Nanofiltration membrane and preparation method thereof

Abstract

The embodiment of the invention provides a nanofiltration membrane and a preparation method thereof. The nanofiltration membrane provided by the embodiment of the invention comprises a base membrane and a separation layer arranged on the base membrane, and the separation layer comprises a polymer formed based on tobramycin. Therefore, a large number of amino groups and hydroxyl groups can be provided for the nanofiltration membrane through the tobramycin, lithium ions and other ions are selectively separated through electrostatic interaction generated by the amino groups, the other ions can be effectively intercepted, and the selectivity of the nanofiltration membrane is improved. Meanwhile, an amino group and a hydroxyl group provided by the tobramycin are used for controlling the nanofiltration membrane to form a relatively loose separation layer, so that the permeability of the nanofiltration membrane can be improved, and the treatment efficiency of the nanofiltration membrane is effectively improved.

Description

Technical Field

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

[0002] Lithium is an important energy metal and is currently widely used in energy storage technologies such as batteries. my country's lithium resources usually exist in the form of solutions, which usually contain lithium ions and other ions. In order to extract lithium, lithium ions and other ions need to be separated.

[0003] In the prior art, lithium ions can be separated from other ions by selective ion separation methods, such as ultrafiltration, nanofiltration, and reverse osmosis. However, the existing selective ion separation methods usually have poor selectivity and may not be able to well intercept other ions. In addition, there may be poor permeability, resulting in low treatment efficiency. Summary of the invention

[0004] The embodiment of 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 to lithium ions and maintain good permeability.

[0005] An embodiment of the present invention discloses a nanofiltration membrane, which includes a base membrane and a separation layer arranged on the base membrane, wherein the separation layer includes a polymer formed based on tobramycin.

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

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

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

[0009] Optionally, the nanofiltration membrane has a retention rate of less than -30% for lithium ions and a retention rate of greater than 97% for multivalent positive ions.

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

[0011] The present 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 phase solution and the oil phase solution are polymerized to form a separation layer disposed on the base film; the separation layer includes a polymer formed based on tobramycin.

[0014] Optionally, the step of providing a first aqueous solution and an oily solution on the surface of the base film comprises:

[0015] Disposing a first aqueous solution on the surface of the base film;

[0016] After the first aqueous phase solution is evenly distributed on the surface of the base film, the oil phase solution is disposed on the base film.

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

[0018] The step of polymerizing the first aqueous phase solution and the oil phase solution to form a separation layer disposed on the base film comprises:

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

[0020] Optionally, the method comprises:

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

[0022] Optionally, the mass fraction of tobramycin in the first aqueous phase solution is 0.02%-1%, and / or the mass fraction of tobramycin in the second aqueous phase 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 phase solution further includes an acid absorber, and / or the second aqueous phase solution further includes an acid absorber;

[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, and the oily solvent includes one or more of n-heptane, n-hexane, and isoparaffin solvents.

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

[0028] The nanofiltration membrane provided by the embodiment of the present invention includes a basement membrane and a separation layer arranged on the basement membrane, wherein the separation layer includes a polymer formed based on tobramycin. Thus, a large number of amino groups and hydroxyl groups can be provided to the nanofiltration membrane by tobramycin, and the electrostatic effect generated by the amino groups can selectively separate lithium ions from other ions, and other ions can be effectively trapped, thereby improving the selectivity of the nanofiltration membrane. At the same time, the amino groups and hydroxyl groups provided by tobramycin control the nanofiltration membrane to form a relatively loose separation layer, thereby improving the permeability of the nanofiltration membrane and effectively improving the processing efficiency of the nanofiltration membrane. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0030] Figure 2 It is a schematic diagram of testing the water contact angle on the surface of the nanofiltration membrane provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0032] An embodiment of the present invention discloses a nanofiltration membrane, which includes a base membrane and a separation layer arranged on the base membrane, wherein the separation layer includes a polymer formed based on tobramycin.

[0033] In an embodiment of the present invention, the nanofiltration membrane may include a base membrane and a separation layer. The base membrane may generally be used to provide mechanical support for the separation layer. The base membrane may generally be made of a material having a porous structure and stable chemical properties. The porous structure may allow water and other solutes to pass through while supporting the separation layer. The chemical stability may provide a longer service life for the nanofiltration membrane.

