Modified lithium ion sieves and membranes with separation functionality and methods of making and using the same

Abstract

The application relates to the field of separation and purification, discloses modified lithium ion sieves and membranes with a separation function as well as preparation methods and applications of the modified lithium ion sieves and the membranes. The modified lithium ion sieve comprises a lithium ion sieve and polyvinyl alcohol coated on the lithium ion sieve, wherein the mass content of the polyvinyl alcohol is 0.5-5 wt% relative to the mass of the modified lithium ion sieve. The modified lithium ion sieve has good acid and alkali resistance, and when applied to a magnesium-lithium separation membrane, the separation efficiency of the magnesium-lithium separation membrane can be improved. The membrane has good acid and alkali resistance and stable structure, the modified lithium ion loaded on the membrane is not easy to fall off, and the membrane is suitable for long-term use.

Description

Technical Field

[0001] This invention relates to the field of separation and purification, specifically to a modified lithium-ion sieve and a membrane with separation function, as well as their preparation methods and applications. Background Technology

[0002] In recent years, with the widespread application of new energy vehicles, the demand for lithium energy has gradually increased. Extracting pure lithium resources from salt lakes is currently a key approach to obtaining lithium resources. However, my country's salt lake brines suffer from a high magnesium-to-lithium ratio (approximately 10-300). Lithium and magnesium ions have very similar radii and chemical properties, making separation difficult. Currently, membrane separation and adsorption methods are widely used in salt lake lithium extraction, and they are often used in combination. In the adsorption method, the adsorbent adsorbs in the brine, and then hydrochloric acid or similar substances are used as the desorption solution to obtain a solution containing lithium ions and a small amount of magnesium and other divalent ions. This solution is then further separated by nanofiltration (mainly magnesium-to-lithium separation). However, due to the presence of a large amount of H₂ in the desorption solution... + Therefore, nanofiltration membranes not only need to have good magnesium-lithium separation performance, but also good acid and alkali resistance.

[0003] However, currently commercially available nanofiltration membranes have poor lithium-ion permeability, low magnesium-lithium separation efficiency, and poor acid and alkali resistance, making them unsuitable for long-term use. Therefore, there is an urgent need to develop magnesium-lithium separation membranes with excellent separation performance and acid and alkali resistance. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of low magnesium-lithium separation efficiency and poor acid and alkali resistance in existing membrane products. This invention provides a modified lithium-ion sieve and a membrane with separation function, as well as their preparation methods and applications. The membrane has a thin and dense separation layer. When this modified lithium-ion sieve and membrane are used, higher magnesium-lithium separation efficiency and higher water flux can be obtained. Furthermore, the membrane has good acid and alkali resistance and a stable structure. Using this membrane for magnesium-lithium separation results in higher efficiency and is more suitable for long-term use.

[0005] To achieve the above objectives, a first aspect of the present invention provides a modified lithium-ion sieve, the modified lithium-ion sieve comprising a lithium-ion sieve and polyvinyl alcohol coating the lithium-ion sieve, wherein the mass content of polyvinyl alcohol relative to the mass of the modified lithium-ion sieve is 0.5-5 wt%.

[0006] The second aspect of the present invention provides a method for preparing a modified lithium-ion sieve, the method comprising: mixing polyvinyl alcohol and a lithium-ion sieve in a solution state to obtain a modified lithium-ion sieve, wherein the mass ratio of lithium-ion sieve to polyvinyl alcohol is (0.3-5):1.

[0007] A third aspect of the present invention provides a modified lithium-ion sieve prepared as described in the second aspect.

[0008] A fourth aspect of the present invention provides a membrane with a separation function, the membrane comprising a porous support layer, a separation layer, and a modified lithium-ion sieve as described in the first or third aspect, further loaded on the porous support layer and / or the separation layer.

[0009] The fifth aspect of the present invention provides a method for preparing a membrane with separation function, the method comprising: introducing a modified lithium-ion sieve as described in the first or third aspect during the preparation of the membrane.

[0010] The sixth aspect of the present invention provides a membrane with separation function prepared by the method described in the fifth aspect.

[0011] The seventh aspect of the present invention provides the application of a membrane with separation function as described in the fourth or sixth aspect in the separation of magnesium and lithium.

[0012] The modified lithium-ion sieve provided by this invention exhibits good acid and alkali resistance, and when applied to membranes used for magnesium-lithium separation, it can improve the separation efficiency of the magnesium-lithium separation membrane. In particular, according to the preferred method for preparing the magnesium-lithium separation membrane provided by this invention, the modified lithium-ion sieve is introduced during the preparation of the porous support layer, thus further ensuring that the resulting membrane has high magnesium-lithium separation efficiency and water flux. Furthermore, the membrane provided by this invention also has good acid and alkali resistance, stable structure, and the modified lithium ions loaded on it are not easily detached, making it suitable for long-term use. Detailed Implementation

[0013] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0014] In a first aspect, the present invention provides a modified lithium-ion sieve, the modified lithium-ion sieve comprising a lithium-ion sieve and polyvinyl alcohol coating the lithium-ion sieve, wherein the mass content of polyvinyl alcohol relative to the mass of the modified lithium-ion sieve is 0.5-5 wt%.

