus exhibiting a positive charge.

[0043] Positively charged nanofiltration membranes can repel positively valent ions to some extent, but the repulsive force varies depending on the valence of the positive ions. Lithium ions, due to their lower valence, experience less repulsion and can pass through the nanofiltration membrane normally. Other positively valent ions, however, experience greater repulsion than lithium ions, causing them to be retained by the nanofiltration membrane, thus effectively achieving selective separation of lithium ions.

[0044] In one embodiment of the present invention, the nanofiltration membrane is used to separate polyvalent positive ions and lithium ions in a lithium-containing solution.

[0045] Specifically, the embodiments of the present invention can be used to separate lithium ions in lithium-containing solutions. Lithium-containing solutions typically contain lithium ions as well as multivalent positive ions. By using a nanofiltration membrane to generate different repulsive forces on positive ions of different valences, lithium ions in the lithium-containing solution can pass through the nanofiltration membrane normally, while multivalent positive ions are retained, thereby achieving selective separation of lithium ions.

[0046] As a specific example of the present invention, the lithium-containing solution can be brine from a salt lake. Salt lake brine is a major source of lithium resources. Salt lake brines mainly contain large amounts of magnesium and lithium ions, with the magnesium ion content often being much higher than the lithium ion content. In most salt lake brines, the magnesium / lithium mass ratio is higher than 40. Because magnesium and lithium ions have similar hydration radii, their behavior in aqueous solutions is similar, making them difficult to separate simply by physical methods. Furthermore, the similar chemical properties of magnesium and lithium ions also make them difficult to separate simply through chemical reactions.

[0047] In this embodiment of the invention, by setting the nanofiltration membrane to generate different repulsive forces for positive ions with different valences, lithium ions in the salt lake brine can pass through the nanofiltration membrane normally, while magnesium ions are retained. Thus, the magnesium ions present in large quantities in the salt lake brine can be effectively separated from lithium ions, avoiding the impact of magnesium ions on the subsequent extraction of lithium ions.

[0048] In one embodiment of the present invention, the nanofiltration membrane has a lithium ion rejection rate of less than -30% and a polyvalent positive ion rejection rate of greater than 97%.

[0049] In this embodiment of the invention, the nanofiltration membrane generates a repulsive force through electrostatic interaction, allowing lithium ions to pass through while retaining polyvalent positive ions. By incorporating a tobramycin-based polymer into the separation layer of the nanofiltration membrane, which primarily contains amino groups, the surface of the nanofiltration membrane becomes positively charged through the hydrolysis of these amino groups in water. This positively charged nanofiltration membrane effectively retains polyvalent positive ions, achieving a retention rate greater than 97%. Simultaneously, the nanofiltration membrane in this embodiment exhibits a moderate amount of positive charge on its surface, allowing low-valent lithium ions to pass through normally, with a retention rate of less than -30%. Therefore, the nanofiltration membrane in this embodiment of the invention demonstrates high selectivity for lithium ions and effectively separates lithium ions from polyvalent positive ions.

[0050] In one embodiment of the present invention, the water flux of the nanofiltration membrane is greater than 200 LMH.

[0051] Specifically, in the preparation of nanofiltration membranes, tobramycin can provide a large number of amino and hydroxyl groups, exhibiting good hydrophilicity. In the interfacial polymerization method for nanofiltration membrane preparation, compounds in the aqueous and oil phase solutions react at the interface to form a polymer, thus creating a separation layer. At this point, the amino and hydroxyl groups of tobramycin can attract compounds in the aqueous phase solution through intermolecular forces, reducing the migration rate of these compounds to the interface. This makes the interfacial polymerization process for nanofiltration membrane preparation relatively mild, resulting in a relatively loose separation layer. This allows the solution to pass through the nanofiltration membrane more easily, maintaining its good permeability. The water flux of the nanofiltration membrane is greater than 200 LMH, enabling it to process more solution per unit time and improving the efficiency of lithium ion separation.