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

[0035] In an embodiment of the present invention, the separation layer can be used to achieve selective separation of lithium ions based on pore size and electrostatic action. Wherein, the pore size of the separation layer can be at the nanometer level, thus, the nanofiltration membrane can isolate solutes with excessive molecular weight through the pore size. At the same time, the separation layer includes a polymer formed based on tobramycin, and a large number of amino groups can be provided to the separation layer through tobramycin. Wherein the amino group can be hydrolyzed in water, so that the nanofiltration membrane is charged around, thereby generating electrostatic action, and the electrostatic action can produce different repulsive effects on ions of different electric valences. For ions with high electric valence, it can be subjected to a greater repulsive force, thereby being intercepted by the separation layer, and for ions with low electric valence, such as lithium ions, it can be subjected to a smaller repulsive force, so that it can pass through the separation layer normally. Thus, it is possible to separate lithium ions from other ions, thereby selectively screening and obtaining lithium ions.

[0036] At the same time, in the preparation process of nanofiltration membrane, tobramycin can provide a large number of amino groups and hydroxyl groups, which can have good hydrophilicity. In the process of preparing nanofiltration membrane based on interfacial polymerization, it is necessary to react the compounds in the aqueous solution and the oil phase solution at the interface of the two phases to form a polymer, thereby forming a separation layer. At this time, the amino group and hydroxyl group of tobramycin can attract the compounds in the aqueous solution through the intermolecular force, reduce the migration rate of the compounds in the aqueous solution to the interface of the two phases, so that the reaction process of preparing nanofiltration membrane by interfacial polymerization can be relatively mild, forming a relatively loose separation layer, so that the solution can pass through the nanofiltration membrane more easily, keep the nanofiltration membrane has good permeability, and improve the processing efficiency of separating lithium ions in the solution.

[0037] In one embodiment of the present invention, the separation layer specifically includes a polymer based on tobramycin, polyamine, and acyl chloride compound.

[0038] Specifically, the separation layer may include a polymer formed based on tobramycin, a polyamine, and an acyl chloride compound. The polyamine may react with the acyl chloride compound to form a polymer containing an amino group, so that the separation layer may generate an electrostatic effect to achieve separation of ions of different valences. By further adding tobramycin to participate in the reaction between the polyamine and the acyl chloride compound, more amino groups and hydroxyl groups may be introduced into the polymer, thereby further improving the interception effect of the separation layer on high-valence ions and improving the effect of selective separation of low-valence lithium ions.

[0039] As a specific example of the present invention, the polyamine may include polyetherimide, piperazine, polyethyleneimine, metaphenylenediamine, paraphenylenediamine, etc. The acid chloride compound may include terephthaloyl chloride, isophthaloyl chloride, trimesoyl chloride, etc.

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

[0041] Generally speaking, nanofiltration membranes can usually have a negatively charged surface. Nanofiltration membranes with negatively charged surfaces can achieve selective separation of lithium ions by attracting positively charged lithium ions through negative charges and repelling negatively charged ions. However, solutions containing lithium ions in nature may also contain positively charged ions of other charges, which are usually attracted by negatively charged nanofiltration membranes, resulting in a low retention rate for other positively charged ions.

[0042] The main goal of separating lithium ions from lithium-containing solutions is to separate lithium ions from other positively charged ions to prevent positively charged ions from interfering with the subsequent extraction process of lithium ions. Therefore, in the embodiment of the present invention, by adding tobramycin, during the polymerization process of the polyamine and the acyl chloride compound, the acyl chloride groups in the acyl chloride compound can be fully reacted with the polyamine and tobramycin, so that the surface of the nanofiltration membrane mainly contains amino groups, and the surface of the nanofiltration membrane is positively charged.

[0043] Positively charged nanofiltration membranes can have a certain degree of repulsion on positively charged ions, but positively charged ions of different charges are subject to different repulsion forces. For lithium ions, due to their low charge, they can be subject to less repulsion, so they can pass through the nanofiltration membrane normally. Other positively charged ions can be subject to greater repulsion than lithium ions, so that other positively charged ions are retained by the nanofiltration membrane, thereby effectively achieving selective separation of lithium ions.