[0015] It is understood that the polyvinyl alcohol coating the lithium-ion screen refers to the polyvinyl alcohol coating layer formed on the outside of the lithium-ion screen.

[0016] The inventors of this invention discovered in their research that the modified lithium-ion sieve described above has strong acid and alkali resistance. Applying the modified lithium-ion sieve to a membrane used for magnesium-lithium separation can significantly improve the magnesium-lithium separation efficiency, while also ensuring that the membrane has a high water flux and high treatment efficiency.

[0017] According to the present invention, preferably, the polyvinyl alcohol content is 0.9-2.5 wt% relative to the total mass of the modified lithium-ion sieve (for example, it can be 0.9 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, and any two of the above values ​​within a range).

[0018] According to the present invention, preferably, the average thickness of the polyvinyl alcohol coating the lithium ion sieve is 1-20 nm, more preferably 2-8 nm (for example, it can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, or any two of the above values ​​within a range).

[0019] Within the aforementioned range, further improve the magnesium-lithium separation efficiency when the modified lithium-ion sieve is applied to the magnesium-lithium separation membrane.

[0020] According to the present invention, preferably, the average particle size of the modified lithium-ion sieve is 10nm-10μm, more preferably 20-520nm (for example, it can be 20nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 380nm, 400nm, 420nm, 450nm, 500nm, 520nm, and any two of the above values, or values ​​within the range).

[0021] According to the present invention, preferably, the lithium ion screen is a lithium manganese oxide type lithium ion screen and / or a lithium titanium oxide type lithium ion screen. For example, the lithium ion screen can be Li 1.33 Mn 1.67 O4, Li4Ti5O 12 and Li4Mn5O 12 At least one of them.

[0022] According to the present invention, preferably, the weight-average molecular weight of the polyvinyl alcohol is 20,000-40,000 g / mol.

[0023] Secondly, the present invention provides a method for preparing a modified lithium-ion sieve, the method comprising: mixing polyvinyl alcohol and a lithium-ion sieve in a solution state to obtain a modified lithium-ion sieve, wherein the mass ratio of the lithium-ion sieve to polyvinyl alcohol is (0.3-5):1.

[0024] Using the above method, polyvinyl alcohol can be coated onto the surface of a lithium-ion sieve to obtain a modified lithium-ion sieve. The modified lithium-ion sieve obtained in this way has strong acid and alkali resistance. Applying the above modified lithium-ion sieve to a membrane used for magnesium-lithium separation can significantly improve the magnesium-lithium separation efficiency, while also ensuring that the membrane has a high water flux and high treatment efficiency.

[0025] According to the present invention, preferably, the mass ratio of polyvinyl alcohol to lithium ion screen is (0.4-2):1.

[0026] According to the present invention, preferably, the mass concentration of polyvinyl alcohol in the solution is 0.1-5 wt% (for example, it can be 0.1 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, and any two of the above values ​​within a range).

[0027] According to the present invention, preferably, the mixing time is 2-4 hours (e.g., 2 hours, 3 hours, or 4 hours), and the mixing temperature is 20-40°C (e.g., 20°C, 22°C, 25°C, 28°C, 30°C, 32°C, 35°C, 38°C, 40°C, and values ​​within any two of the above values). Polyvinyl alcohol and lithium ion sieves can be mixed in water, and stirring can be performed during the above-mentioned mixing time.

[0028] According to the present invention, preferably, the average particle size of the lithium-ion sieve is 10nm-10μm, more preferably 20-500nm (for example, it can be 20nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 380nm, 400nm, 420nm, 450nm, 500nm, and any two of the above values, or values ​​within the range).

[0029] According to the present invention, preferably, the lithium ion screen is a lithium manganese oxide type lithium ion screen and / or a lithium titanium oxide type lithium ion screen. The lithium ion screen can be Li... 1.33 Mn 1.67 O4, Li4Ti5O 12 and Li4Mn5O 12 At least one of them.

[0030] According to the present invention, preferably, the weight-average molecular weight of the polyvinyl alcohol is 20,000-40,000 g / mol.

[0031] According to the present invention, preferably, the method further includes: performing solid-liquid separation on the mixed materials and drying the resulting solid material. The mixed materials can be separated by centrifugation. After centrifugation, the materials can be washed (2-4 times with distilled water) and ball-milled to improve the dispersibility of the materials (this can be done at room temperature for 4-8 hours), and then dried. The drying time can be 8-12 hours, and the temperature can be 80-90°C.

[0032] Thirdly, the present invention provides a modified lithium-ion sieve prepared by the method described in the second aspect.

[0033] Fourthly, the present invention provides a membrane with a separation function, the membrane comprising a porous support layer, a separation layer, and a modified lithium-ion sieve as described in the first or third aspect, further loaded on the porous support layer and / or the separation layer.

[0034] According to a particularly preferred embodiment of the present invention, a modified lithium-ion sieve is loaded on a porous support layer.