[0052] This invention also provides a method for preparing a nanofiltration membrane, the method comprising:

[0053] Step 101: A first aqueous phase solution and an oil phase solution are disposed on the surface of the base film; wherein, the first aqueous phase solution includes tobramycin;

[0054] Step 102, the first aqueous solution and the oil solution polymerize to form a separation layer disposed on the base membrane; the separation layer comprises a polymer based on tobramycin.

[0055] In this embodiment of the invention, a first aqueous solution and an oil phase solution can be disposed on the surface of the base film. The compounds in the first aqueous solution and the oil phase solution can undergo a polymerization reaction at the interface between the aqueous and oil phases to form a polymer.

[0056] In this embodiment of the invention, the first aqueous solution includes tobramycin. During the polymerization reaction of the compounds in the first aqueous solution and the oil solution, tobramycin can be further introduced so that the polymer in the separation layer mainly contains amino groups. These amino groups can hydrolyze in water, causing the nanofiltration membrane to become charged, thus generating electrostatic effects. These electrostatic effects can exert different repulsive forces on ions of different valences. High-valence ions experience greater repulsive forces and are thus retained by the separation layer, while low-valence ions, such as lithium ions, experience less repulsive forces and can pass through the separation layer normally. Therefore, lithium ions can be separated from other ions, allowing for the selective screening of lithium ions.

[0057] Meanwhile, tobramycin provides a large number of amino and hydroxyl groups during the preparation of nanofiltration membranes, exhibiting good hydrophilicity. In both the aqueous and oil phases, the compound can undergo polymerization at the interface between the aqueous and oil phases. During polymer formation, the amino and hydroxyl groups of tobramycin attract the compound in the aqueous phase through intermolecular forces, reducing the migration rate of the compound from the aqueous phase to the interface. This makes the interfacial polymerization process for nanofiltration membrane preparation relatively mild, forming a relatively loose separation layer that allows the solution to pass through the nanofiltration membrane more easily, maintaining its good permeability and improving the efficiency of lithium ion separation in solution.

[0058] In one embodiment of the present invention, the step of setting a first aqueous phase solution and an oil phase solution on the surface of the base film includes:

[0059] S11, A first aqueous solution is disposed on the surface of the base film;

[0060] S12, after the first aqueous phase solution is uniformly distributed on the surface of the base film, the oil phase solution is placed on the base film.

[0061] In practice, a first aqueous solution can be first placed on the base membrane surface and allowed to stand for a period of time. The first aqueous solution can then spread on the base membrane surface. After the first aqueous solution has been evenly distributed on the base membrane surface, the oil phase solution is then placed on the base membrane. This allows the two-phase interface formed by the aqueous and oil phase solutions to cover the base membrane as much as possible, thereby enabling a better separation layer to form on the base membrane surface.

[0062] In order to ensure that the separation layer is evenly distributed on the surface of the base film and has a suitable thickness, rollers can be used to assist in the stretching process during the preparation of the first aqueous solution and oil solution, and to remove excess first aqueous solution and oil solution, so that the first aqueous solution and oil solution are evenly distributed on the surface of the base film.

[0063] As a specific example of the present invention, a first aqueous solution can be first added to the surface of the base film. After standing for 30 seconds to 10 minutes, the excess first aqueous solution is poured off, and a rubber roller is used to further remove excess first aqueous solution from the surface of the base film, so that the first aqueous solution is evenly distributed on the surface of the base film without excess water overflow. Subsequently, an oil phase solution is placed on the base film. At this time, the compounds in the aqueous solution and tobramycin can react with the compounds in the oil phase solution. After the reaction lasts for 30 seconds to 10 minutes, the excess oil phase solution is poured off, and a rubber roller is used to remove excess oil phase solution from the surface of the base film.

[0064] In one embodiment of the present invention, the first aqueous phase solution further includes a polyamine, and the oil phase solution includes an acyl chloride compound.

[0065] The step of polymerizing the first aqueous solution with the oil solution to form a separation layer on the base film includes:

[0066] S21, the polyamine and tobramycin in the first aqueous solution polymerize with the acyl chloride compound in the oil solution to form a separation layer disposed on the base film, the separation layer comprising a polymer based on tobramycin, polyamine and acyl chloride compound.