[0044] In one embodiment of the present invention, the nanofiltration membrane is used to separate multivalent 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 a lithium-containing solution. The lithium-containing solution may generally contain lithium ions and multivalent positive ions. The nanofiltration membrane generates different repulsive forces on positive ions of different valences, so that the lithium ions in the lithium-containing solution can pass through the nanofiltration membrane normally and the 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 may be salt lake brine. Salt lake brine may be the main supply route for lithium resources. Salt lake brine mainly contains a large amount of magnesium ions and lithium ions, and the magnesium ion content may be much higher than that of lithium ions. The magnesium / lithium mass ratio in most salt lake brines is higher than 40. Since magnesium ions and lithium ions have similar hydration radii, magnesium ions and lithium ions behave similarly in aqueous solutions, making it difficult to separate them simply by physical methods. At the same time, the chemical properties of magnesium ions and lithium ions are similar, making it difficult to separate magnesium ions and lithium ions simply by chemical reactions.

[0047] In an embodiment of the present invention, a nanofiltration membrane is provided to produce different repulsive forces on positively charged ions of different electric valences, so that lithium ions in the salt lake brine can pass through the nanofiltration membrane normally, while magnesium ions are retained. Thus, the magnesium ions existing in large quantities in the salt lake brine can be effectively separated from the lithium ions, thereby preventing the magnesium ions from affecting the subsequent further extraction of lithium ions.

[0048] In one embodiment of the present invention, the nanofiltration membrane has a retention rate of less than -30% for lithium ions and a retention rate of more than 97% for multivalent positive ions.

[0049] In the embodiment of the present invention, the nanofiltration membrane can generate a repulsive force through electrostatic action, allowing lithium ions to pass through the nanofiltration membrane while intercepting multivalent positive ions to pass through the nanofiltration membrane. By arranging a polymer formed based on tobramycin in the separation layer of the nanofiltration membrane, it can mainly contain amino groups, and the hydrolysis reaction of the amino groups in water makes the surface of the nanofiltration membrane positively charged. The positively charged nanofiltration membrane can effectively intercept multivalent positive ions, and the interception rate of multivalent positive ions is greater than 97%. At the same time, the positive charge amount on the surface of the nanofiltration membrane in the embodiment of the present invention is moderate, and lithium ions with low electric valence can pass through the nanofiltration membrane normally, and its interception rate of lithium ions is less than -30%. It can be seen that the nanofiltration membrane of the embodiment of the present invention can have a higher selectivity for lithium ions, and can better achieve the separation between lithium ions and multivalent positive ions.

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

[0051] Specifically, in the preparation process of nanofiltration membrane, tobramycin can provide a large amount of amino groups and hydroxyl groups, which can have good hydrophilicity. In the process of preparing nanofiltration membrane based on interfacial polymerization, it is necessary to react to form polymers at the interface of two phases by the compounds in aqueous solution and oil phase solution, so as to form a separation layer. At this time, the amino group and hydroxyl group of tobramycin can attract the compounds in the aqueous solution by the intermolecular force, reduce the migration rate of the compounds in the aqueous solution to the interface of two phases, so that the reaction process of preparing nanofiltration membrane by interfacial polymerization can be relatively gentle, form a relatively loose separation layer, so that the solution can be more easily passed through the nanofiltration membrane, keep the nanofiltration membrane has good permeability, the water flux of the nanofiltration membrane is greater than 200LMH, so that the nanofiltration membrane can process more solutions per unit time, and the processing efficiency of separating lithium ions can be improved.

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

[0053] Step 101, placing a first aqueous solution and an oily solution on the surface of the basement membrane; wherein the first aqueous solution comprises tobramycin;

[0054] Step 102: The first aqueous solution and the oily solution are polymerized to form a separation layer disposed on the base film; the separation layer includes a polymer formed based on tobramycin.

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

[0056] In an embodiment of the present invention, the first aqueous phase solution includes tobramycin. In the process of polymerization reaction of compounds in the first aqueous phase solution and the oil phase solution, tobramycin can be further introduced so that the polymer in the separation layer mainly contains amino groups. The amino group can be hydrolyzed in water, so that the nanofiltration membrane is charged around, thereby generating electrostatic effects, which can produce different repulsive effects on ions of different valences. For ions with high valences, they can be subjected to greater repulsive forces, thereby being intercepted by the separation layer, and for ions with low valences, such as lithium ions, they can be subjected to smaller repulsive forces, thereby being able to pass through the separation layer normally. Thus, it is possible to separate lithium ions from other ions, thereby selectively screening and obtaining lithium ions.