[0035] According to the present invention, preferably, the loading of the modified lithium-ion sieve relative to 1g of membrane is 1-100mg, more preferably 3-15mg (for example, it can be 3mg, 4mg, 5mg, 6mg, 7mg, 8mg, 9mg, 10mg, 11mg, 12mg, 13mg, 14mg, 15mg, and any two of the above values ​​within the range and values ​​within the range).

[0036] According to the present invention, preferably, the membrane with separation function comprises a substrate layer, a porous support layer and a separation layer in sequence, wherein the modified lithium ion sieve is loaded on the porous support layer.

[0037] According to the present invention, preferably, the thickness of the substrate layer is 30-150 μm, more preferably 50-120 μm (for example, it can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, or any two of the above values ​​within a range or range); the average pore size is 10-25 μm; and the porosity is 15-25%.

[0038] According to the present invention, preferably, the thickness of the porous support layer is 10-100 μm, more preferably 30-60 μm (for example, it can be 30 μm, 40 μm, 50 μm, 60 μm, or any two of the above values ​​within a range).

[0039] According to the present invention, preferably, the thickness of the separation layer is 80-110 nm, more preferably 85-95 nm (for example, it can be 85 nm, 86 nm, 87 nm, 88 nm, 89 nm, 90 nm, 91 nm, 92 nm, 93 nm, 94 nm, 95 nm, and any two of the above values, or values ​​within the range).

[0040] According to the present invention, preferably, the average pore size of the porous support layer is 30-60 nm (for example, it can be 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, or any two of the above values ​​within a range).

[0041] Preferably, the porosity of the porous support layer is 4-65%, more preferably 45-55% (for example, it can be 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, or any two of the above values ​​within a range).

[0042] Within the aforementioned range, it can be further ensured that the membrane with separation function can have high magnesium-lithium separation efficiency and water flux when used for magnesium-lithium separation.

[0043] This invention does not have special requirements for the materials of the substrate layer, porous support, and separation layer. However, preferably, the substrate layer is made of polyolefin (e.g., polyethylene nonwoven fabric).

[0044] According to the present invention, preferably, the film-forming polymer forming the porous support layer is selected from at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride, and polyaryl etherketone, with polyethersulfone and polysulfone being preferred; more preferably, the weight-average molecular weight of the film-forming polymer forming the porous support layer is 50,000-100,000 g / mol (for example, it can be 50,000 g / mol, 60,000 g / mol, 70,000 g / mol, 80,000 g / mol, 90,000 g / mol, or 100,000 g / mol).

[0045] According to the present invention, preferably, the film-forming polymer forming the separation layer is polyurea. The inventors of the present invention have further discovered in their research that, under the above conditions, the acid and alkali resistance of the membrane can be further guaranteed.

[0046] Fifthly, the present invention provides a method for preparing a membrane with separation function, the method comprising: introducing a modified lithium-ion sieve as described in the first or third aspect during the preparation of the membrane.

[0047] According to the present invention, preferably, the method further includes: sequentially preparing a porous support layer and a separation layer on a substrate layer, and introducing the modified lithium-ion sieve therein during the preparation of the porous support layer.

[0048] According to the present invention, preferably, the material of the substrate layer is selected from polyolefin.

[0049] According to the present invention, preferably, the film-forming polymer forming the porous support layer is selected from at least one of polyethersulfone, polysulfone, polyaryl ether, polybenzimidazole, polyetherketone, polyetheretherketone, polyacrylonitrile, polyvinylidene fluoride and polyaryl etherketone, preferably polyethersulfone and polysulfone; more preferably, the weight-average molecular weight of the film-forming polymer forming the porous support layer is 50,000 to 100,000 g / mol.

[0050] According to the present invention, preferably, the method further includes: preparing a porous support layer on a substrate layer using a dispersion containing a film-forming polymer for forming a porous support layer and a modified lithium-ion sieve. Thus, a membrane with a modified lithium-ion sieve loaded on a porous support layer can be prepared. The dispersant in the dispersion is not particularly limited, and can be, for example, N,N-dimethylformamide, N,N-dimethylacetamide, etc.

[0051] According to the present invention, preferably, the mass concentration of the film-forming polymer used to form the porous support layer in the dispersion is 10-25 wt%, more preferably 16-22 wt% (for example, it can be 16 wt%, 17 wt%, 18 wt%, 19 wt%, 20 wt%, 21 wt%, 22 wt%, and any two of the above values ​​within a range).

[0052] According to the present invention, preferably, the mass concentration of the modified lithium ion sieve in the dispersion is 0.0001-3 wt%, more preferably 0.05-2 wt% (for example, it can be 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 2 wt%, and any two of the above values ​​within the range and values ​​within the range).

[0053] According to the present invention, preferably, the mass concentration ratio of the film-forming polymer used to form the porous support layer and the modified lithium-ion sieve in the dispersion is (6-400):1, more preferably (100-360):1.

[0054] The film-forming polymer and modified lithium-ion sieve used to form the porous support layer can be dispersed in a dispersant, and then the resulting dispersion can be allowed to stand at 22-28°C for 2-4 hours to degas.