[0067] The first aqueous phase solution also includes a polyamine, and the oil phase solution includes an acyl chloride compound. The polyamine in the first aqueous phase solution can react with the acyl chloride compound in the oil phase solution to form a polymer containing amino groups, which allows the separation layer to generate electrostatic interactions, achieving the separation of ions with different valences. By further adding tobramycin to the first aqueous phase solution to participate in the reaction between the polyamine and the acyl chloride compound, more amino and hydroxyl groups can be introduced into the polymer, thereby further improving the retention effect of the separation layer on high-valence ions and enhancing the selective separation effect on low-valence lithium ions.

[0068] As a specific example of the present invention, polyamines may include polyetherimides, piperazines, polyethyleneimine, m-phenylenediamine, and p-phenylenediamine, etc. Acyl chloride compounds may include terephthaloyl chloride, isophthaloyl chloride, and trimesoyl chloride, etc.

[0069] In one embodiment of the present invention, the method includes:

[0070] S31, a second aqueous solution is disposed on the surface of the separation layer to form a composite separation layer; wherein, the second aqueous solution includes tobramycin.

[0071] In this embodiment of the invention, to ensure a positively charged nanofiltration membrane surface, a composite separation layer can be formed using a multiple interfacial polymerization method, ensuring complete reaction of the acyl chloride groups on the nanofiltration membrane surface. Consequently, a second aqueous solution can be placed on the surface of the separation layer. This second aqueous solution includes tobramycin, which, through the amino and hydroxyl groups provided by tobramycin, completely reacts the acyl chloride groups in the oil phase solution, resulting in a composite separation layer surface containing a large number of amino and hydroxyl groups provided by tobramycin, further improving the overall water flux of the nanofiltration membrane.

[0072] Optionally, the first aqueous solution and the oil solution polymerize to form a separation layer on the base membrane, and a second aqueous solution is further deposited on the surface of the separation layer to form a composite separation layer. At this point, the composite separation layer is initially formed, but it is not cured on the surface of the base membrane, and the solvents in the first aqueous solution, oil solution, and second aqueous solution have not been removed from the surface of the base membrane. In this case, the base membrane can be placed in an oven at 50℃-120℃ for heat treatment to cure the composite separation layer and remove excess solvent. After 3-30 minutes, it is taken out to obtain the prepared nanofiltration membrane.

[0073] In one embodiment of the present invention, the mass fraction of tobramycin in the first aqueous solution is 0.02%-1%, and / or the mass fraction of tobramycin in the second aqueous solution is 0.02%-1%.

[0074] In this embodiment of the invention, tobramycin requires an appropriate amount. If the amount added is too small, unreacted acyl chloride groups may remain in the separation layer, resulting in a negative charge on the nanofiltration membrane and preventing the selective separation of lithium ions through electrostatic interaction. Conversely, if the amount added is too large, the electrostatic interaction on the nanofiltration membrane surface may be too strong, not only retaining polyvalent positive ions but also lithium ions, thus failing to achieve selective lithium ion separation. Therefore, the mass fraction of tobramycin in the first aqueous phase solution can be set to 0.02%-1%, and / or the mass fraction of tobramycin in the second aqueous phase solution can be set to 0.02%-1%. At these mass fractions, tobramycin provides an appropriate amount of amino and hydroxyl groups, enabling the selective separation of lithium ions.

[0075] In one embodiment of the present invention, the mass fraction of the polyamine in the first aqueous phase solution is 0.02%-1%, and / or the mass fraction of the acyl chloride compound in the oil phase solution is 0.02%-3%.

[0076] Specifically, the mass fraction of the polyamine in the first aqueous solution and the mass fraction of the acyl chloride compound in the oil solution can affect the thickness of the prepared separation layer. To enable the nanofiltration membrane to selectively separate lithium ions without affecting the water flux due to an excessively thick separation layer, the mass fraction of the polyamine in the first aqueous solution can be set to 0.02%-1%, and the mass fraction of the acyl chloride compound in the oil solution to 0.02%-3%. In this case, the resulting separation layer can have a suitable thickness.