[0057] At the same time, in the preparation process of the nanofiltration membrane, tobramycin can provide a large number of amino groups and hydroxyl groups, which can have good hydrophilicity. The compounds in the first aqueous phase solution and the oil phase solution can produce a polymerization reaction at the interface of the aqueous phase and the oil phase. In the process of forming the polymer, the amino group and hydroxyl group of tobramycin can attract the compounds in the aqueous phase solution through the intermolecular force, reducing the migration rate of the compounds in the aqueous phase solution to the interface of the two phases, so that the reaction process of preparing the nanofiltration membrane by the interfacial polymerization method can be relatively mild, forming a relatively loose separation layer, so that the solution can pass through the nanofiltration membrane more easily, maintaining the good permeability of the nanofiltration membrane, and improving the processing efficiency of separating lithium ions in the solution.

[0058] In one embodiment of the present invention, the step of providing the first aqueous solution and the oil phase solution on the surface of the base film comprises:

[0059] S11, disposing a first aqueous solution on the surface of the base film;

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

[0061] In a specific implementation, the first aqueous phase solution can be firstly arranged on the surface of the base film and allowed to stand for a period of time. The first aqueous phase solution can be spread on the surface of the base film. After the first aqueous phase solution is evenly distributed on the surface of the base film, the oil phase solution is arranged on the base film, so that the aqueous phase solution and the oil phase solution form a two-phase interface that can cover the base film as much as possible, thereby forming a better separation layer on the surface of the base film.

[0062] In order to make the separation layer evenly distributed on the surface of the base film with moderate thickness, rollers can be used to assist in stretching and remove excess first aqueous phase solution and oil phase solution during the process of setting the first aqueous phase solution and the oil phase solution, so that the first aqueous phase solution and the oil phase solution are evenly distributed on the surface of the base film.

[0063] As a specific example of the present invention, the first aqueous phase solution can be first added to the surface of the base film, and after standing for 30s-10min, the excess first aqueous phase solution can be poured out, and the excess first aqueous phase solution on the surface of the base film can be further removed by a rubber roller, so that the first aqueous phase solution is evenly distributed on the surface of the base film without excess water overflowing. Thereafter, the oil phase solution is disposed on the base film, and the compound and tobramycin in the aqueous phase solution can react with the compound in the oil phase solution. After the reaction for 30s-10min, the excess oil phase solution is poured out, and the excess oil phase solution on the surface of the base film is removed by a rubber roller.

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

[0065] The step of polymerizing the first aqueous phase solution and the oil phase solution to form a separation layer disposed on the base film comprises:

[0066] S21, the polyamine and tobramycin in the first aqueous solution are polymerized with the acyl chloride compound in the oil phase solution to form a separation layer disposed on the base film, wherein the separation layer includes a polymer formed based on tobramycin, the polyamine, and the 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 an amino group, so that the separation layer can generate an electrostatic effect to achieve the separation of ions with different electric charges. 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 groups and hydroxyl groups can be introduced into the polymer, thereby further improving the interception effect of the separation layer on high-charge ions and improving the effect of selective separation of low-charge lithium ions.

[0068] As a specific example of the present invention, the polyamine may include polyetherimide, piperazine, polyethyleneimine, metaphenylenediamine, paraphenylenediamine, etc. The acid chloride compound may include terephthaloyl chloride, isophthaloyl chloride, trimesoyl chloride, etc.

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

[0070] S31, disposing a second aqueous phase solution on the surface of the separation layer to form a composite separation layer; wherein the second aqueous phase solution comprises tobramycin.

[0071] In an embodiment of the present invention, in order to ensure that the surface of the nanofiltration membrane is positively charged, a composite separation layer can be formed by multiple interfacial polymerization methods, so that the acyl chloride groups on the surface of the nanofiltration membrane react completely. Thus, a second aqueous phase solution can be arranged on the surface of the separation layer. The second aqueous phase solution includes tobramycin, and the acyl chloride groups in the oil phase solution are completely reacted through the amino groups and hydroxyl groups provided by tobramycin, and the surface of the composite separation layer can contain a large number of amino groups and hydroxyl groups provided by tobramycin, further improving the water flux of the nanofiltration membrane as a whole.