[0055] According to the present invention, a preferred method for preparing a porous support layer on a substrate layer includes: coating a dispersion (e.g., using a doctor blade) onto the substrate layer, and then immersing the substrate layer coated with the dispersion in water at 10-30°C for 10-60 minutes. It is understood that immersion can promote the formation of the porous support layer. The material can also be washed with water after immersion.

[0056] According to the present invention, preferably, the conditions for preparing the porous support layer on the substrate layer include having a thickness of 10-100 μm, more preferably 30-60 μm. As mentioned above, the average particle size of the modified lithium-ion sieve is generally low (preferably at the nanometer level) relative to the thickness of the porous support layer. Therefore, the presence of the modified lithium-ion sieve generally does not significantly affect the thickness of the porous support layer.

[0057] According to the present invention, preferably, relative to 1m 2 The substrate layer contains approximately 1-4000 mg of modified lithium-ion sieve, more preferably 60-1500 mg. The amount of dispersion can be adjusted to meet the above range.

[0058] According to the present invention, preferably, the separation layer is prepared by forming the separation layer on the surface of the porous support layer through interfacial polymerization.

[0059] Preferably, the conditions for preparing the separation layer include making the thickness of the separation layer 80-110 nm.

[0060] According to the present invention, preferably, the interfacial polymerization method includes: sequentially contacting the surface of the porous support layer with an aqueous solution containing a polyamine and an organic solution containing a polyisocyanate, followed by heat treatment. Through the above preparation method, a separation layer made of polyurea can be obtained.

[0061] Preferably, the polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine, and polyetheramine, more preferably polyethyleneimine and / or polyethylene polyamine.

[0062] According to the present invention, preferably, the mass concentration of the polyamine in the aqueous solution containing the polyamine is 0.1-10 wt%, more preferably 0.5-2.5 wt% (for example, it can be 0.5 wt%, 1 wt%, 1.5 wt%, 2.5 wt%, 2.5 wt%, and any two of the above values ​​within a range or range).

[0063] According to the present invention, preferably, the polyisocyanate is selected from at least one of isophthalic diisocyanate, isophorone diisocyanate, 1,6-hexanediisocyanate, toluene-2,6-diisocyanate, 1,4-phenyl diisocyanate and toluene-2,4-diisocyanate, more preferably 1,4-phenyl diisocyanate and / or 1,6-hexanediisocyanate.

[0064] According to the present invention, preferably, in the organic solution containing polyisocyanate, the mass concentration of polyisocyanate is 0.01-2 wt%, preferably 0.05-1 wt% (for example, it can be 0.05 wt%, 0.1 wt%, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1 wt%, and any two of the above values ​​within a range or range thereof).

[0065] According to the present invention, preferably, the mass ratio of the polyamine in the aqueous solution containing the polyamine to the mass of the polyisocyanate in the organic solution containing the polyisocyanate is (1-200):1, more preferably (5-50):1.

[0066] The total amount of polyamines in the aqueous solution containing polyamines, and the total amount of polyisocyanates in the solution containing polyisocyanates, are not particularly limited, as long as the formation of a polyurea separation layer on the support layer can be guaranteed. Generally, the amounts of both will be greater than the amounts that can participate in the reaction to form the polyurea separation layer. For example, relative to 400cm 2 The area of ​​the porous support layer, the amount of polyamine can be 5-500mg, and the amount of polyisocyanate can be 0.5-50mg.

[0067] According to the present invention, preferably, the contact time between the porous support layer and the aqueous solution containing polyamine is 5-100s, more preferably 10-60s.

[0068] According to the present invention, preferably, the contact time between the porous support layer and the organic phase containing polyisocyanate is 10-200s, more preferably 20-120s.

[0069] The contact between the porous support layer and the aqueous solution containing polyamines, as well as the contact between the porous support layer and the organic phase containing polyisocyanates, can be carried out at room temperature, such as at 23-26℃.

[0070] According to the present invention, preferably, the heat treatment temperature is 40-150°C, more preferably 50-120°C; the heat treatment time is 0.5-10 min, more preferably 1-5 min.

[0071] Once prepared, the membrane can be soaked in water for use.

[0072] In a sixth aspect, the present invention provides a membrane with separation function prepared by the method described in the fifth aspect.

[0073] The membrane with separation function prepared by the above method has high water flux and magnesium-lithium separation efficiency when applied to magnesium-lithium separation, and has good acid and alkali resistance, making it more suitable for practical applications.

[0074] In a seventh aspect, the present invention provides the application of a membrane with separation function as described in the fourth or sixth aspect in the separation of magnesium and lithium.

[0075] The present invention will be described in detail below through embodiments.

[0076] Before interfacial polymerization is carried out on the porous support layer, the average pore size and porosity of the porous support layer are measured using a pore size analyzer (model PSDA-20, purchased from Nanjing Gaoqian) (the preparation of the separation layer generally does not affect the already formed porous support layer).