[0077] In one embodiment of the present invention, the first aqueous solution further includes an acid-absorbing agent, and / or the second aqueous solution further includes an acid-absorbing agent;

[0078] The acid absorbent includes one or more of sodium hydroxide, triethylamine, potassium phosphate, sodium carbonate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, and potassium dihydrogen phosphate.

[0079] Specifically, during the reaction between the polyamine and tobramycin in the first aqueous phase solution and the acyl chloride compound in the oil phase solution, acidic byproducts may be generated. These acidic byproducts may affect the reaction process, preventing the separation layer from forming properly. Therefore, an acid-scavenging agent can be added to the first and / or second aqueous phase solutions to neutralize the acidic byproducts during the reaction, ensuring the proper formation of the separation layer.

[0080] In specific implementations, the acid absorbent can be one or more alkaline compounds such as sodium hydroxide, triethylamine, potassium phosphate, sodium carbonate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, and potassium dihydrogen phosphate.

[0081] In one embodiment of the present invention, the oil phase solution further includes an oily solvent, which includes one or more of n-heptane, n-hexane, and isoparaffin solvents.

[0082] Specifically, the oil phase solution also includes an oily solvent. To promote the interfacial polymerization reaction, one or more solvents with good solubility in acyl chloride compounds and immiscibility with water, such as n-heptane, n-hexane, and isoparaffin solvents (e.g., ISOPARG), can be selected as the oily solvent.

[0083] To enable those skilled in the art to better understand the present invention, the following describes the preparation method of the nanofiltration membrane of the present invention through several specific embodiments.

[0084] Example 1

[0085] 1) Prepare a first aqueous phase solution containing polyetherimide (0.5% by mass), tobramycin (1% by mass), and sodium hydroxide (1% by mass). Prepare a 0.2% (w / w) solution of trimesoyl chloride in n-heptane as the oil phase solution. Prepare a second aqueous phase solution containing tobramycin (1% by mass) and sodium hydroxide (0.5% by mass).

[0086] 2) Pour the first aqueous phase solution onto the base film surface, let it stand for 1 minute, then pour it off, and use a rubber roller to remove excess first aqueous phase solution from the base film surface;

[0087] 3) Pour the organic phase solution onto the base film surface, react for 1 minute, then pour off the excess oil phase solution and use a rubber roller to remove the excess oil phase solution from the base film surface;

[0088] 4) Pour the second aqueous phase solution onto the surface of the base film, react for 1 minute, and then pour off the excess second aqueous phase solution;

[0089] 5) Place the base membrane in an oven at 80°C for heat treatment. After 5 minutes, remove it to obtain the prepared nanofiltration membrane.

[0090] Example 2

[0091] 1) Prepare a first aqueous phase solution containing polyetherimide (0.5% by mass), tobramycin (0.6% by mass), and triethylamine (1% by mass). Prepare a 0.2% (w / w) solution of pyromellitic trimethylol chloride in n-heptane as the oil phase solution. Prepare a second aqueous phase solution containing tobramycin (0.6% by mass) and triethylamine (1% by mass).

[0092] 2) Pour the first aqueous phase solution onto the base film surface, let it stand for 1 minute, then pour it off, and use a rubber roller to remove excess first aqueous phase solution from the base film surface;

[0093] 3) Pour the organic phase solution onto the base film surface, react for 1 minute, then pour off the excess oil phase solution and use a rubber roller to remove the excess oil phase solution from the base film surface;

[0094] 4) Pour the second aqueous solution onto the surface of the base film, react for 30 seconds, and then pour off the excess second aqueous solution;

[0095] 5) Place the base membrane in an oven at 80°C for heat treatment. After 5 minutes, remove it to obtain the prepared nanofiltration membrane.

[0096] Example 3

[0097] 1) Prepare a first aqueous phase solution containing polyetherimide (0.5% by mass), tobramycin (0.5% by mass), and sodium hydroxide (1.2% by mass). Prepare a 0.2% (w / w) solution of trimesoyl chloride in n-heptane as the oil phase solution. Prepare a second aqueous phase solution containing tobramycin (0.6% by mass) and sodium hydroxide (1.2% by mass).