[0072] Optionally, the first aqueous phase solution and the oil phase solution are polymerized to form a separation layer disposed on the base membrane, and a second aqueous phase solution is further disposed on the surface of the separation layer to form a composite separation layer. At this time, the composite separation layer is initially formed, but the composite separation layer is not solidified on the surface of the base membrane, and the solvents in the first aqueous phase solution, the oil phase solution, and the second aqueous phase solution are not removed from the surface of the base membrane. At this time, the base membrane can be placed in an oven at 50°C-120°C for heat treatment to solidify the composite separation layer and remove excess solvent, and then taken out after 3-30 minutes to obtain a prepared nanofiltration membrane.

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

[0074] In the embodiment of the present invention, tobramycin needs a suitable addition amount. If the addition amount is too little, it may cause the presence of unreacted acyl chloride groups in the separation layer, so that the nanofiltration membrane is negatively charged, and the effect of selective separation of lithium ions by electrostatic action cannot be achieved. If the addition amount is too much, the electrostatic action on the surface of the nanofiltration membrane may be too strong, not only having a trapping effect on multivalent positive ions, but also trapping lithium ions together, and the effect of selective separation of lithium ions cannot be achieved. Thus, 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 this mass fraction, tobramycin can provide a suitable amount of amino groups and hydroxyl groups, which can achieve the effect of 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 phase solution and the mass fraction of the acyl chloride compound in the oil phase solution can affect the thickness of the prepared separation layer. In order to enable the nanofiltration membrane to selectively separate lithium ions without affecting the water flux of the nanofiltration membrane due to the excessive thickness of the separation layer, the mass fraction of the polyamine in the first aqueous phase solution can be set to 0.02%-1%, and the mass fraction of the acyl chloride compound in the oil phase solution can be set to 0.02%-3%. The separation layer formed at this time can have a moderate thickness.

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

[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 of the polyamine and tobramycin in the first aqueous phase solution with the acyl chloride compound in the oil phase solution, acidic byproducts may be generated, which may affect the reaction and cause the separation layer to fail to form well. To this end, an acid absorber may be added to the first aqueous phase solution and / or the second aqueous phase solution to neutralize the acidic byproducts during the reaction to ensure that the separation layer is formed normally.

[0080] In a specific implementation, the acid absorber can be one or more of 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 also includes an oily solvent, and the oily solvent includes one or more of n-heptane, n-hexane, and isoparaffin solvents.

[0082] Specifically, the oil phase solution also includes an oily solvent. In order to promote the interfacial polymerization reaction, a solvent with good solubility of the acyl chloride compound and incompatible with water, such as one or more of n-heptane, n-hexane, and isoparaffin solvents (such as ISOPARG) can be selected as the oily solvent.

[0083] In order to enable those skilled in the art to better understand the present invention, the preparation method of the nanofiltration membrane of the present invention is described below through a number of specific examples.

[0084] Example 1

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

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

[0087] 3) Pour the organic phase solution onto the surface of the basement membrane, react for 1 minute, pour out the excess oil phase solution, and use a rubber roller to remove the excess oil phase solution on the surface of the basement membrane;

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

[0089] 5) The base film was placed in an oven at 80° C. for heat treatment and taken out after 5 minutes to obtain a prepared nanofiltration membrane.

[0090] Example 2

[0091] 1) Prepare a first aqueous phase solution containing polyetherimide (mass fraction of 0.5%), tobramycin (mass fraction of 0.6%) and triethylamine (mass fraction of 1%), prepare a 0.2% n-heptane solution of trimesoyl chloride as an oil phase solution. Prepare a second aqueous phase solution containing tobramycin (mass fraction of 0.6%) and triethylamine (mass fraction of 1%).

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

[0093] 3) Pour the organic phase solution onto the surface of the basement membrane, react for 1 minute, pour out the excess oil phase solution, and use a rubber roller to remove the excess oil phase solution on the surface of the basement membrane;

[0094] 4) Pour the second aqueous phase solution onto the surface of the basement membrane, react for 30 seconds, and then pour out the excess second aqueous phase solution;

[0095] 5) The base film was placed in an oven at 80° C. for heat treatment and taken out after 5 minutes to obtain a prepared nanofiltration membrane.