[0077] Preparation Example 1

[0078] Li4Ti5O 12 Ball milling was performed for 12 hours in a ball mill to improve dispersibility. Then, polyvinyl alcohol (weight-average molecular weight 20,000 g / mol) and Li₄Ti₅O₂ were added. 12 The modified lithium-ion sieve (with an average particle size of 400 nm) was mixed in ultrapure water to achieve a polyvinyl alcohol concentration of 0.8 wt% and a lithium-ion sieve concentration of 0.8 wt%. The mixture was stirred at 30 °C for 150 min. The product was then centrifuged at room temperature and washed three times with pure water. It was then ball-milled at room temperature for 6 h and dried (8 h at 80 °C) to obtain modified lithium-ion sieve A.

[0079] Preparation Example 2

[0080] Li4Mn5O 12 Ball milling was performed for 12 hours in a ball mill to improve dispersibility. Then, polyvinyl alcohol (weight-average molecular weight 20,000 g / mol) and Li4Mn5O were added. 12 The modified lithium-ion sieve (with an average particle size of 500 nm) was mixed in ultrapure water to achieve a polyvinyl alcohol concentration of 1.2 wt% and a lithium-ion sieve concentration of 2.4 wt%. The mixture was stirred at 35 °C for 120 min. The product was then centrifuged at room temperature and washed three times with pure water. It was then ball-milled at room temperature for 6 h and dried (9 h at 90 °C) to obtain modified lithium-ion sieve B.

[0081] Preparation Example 3

[0082] The preparation was carried out in the same manner as in Example 1, except that the concentration of polyvinyl alcohol was 1.1 wt% and the concentration of lithium ion sieve was 0.5 wt%. Modified lithium ion sieve C was obtained.

[0083] Preparation Example 4

[0084] Li4Ti5O 12 Ball milling was performed for 12 hours in a ball mill to improve dispersibility. Then, polyvinyl alcohol (weight-average molecular weight 40,000 g / mol) and Li₄Ti₅O₂ were added. 12 The modified lithium-ion sieve (with an average particle size of 400 nm) was mixed in ultrapure water to achieve a polyvinyl alcohol concentration of 0.8 wt% and a lithium-ion sieve concentration of 0.8 wt%. The mixture was stirred at 30 °C for 150 min. The product was then centrifuged at room temperature and washed three times with pure water. It was then ball-milled at room temperature for 6 h and dried (8 h at 80 °C) to obtain the modified lithium-ion sieve D.

[0085] Preparation Example 5

[0086] Li4Ti5O 12 Ball milling was performed for 12 hours in a ball mill to improve dispersibility. Then, polyvinyl alcohol (weight-average molecular weight 20,000 g / mol) and Li₄Ti₅O₂ were added. 12 The modified lithium-ion sieve (with an average particle size of 400 nm) was mixed in ultrapure water to achieve a polyvinyl alcohol concentration of 4 wt% and a lithium-ion sieve concentration of 0.8 wt%. The mixture was stirred at 30 °C for 150 min. The product was then centrifuged at room temperature and washed three times with pure water. It was then ball-milled at room temperature for 6 h and dried (8 h at 80 °C) to obtain the modified lithium-ion sieve E.

[0087] Preparation Example 6

[0088] Similar to Preparation Example 1, except that polyvinyl alcohol was replaced with polyethylene glycol (weight-average molecular weight of 400 g / mol). Modified lithium-ion sieve F was obtained.

[0089] Example 1

[0090] A porous support layer casting solution with a polysulfone (weight-average molecular weight of 80,000 g / mol) concentration of 18 wt% and modified lithium-ion sieve A concentration of 0.05 wt% was prepared using N,N-dimethylformamide as a dispersant. The solution was degassed at 25°C for 120 min. Then, the casting solution was coated using a doctor blade (the volume of the coating solution was such that, relative to 1 m³...). 2 The substrate layer (approximately 60 mg of lithium ion sieve) was placed on a polyethylene nonwoven fabric (75 μm thick, 18 μm average pore size, and 21% porosity), and then immersed in water at 25°C for 60 min, followed by three water washes to form a porous support layer.

[0091] The upper surface of the porous support layer (with an area of ​​400 cm²) 2 The membrane was then exposed to an aqueous solution (50 ml) containing 0.5 wt% polyethyleneimine at 25°C for 60 seconds, after which the solution was drained. Next, the upper surface of the support layer was exposed to an Isopar E solution (30 ml) containing 0.1 wt% 1,3-phenyl diisocyanate at 25°C for 60 seconds, after which the solution was drained. Finally, the membrane was placed in an oven and heat-treated at 70°C for 5 minutes.

[0092] Example 2

[0093] The membrane was prepared according to the method of Example 1, except that the concentration of modified lithium-ion sieve A was 0.18 wt%.

[0094] Example 3

[0095] The membrane was prepared according to the method of Example 1, except that the concentration of modified lithium-ion sieve A was 0.1 wt%.

[0096] Example 4

[0097] The membrane was prepared according to the method of Example 1, except that the concentration of modified lithium-ion sieve A was 1.2 wt%.

[0098] Example 5

[0099] The membrane was prepared according to the method of Example 1, except that modified lithium-ion sieve A was replaced with modified lithium-ion sieve B.

[0100] Example 6

[0101] The membrane was prepared according to the method of Example 1, except that modified lithium-ion sieve A was replaced with modified lithium-ion sieve C.