[0098] 2) Pour the first aqueous phase solution onto the base film surface, let it stand for 30 seconds, then pour it off and use a rubber roller to remove excess first aqueous phase solution from the base film surface; pour the organic phase solution onto the base film surface, react for 1 minute, then pour off excess oil phase solution and use a rubber roller to remove excess oil phase solution from the base film surface.

[0099] 3) Pour the second aqueous solution onto the surface of the base film, react for 30 seconds, and then pour off the excess second aqueous solution;

[0100] 4) Pour the organic phase solution onto the surface of the base film, react for 30 seconds, and then pour off the excess oil phase solution;

[0101] 5) Place the membrane in an oven at 80°C for heat treatment. After 5 minutes, remove the membrane to obtain the prepared nanofiltration membrane.

[0102] Example 4

[0103] 1) Prepare a first aqueous phase solution containing polyetherimide (0.6% by mass), tobramycin (0.4% by mass), and sodium hydroxide (1% by mass). Prepare a 0.25% (w / w) heptane solution of trimesoyl chloride as the oil phase solution. Prepare a second aqueous phase solution containing tobramycin (0.6% by mass) and sodium hydroxide (1% by mass).

[0104] 2) Pour the first aqueous phase solution onto the base film surface, let it stand for 1 minute, then pour it off. Use a rubber roller to remove any excess first aqueous phase solution from the base film surface.

[0105] 3) Pour the organic phase solution onto the base film surface, react for 2 minutes, then pour off the excess oil phase solution and use a rubber roller to remove the excess oil phase solution from the base film surface;

[0106] 4) Pour the second aqueous solution onto the surface of the base film, react for 30 seconds, and then pour off the excess second aqueous solution;

[0107] 5) Place the base membrane in an oven at 80°C for heat treatment. After 5 minutes, remove it to obtain the prepared nanofiltration membrane.

[0108] Example 5

[0109] 1) Prepare an aqueous solution containing polyetherimide (0.6% by mass), tobramycin (0.4% by mass), and sodium hydroxide (1% by mass). Prepare a 0.2% (w / w) heptane solution of pyromellitic trimethylol chloride as the oil phase solution.

[0110] 2) Pour the aqueous solution onto the base film surface, let it stand for 30 seconds, then pour it off, and use a rubber roller to remove excess aqueous solution from the base film surface;

[0111] 3) Pour the organic phase solution onto the surface of the base film, react for 30 seconds, and then pour off the excess oil phase solution;

[0112] 4) Place the base membrane in an oven at 80°C for heat treatment. After 5 minutes, remove it to obtain the prepared nanofiltration membrane.

[0113] Comparative Example 1

[0114] 1) Prepare an aqueous solution containing polyetherimide (0.5% by mass) and sodium hydroxide (1% by mass), and prepare a 0.2% by mass solution of pyromellitic chloride in n-heptane as an oil phase solution.

[0115] 2) Pour the aqueous solution onto the base film surface, let it stand for 30 seconds, then pour it off, and use a rubber roller to remove excess aqueous solution from the base film surface;

[0116] 3) Pour the oil phase solution onto the surface of the base film, react for 30 seconds, and then pour off the excess oil phase solution;

[0117] 4) Place the base membrane in an oven at 80°C for heat treatment. After 5 minutes, remove it to obtain the prepared nanofiltration membrane.

[0118] Comparative Example 2

[0119] 1) Prepare an aqueous solution containing tobramycin (0.6% by mass) and sodium hydroxide (1% by mass), and prepare a 0.2% by mass solution of pyromellitic chloride in n-heptane as the oil phase solution.

[0120] 2) Pour the aqueous solution onto the base film surface, let it stand for 30 seconds, then pour it off, and use a rubber roller to remove excess aqueous solution from the base film surface;

[0121] 3) Pour the organic phase solution onto the surface of the base film, react for 30 seconds, and then pour off the excess oil phase solution;

[0122] 4) Place the base membrane in an oven at 80°C for heat treatment. After 5 minutes, remove it to obtain the prepared nanofiltration membrane.