[0096] Example 3

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

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

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

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

[0101] 5) The membrane was placed in an oven at 80° C. for heat treatment and taken out after 5 minutes to obtain a prepared nanofiltration membrane.

[0102] Example 4

[0103] 1) Prepare a first aqueous phase solution containing polyetherimide (mass fraction 0.6%), tobramycin (mass fraction 0.4%) and sodium hydroxide (mass fraction 1%). Prepare a 0.25% trimesoyl chloride n-heptane solution as an oil phase solution. Prepare a second aqueous phase solution containing tobramycin (mass fraction 0.6%) and sodium hydroxide (mass fraction 1%).

[0104] 2) Pour the first aqueous phase solution onto the surface of the base film, let it stand for 1 minute, then pour it out and use a rubber roller to remove the excess first aqueous phase solution on the surface of the base film.

[0105] 3) Pour the organic phase solution onto the surface of the basement membrane, react for 2 minutes, pour out the excess oil phase solution, and use a rubber roller to remove the excess oil phase solution on the surface of the basement membrane;

[0106] 4) Pour the second aqueous phase solution onto the surface of the basement membrane, react for 30 seconds, and then pour out the excess second aqueous phase solution;

[0107] 5) The base film was placed in an oven at 80° C. for heat treatment and taken out after 5 minutes to obtain a prepared nanofiltration membrane.

[0108] Example 5

[0109] 1) Prepare an aqueous phase solution containing polyetherimide (mass fraction 0.6%), tobramycin (mass fraction 0.4%) and sodium hydroxide (mass fraction 1%). Prepare a 0.2% mass fraction of trimesoyl chloride n-heptane solution as an oil phase solution.

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

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

[0112] 4) The base film was placed in an oven at 80° C. for heat treatment and taken out after 5 minutes to obtain a prepared nanofiltration membrane.

[0113] Comparative Example 1

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

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

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

[0117] 4) The base film was placed in an oven at 80° C. for heat treatment and taken out after 5 minutes to obtain a prepared nanofiltration membrane.

[0118] Comparative Example 2

[0119] 1) An aqueous phase solution containing tobramycin (mass fraction of 0.6%) and sodium hydroxide (mass fraction of 1%) was prepared, and a n-heptane solution of trimesoyl chloride with a mass fraction of 0.2% was prepared as an oil phase solution.

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

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

[0122] 4) The base film was placed in an oven at 80° C. for heat treatment and taken out after 5 minutes to obtain a prepared nanofiltration membrane.

[0123] The nanofiltration membrane provided by the embodiment of the present invention comprises a basement membrane and a separation layer arranged on the basement membrane, wherein the separation layer comprises a polymer formed based on tobramycin. Thus, a large number of amino groups and hydroxyl groups can be provided to the nanofiltration membrane by tobramycin, and the electrostatic effect is generated by the amino groups to selectively separate lithium ions from other ions, and other ions can be effectively trapped, thereby improving the selectivity of the nanofiltration membrane. At the same time, the amino groups and hydroxyl groups provided by tobramycin are used to control the nanofiltration membrane to form a relatively loose separation layer, which can improve the permeability of the nanofiltration membrane and effectively improve the processing efficiency of the nanofiltration membrane. The following is an explanation of some advantages of the embodiments of the present invention compared to the prior art by specific experimental data.

[0124] Figure 1 The nanofiltration membranes of Example 1 and Comparative Example 1 were observed using a scanning electron microscope (SEM).

[0125] visible, Figure 1 (a) is the SEM characterization of the nanofiltration membrane of Example 1, Figure 1 (b) is the SEM characterization of the nanofiltration membrane of Example 1. It can be seen that the membrane surface structure of the nanofiltration membrane prepared by adding tobramycin in Example 1 is looser, and the membrane surface has more pores, which can increase the water permeation flux, thereby improving the water flux of the nanofiltration membrane. However, the nanofiltration membrane prepared without adding tobramycin in Comparative Example 1 has a dense surface and no obvious pores. Compared with Example 1, it cannot have a better water flux, resulting in a lower treatment efficiency for the lithium-containing solution.