[0102] Example 7

[0103] The membrane was prepared according to the method of Example 1, except that modified lithium-ion sieve A was replaced with modified lithium-ion sieve D.

[0104] Example 8

[0105] The membrane was prepared according to the method of Example 1, except that the concentration of polysulfone was 20 wt%.

[0106] Example 9

[0107] The membrane was prepared according to the method of Example 1, except that the modified lithium-ion sieve A was replaced with the modified lithium-ion sieve E.

[0108] Example 10

[0109] The membrane was prepared according to the method of Example 1, except that the concentration of modified lithium-ion sieve A was 3 wt%.

[0110] Example 11

[0111] A porous support layer casting solution with a polysulfone concentration of 20 wt% (weight average molecular weight of 100,000 g / mol) and a modified lithium-ion sieve A concentration of 0.15 wt% was prepared using N,N-dimethylformamide as a dispersant. The solution was degassed at 25°C for 120 min. Then, the casting solution was coated using a doctor blade (the coating amount was such that, relative to 1 m...). 2 The substrate layer (approximately 70 mg of lithium ion sieve) was placed on a polyethylene nonwoven fabric (85 μm thick, 15 μm average pore size, and 18% porosity), and then immersed in water at 24°C for 50 min, followed by three water washes to form a porous support layer.

[0112] The upper surface of the porous support layer (with an area of ​​400 cm²) 2 The membrane was then exposed to an aqueous solution (50 ml) containing 1.5 wt% polyethylene polyamine at 25 °C for 45 s, after which the solution was drained. Next, the upper surface of the support layer was exposed to an Isopar E solution (30 ml) containing 0.12 wt% 1,6-hexamethylene diisocyanate at 25 °C for 45 s, after which the solution was drained. Finally, the membrane was placed in an oven and heat-treated at 60 °C for 3 min.

[0113] Example 12

[0114] A porous support layer casting solution with a polysulfone (weight-average molecular weight of 80,000 g / mol) concentration of 19 wt% and modified lithium-ion sieve A concentration of 0.2 wt% was prepared using N,N-dimethylformamide as a dispersant. The solution was degassed at 25°C for 120 min. Then, the casting solution was coated using a doctor blade (the coating amount was such that, relative to 1 m...). 2 The substrate layer (approximately 50 mg of lithium ion sieve) was placed on a polyethylene nonwoven fabric (75 μm thick, 20 μm average pore size, and 25% porosity), and then immersed in water at 26°C for 45 min, followed by three water washes to form a porous support layer.

[0115] The upper surface of the porous support layer (with an area of ​​400 cm²) 2 The membrane was then exposed to an aqueous solution (50 ml) containing 1.0 wt% polyethyleneimine at 25°C for 50 seconds, after which the solution was drained. Next, the upper surface of the support layer was exposed to an Isopar E solution (30 ml) containing 0.08 wt% 1,3-phenyl diisocyanate at 25°C for 80 seconds, after which the solution was drained. Finally, the membrane was placed in an oven and heat-treated at 80°C for 4 minutes.

[0116] Comparative Example 1

[0117] The membrane was prepared according to the method of Example 1, except that the porous support layer casting solution did not contain modified lithium-ion sieve A.

[0118] Comparative Example 2

[0119] The membrane was prepared according to the method of Example 1, except that the modified lithium-ion sieve A was replaced with Li4Ti5O. 12 .

[0120] Comparative Example 3

[0121] The membrane was prepared according to the method of Example 1, except that the modified lithium-ion sieve A was replaced with the modified lithium-ion sieve F.

[0122] In Examples 2-10 and Comparative Examples 1-3, the volume of the casting solution coated was the same as in Example 1.

[0123] Test Example 1

[0124] Elemental analysis of the lithium-ion sieve before and after modification using XPS revealed changes in the C / O percentage, attributable to the polyvinyl alcohol coating layer. This indicates that a polyvinyl alcohol coating layer was indeed formed on the modified lithium-ion sieve.

[0125] The mass content of polyvinyl alcohol in the modified lithium-ion sieve (i.e., the mass content of polyvinyl alcohol in Table 1) was determined by the ratio of the weight gain after modification (i.e., the mass of polyvinyl alcohol) to the mass of the modified lithium-ion sieve.

[0126] The average particle size of the modified lithium-ion sieve was determined by transmission electron microscopy (TEM), and the average thickness of the polyvinyl alcohol was obtained by subtracting the average particle size of the lithium-ion sieve from the average particle size of the modified lithium-ion sieve.

[0127] Table 1

[0128]

[0129] Test Example 2

[0130] The following measurements were performed on the membranes prepared in the above embodiments and comparative examples:

[0131] The loading of the modified lithium-ion sieve relative to 1 g of membrane was determined by X-ray photoelectron spectroscopy (XPS) (i.e., the modified lithium-ion sieve loading in Table 2).

[0132] The thickness of the porous support layer and the separation layer was determined using scanning electron microscopy.

[0133] Table 2

[0134]

[0135]

[0136] Test Example 3

[0137] After soaking the membranes obtained in the above embodiments and comparative examples in water for 24 hours, the water flux and the desalination rate of magnesium chloride and lithium chloride were measured. The specific methods are as follows.