[0123] The nanofiltration membrane provided in this invention includes a base membrane and a separation layer disposed on the base membrane, the separation layer comprising a polymer based on tobramycin. Thus, tobramycin provides the nanofiltration membrane with a large number of amino and hydroxyl groups. The amino groups generate electrostatic interactions, selectively separating lithium ions from other ions and effectively retaining other ions, thereby improving the selectivity of the nanofiltration membrane. Simultaneously, the amino and hydroxyl groups provided by tobramycin control the formation of a relatively loose separation layer in the nanofiltration membrane, improving its permeability and effectively increasing its treatment efficiency. The following specific experimental data illustrates some of the advantages of this invention compared to the prior art.

[0124] Figure 1 This is a SEM characterization image of the nanofiltration membrane surface provided in the embodiments of the present invention. The nanofiltration membranes of Example 1 and Comparative Example 1 were observed using a scanning electron microscope (SEM).

[0125] visible, Figure 1 Image (a) shows the SEM characterization of the nanofiltration membrane from Example 1. Figure 1 Figure (b) shows the SEM characterization of the nanofiltration membrane in Comparative Example 1. It can be seen that the nanofiltration membrane prepared with tobramycin in Example 1 has a more porous surface structure and more pores, which increases the water permeation flux and thus improves the water flux of the nanofiltration membrane. In contrast, the nanofiltration membrane prepared without tobramycin in Comparative Example 1 has a dense surface with no obvious pores, resulting in a lower water flux compared to Example 1 and thus lower efficiency in treating lithium-containing solutions.

[0126] Figure 2 This is a schematic diagram of the water contact angle test on the surface of the nanofiltration membrane provided in the embodiment of the present invention. Water droplets were added to the nanofiltration membranes of Example 1 and Comparative Example 1, and the water contact angles on the surfaces of the nanofiltration membranes of Example 1 and Comparative Example 1 were observed using a scanning electron microscope (SEM).

[0127] visible, Figure 2 Image (a) shows the SEM characterization of the nanofiltration membrane from Example 1. Figure 2 Figure (b) shows the SEM characterization of the nanofiltration membrane in Comparative Example 1. It can be seen that the nanofiltration membrane prepared with tobramycin in Example 1 has a smaller water contact angle, indicating better hydrophilicity and thus improved water flux. In contrast, the nanofiltration membrane prepared without tobramycin in Comparative Example 1 has a larger water contact angle and therefore cannot achieve the same water flux as in Example 1, resulting in lower efficiency in treating lithium-containing solutions.

[0128] After drying the nanofiltration membrane in an oven at 40°C for 24 hours, the surface charge of the nanofiltration membrane was analyzed using a Zeta potentiometer. The experimental results are shown in Table 1.

[0129] Table 1. Nanofiltration membrane surface charge test

[0130]

[0131] It is evident that the charge amounts of Examples 1-4 are significantly higher than those of Comparative Examples 1-2, and the charge amount of Example 5 is higher than that of Comparative Example 2. This demonstrates that adding tobramycin to the nanofiltration membrane can effectively improve its positive charge, enabling the nanofiltration membrane to effectively and selectively separate lithium ions.

[0132] The performance of the nanofiltration membrane was tested using a cross-flow testing device. The prepared membrane was cut to a suitable size and placed in a membrane tank. The test was conducted under the conditions of 1.3 MPa pressure and 25℃ temperature. The feed solution used was an aqueous solution of 500 ppm lithium ions + 1500 ppm magnesium ions, with a magnesium-to-lithium ratio of 3 and a pH of 3.5-4.5. Before testing, the nanofiltration membrane needed to be pre-pressed for 30 minutes to allow the membrane performance to stabilize. The experimental results are shown in Table 2.