[0126] Figure 2 Schematic diagram of water contact angle test on the surface of nanofiltration membrane provided by an embodiment of the present invention. Water droplets were dripped on 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 (a) is the SEM characterization of the nanofiltration membrane of Example 1, Figure 2 (b) is the SEM characterization of the nanofiltration membrane of Example 1. It can be seen that the nanofiltration membrane prepared by adding tobramycin in Example 1 has a smaller water contact angle, that is, its hydrophilicity is better, thereby improving the water flux of the nanofiltration membrane. However, the nanofiltration membrane prepared without adding tobramycin in Comparative Example 1 has a larger water contact angle, and cannot have a better water flux than Example 1, resulting in a lower treatment efficiency for the lithium-containing solution.

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

[0129] Table 1 Nanofiltration membrane surface charge test

[0130]

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

[0132] The performance of the nanofiltration membrane was tested using a cross-flow test device. The prepared membrane was cut into a suitable size and placed in a membrane pool. The test was performed under a pressure of 1.3 MPa and a temperature of 25°C. The raw material solution used was a 500 ppm lithium ion + 1500 ppm magnesium ion aqueous solution with a magnesium-to-lithium ratio of 3 and a pH of 3.5-4.5. Before the test, the nanofiltration membrane needed to be pre-pressed for 30 minutes to stabilize the membrane performance. The experimental results are shown in Table 2.

[0133] Table 2 Nanofiltration membrane selectivity 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] It can be seen that the nanofiltration membranes prepared in Examples 1 to 5 have a magnesium ion rejection rate higher than 97% and a lithium ion rejection rate lower than -30%, and can achieve selective separation of lithium ions. The magnesium ion rejection rate and lithium ion rejection rate are better than those in Comparative Examples 1 to 2. The water flux of Examples 1 to 4 is all due to Comparative Example 1. Since Example 5 does not use multiple interfacial polymerization to obtain a composite separation layer, its water flux is lower than that of Examples 1 to 4.

[0136] The nanofiltration membrane of Comparative Example 1 without tobramycin addition had too high density and low positive charge, and the water flux, magnesium ion retention rate, and lithium ion retention rate were all lower than those of Examples 1-4.

[0137] In Comparative Example 2, the nanofiltration membrane prepared using only tobramycin was not formed and had a too loose surface. Although it had a good water flux, the retention rate of magnesium ions was too low.

[0138] The above is a detailed introduction to a nanofiltration membrane and a preparation method thereof provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on 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, wherein the separation layer includes a polymer formed based on tobramycin.

2. The nanofiltration membrane according to claim 1, characterized in that The separation layer specifically includes a polymer based on tobramycin, polyamine, and an acid chloride compound.

3. The nanofiltration membrane according to claim 1, characterized in that The surface of the nanofiltration membrane is positively charged.

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

5. The nanofiltration membrane according to claim 4, characterized in that The nanofiltration membrane has a retention rate of less than -30% for lithium ions and a retention rate of more than 97% for multivalent positive ions.

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

7. A method for preparing a nanofiltration membrane, characterized in that: The method comprises: 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 oily solution are polymerized to form a separation layer disposed on the base film; the separation layer includes a polymer formed based on tobramycin.

8. The method according to claim 7, characterized in that The step of providing a first aqueous solution and an oil phase solution on the surface of the base film comprises: Disposing a first aqueous solution on the surface of the base film; After the first aqueous phase solution is evenly distributed on the surface of the base film, the oil phase solution is disposed on the base film.

9. The method according to claim 7, characterized in that: The first aqueous phase solution further comprises a polyamine, and the oil phase solution comprises an acyl chloride compound; The step of polymerizing the first aqueous phase solution and the oil phase solution to form a separation layer disposed on the base film comprises: The polyamine and tobramycin in the first aqueous solution are polymerized with the acyl chloride compound in the oil solution to form a separation layer disposed on the base film. The separation layer includes a polymer formed based on tobramycin, polyamine, and acyl chloride compound.

10. The method according to claim 7 or 9, characterized in that: The method comprises: A second aqueous phase solution is disposed on the surface of the separation layer to form a composite separation layer; wherein the second aqueous phase solution includes tobramycin.

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

12. The method according to claim 9, 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%.

13. The method according to claim 10, characterized in that The first aqueous phase solution further includes an acid absorber, and / or the second aqueous phase solution further includes an acid absorber; 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.

14. The method according to claim 9, characterized in that The oil phase solution also includes an oily solvent, and the oily solvent includes one or more of n-heptane, n-hexane, and isoparaffin solvents.

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