[0138] The membrane was placed in a membrane tank, and the water permeation rate of the membrane was measured over a certain period of time under conditions of 0.5 MPa and 25°C. The water flux was then calculated using the following formula:

[0139] J = Q / (A·t), where J is the water flux, Q is the water permeation rate (L), and A is the effective membrane area of ​​the composite nanofiltration membrane (m²). 2 ), where t is time (h);

[0140] (2) The desalination rate of the composite nanofiltration membrane was tested using the following method: The composite nanofiltration membrane was loaded into a membrane tank, and 2000 ppm magnesium chloride aqueous solution and 100 ppm lithium chloride aqueous solution were pre-pressurized at 0.5 MPa for 0.5 h. The permeate was then obtained at a pressure of 0.6 MPa. The concentrations of magnesium chloride and lithium chloride in the permeate were measured by ion chromatography, and the desalination rate was calculated using the following formula:

[0141] R = (Cp - Cf) / Cp × 100%, where R is the desalination rate, Cp is the concentration of magnesium chloride or lithium chloride in the original solution (measured by ion chromatography), and Cf is the concentration of magnesium chloride or lithium chloride in the permeate (measured by ion chromatography).

[0142] (3) The magnesium-lithium separation coefficient of the composite nanofiltration membrane was obtained by the following method: The composite nanofiltration membrane was loaded into the membrane tank. The original aqueous solution was a mixed aqueous solution of 2000 ppm magnesium chloride and 100 ppm lithium chloride. The aqueous solution was pre-pressurized at 0.5 MPa for 0.5 h, and then permeate was obtained at a pressure of 0.6 MPa. The concentrations of magnesium chloride and lithium chloride in the permeate were measured by ion chromatography, and the desalination rate was calculated by the following formula:

[0143] The lithium-magnesium separation coefficient is calculated using the following formula:

[0144]

[0145] Where S is the lithium-magnesium separation coefficient, and C Li，p and C Li，f The concentrations of lithium ions in the permeate and feed solution, respectively (measured by ion chromatography); C Mg，p and C Mg，f The concentrations of magnesium ions in the permeate and feed solution are respectively (measured by ion chromatography).

[0146] Table 3

[0147]

[0148] After immersing the membrane in a 20 wt% HCl aqueous solution for 480 h, the water flux and the desalination rate of magnesium chloride and lithium chloride were determined according to the method described above. The results are shown in Table 4.

[0149] Table 4

[0150]

[0151] As can be seen from the table above, compared with the comparative example, the lithium permeability and water flux of the embodiment are increased. The modified lithium-ion sieve in the porous support layer has pores that match the size of lithium ions. With the cooperation of the above layers, it can provide a specific channel for lithium ions, while magnesium ions cannot pass through. Under the pressure of the flowing water, lithium ions can specifically and rapidly permeate through the membrane, which improves the membrane's rejection rate for multivalent metal cations. At the same time, it allows lithium ions to pass through as quickly as possible, resulting in a large membrane flux and high magnesium-lithium separation efficiency.

[0152] Furthermore, the inventors of this invention also discovered that after acid immersion of the nanofiltration membrane for 480 hours, the XPS characterization of the modified lithium-ion sieve loading on the membranes prepared in Examples 1-12 showed a change within ±0.2%, which can be considered as the modified lithium-ion sieve not detaching. This indicates that the membrane provided by this invention has strong stability of the modified lithium-ion sieve loaded on the porous support layer, making it more suitable for practical use. In contrast, the XPS characterization of the lithium-ion sieve loading on the membrane prepared in Comparative Example 2 showed a change of 6 wt% (reduction).

[0153] Furthermore, as shown in Table 4, the membrane provided by this invention exhibits virtually no change in lithium ion permeability after immersion in 5wt% HCl for 480 hours, indicating that both the membrane and the polyurea separation layer on top of it possess strong acid and alkali resistance. This membrane can achieve the separation of monovalent lithium metal ions and high-valent metal ions (such as magnesium) under acidic conditions.

[0154] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified lithium ion-sieve, characterized by, The modified lithium ion sieve comprises a lithium ion sieve and polyvinyl alcohol coated on the lithium ion sieve, wherein the mass content of the polyvinyl alcohol is 0.5-5wt% relative to the mass of the modified lithium ion sieve; The weight average molecular weight of the polyvinyl alcohol is 20-40Kg / mol; The average particle size of the modified lithium ion sieve is 10nm-10μm.

2. The modified lithium ionic sieve of claim 1, wherein, The mass content of the polyvinyl alcohol is 0.9-2.5wt% relative to the total mass of the modified lithium ion sieve; And / or, the average thickness of the polyvinyl alcohol coated on the lithium ion sieve is 1-20nm.

3. The modified lithium ionic sieve of claim 1, wherein, The average thickness of the polyvinyl alcohol coated on the lithium ion sieve is 2-8nm; And / or, the average particle size of the modified lithium ion sieve is 20-520nm.

4. The modified lithium ionic sieve of claim 1 or 2, wherein, The lithium ion sieve is selected from lithium manganese oxide type lithium ion sieve and / or lithium titanium oxide type lithium ion sieve.