[0133] Table 2 Nanofiltration Membrane Selection Performance Test

[0134] Serial Number Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Water flux / LMH 204 208 209 218 158 132 350 Lithium Retention Rate / % -42.3 -35.6 -34.6 -32.1 -35.3 -15.3 -45.3 Magnesium Retention Rate / % 98.4 97.5 97.4 97.4 97.6 95.2 54.5

[0135] As can be seen, the nanofiltration membranes prepared in Examples 1-5 exhibit magnesium ion rejection rates higher than 97% and lithium ion rejection rates lower than -30%, achieving selective separation of lithium ions. Their magnesium and lithium ion rejection rates are superior to those of Comparative Examples 1-2. The water flux of Examples 1-4 is higher than that of Comparative Example 1. Example 5, due to the absence of multiple interfacial polymerization to obtain the composite separation layer, has a lower water flux compared to Examples 1-4.

[0136] Comparative Example 1, without the addition of tobramycin, showed excessively high density and low positive charge, resulting in lower water flux, magnesium ion rejection rate, and lithium ion rejection rate compared to Examples 1-4.

[0137] Comparative Example 2: The nanofiltration membranes prepared with tobramycin were not well formed and had an overly porous surface. Although they had good water flux, their magnesium ion rejection rate was too low.

[0138] The present invention provides a detailed description of a nanofiltration membrane and its preparation method. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A nanofiltration membrane, characterized in that, The nanofiltration membrane includes a base membrane and a separation layer disposed on the base membrane; the separation layer specifically includes a polymer based on tobramycin, polyamines, and acyl chloride compounds.

2. The nanofiltration membrane according to claim 1, characterized in that, The nanofiltration membrane has a positively charged surface.

3. The nanofiltration membrane according to claim 1, characterized in that, The nanofiltration membrane is used to separate polyvalent positive ions and lithium ions in a lithium-containing solution.

4. The nanofiltration membrane according to claim 3, characterized in that, The nanofiltration membrane has a lithium ion rejection rate of less than -30% and a polyvalent positive ion rejection rate of more than 97%.

5. The nanofiltration membrane according to claim 1, characterized in that, The water flux of the nanofiltration membrane is greater than 200 LMH.

6. A method for preparing a nanofiltration membrane, characterized in that, The method includes: A first aqueous phase solution and an oil phase solution are disposed on the surface of the base film; wherein, the first aqueous phase solution includes tobramycin; The first aqueous solution and the oil solution polymerize to form a separation layer disposed on the base film; the separation layer specifically comprises a polymer based on tobramycin, polyamines, and acyl chloride compounds.

7. The method according to claim 6, characterized in that, The step of setting the first aqueous phase solution and the oil phase solution on the surface of the base film includes: A first aqueous solution is disposed on the surface of the base film; After the first aqueous phase solution is uniformly distributed on the surface of the base film, the oil phase solution is then placed on the base film.

8. The method according to claim 6, characterized in that, The first aqueous solution further includes polyamines, and the oil phase solution includes acyl chloride compounds; The step of polymerizing the first aqueous solution with the oil solution to form a separation layer on the base film includes: The polyamine and tobramycin in the first aqueous solution polymerize with the acyl chloride compound in the oil solution to form a separation layer disposed on the base film. The separation layer comprises a polymer based on tobramycin, polyamine, and acyl chloride compound.

9. The method according to claim 6 or 8, characterized in that, The method includes: A second aqueous solution is disposed on the surface of the separation layer to form a composite separation layer; wherein the second aqueous solution includes tobramycin.

10. The method according to claim 9, characterized in that, The mass fraction of tobramycin in the first aqueous solution is 0.02%-1%, and / or the mass fraction of tobramycin in the second aqueous solution is 0.02%-1%.

11. The method according to claim 8, characterized in that, The mass fraction of the polyamine in the first aqueous phase solution is 0.02%-1%, and / or the mass fraction of the acyl chloride compound in the oil phase solution is 0.02%-3%.

12. The method according to claim 9, characterized in that, The first aqueous solution further includes an acid-absorbing agent, and / or the second aqueous solution further includes an acid-absorbing agent; The acid absorbent includes one or more of the following: sodium hydroxide, triethylamine, potassium phosphate, sodium carbonate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate, and potassium dihydrogen phosphate.

13. The method according to claim 8, characterized in that, The oil phase solution also includes an oily solvent, which includes one or more of n-heptane, n-hexane, and isoparaffin solvents.

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