5. A method of preparing a modified lithium ion-sieve, characterized by, The method comprises: mixing polyvinyl alcohol and lithium ion sieve in solution state to obtain a modified lithium ion sieve, wherein the mass usage ratio of lithium ion sieve to polyvinyl alcohol is (0.3-5):1; The weight average molecular weight of the polyvinyl alcohol is 20-40Kg / mol; The average particle size of the lithium ion sieve is 10nm-10μm.

6. The method of claim 5, wherein, The mass usage ratio of polyvinyl alcohol to lithium ion sieve is (0.4-2):1; And / or, the mass concentration of polyvinyl alcohol in the solution is 0.1-5wt%; And / or, the mixing time is 2-4h and the mixing temperature is 20-40℃; And / or, the lithium ion sieve is selected from lithium manganese oxide type lithium ion sieve and / or lithium titanium oxide type lithium ion sieve; And / or, the method further comprises: solid-liquid separation of the mixed material, and drying of the obtained solid material.

7. The method of claim 5, wherein, The average particle size of the lithium ion sieve is 20-500nm.

8. The modified lithium ion sieve prepared by the method of any one of claims 5-7.

9. A membrane having a separation function, characterized by The membrane with separation function comprises a porous support layer, a separation layer, and the modified lithium ion sieve of any one of claims 1-3 and claim 8 further loaded on the porous support layer and / or the separation layer.

10. The membrane having a separation function according to claim 9, wherein, The loading amount of the modified lithium ion sieve is 1-100mg relative to 1g of the membrane; And / or, the membrane with separation function comprises a substrate layer, a porous support layer and a separation layer in sequence, and the modified lithium ion sieve is loaded on the porous support layer.

11. The membrane having a separation function according to claim 10, wherein, The loading amount of the modified lithium ion sieve is 3-15mg relative to 1g of the membrane.

12. The membrane having a separation function according to claim 10, wherein, The thickness of the substrate layer is 30-150μm; the average pore size is 10-25μm; and the porosity is 15-25%; And / or, the thickness of the porous support layer is 10-100μm; And / or, the thickness of the separation layer is 80-110nm; And / or, the average pore size of the porous support layer is 30-60nm; And / or, the porosity of the porous support layer is 4-65%.

13. The membrane having a separation function according to claim 12, wherein, The thickness of the substrate layer is 50-120μm; And / or, the thickness of the porous support layer is 30-60μm; And / or, the thickness of the separation layer is 85-95nm; And / or, the porosity of the porous support layer is 45-55%.

14. The membrane having a separation function according to claim 10 or 12, wherein, The material of the substrate layer is selected from polyolefin; And / or, the film-forming polymer forming the porous support layer is selected from at least one of polyether sulfone, polysulfone, polyarylether, polybenzimidazole, polyether ketone, polyether ether ketone, polyacrylonitrile, polyvinylidene fluoride and polyaryletherketone. And / or, the film-forming polymer forming the separation layer is polyurea.

15. The membrane having a separation function according to claim 14, wherein, The film-forming polymer forming the porous support layer is polyether sulfone and polysulfone.

16. The membrane having a separation function according to claim 14, wherein, The film-forming polymer forming the porous support layer has a weight average molecular weight of 50-100 million g / mol.

17. A method for producing a membrane having a separation function, characterized by, The method further comprises: introducing the modified lithium ion sieve in any one of claims 1-4 and claim 8 into the porous support layer during the preparation of the porous support layer.

18. The method of claim 17, wherein, The method further comprises: sequentially preparing the porous support layer and the separation layer on the substrate layer, and introducing the modified lithium ion sieve into the porous support layer during the preparation of the porous support layer. And / or, the material of the substrate layer is selected from polyolefin. And / or, the film-forming polymer forming the porous support layer is selected from at least one of polyether sulfone, polysulfone, polyarylether, polybenzimidazole, polyether ketone, polyether ether ketone, polyacrylonitrile, polyvinylidene fluoride and polyaryletherketone.

19. The method of claim 18, wherein, The film-forming polymer forming the porous support layer is polyether sulfone and polysulfone.

20. The method of claim 18, wherein, The film-forming polymer forming the porous support layer has a weight average molecular weight of 50-100 million g / mol.

21. The method of claim 18, wherein, The method further comprises: using a dispersion liquid containing the film-forming polymer for forming the porous support layer and the modified lithium ion sieve to prepare the porous support layer on the substrate layer.

22. The method of claim 21, wherein, In the dispersion liquid, the mass concentration of the film-forming polymer for forming the porous support layer is 10-25wt%.

23. The method of claim 22, wherein, In the dispersion liquid, the mass concentration of the film-forming polymer for forming the porous support layer is 16-22wt%.

24. The method of claim 21, wherein, In the dispersion liquid, the mass concentration of the modified lithium ion sieve is 0.0001-3wt%.

25. The method of claim 24, wherein, In the dispersion liquid, the mass concentration of the modified lithium ion sieve is 0.05-2wt%.

26. The method of claim 21, wherein, In the dispersion liquid, the mass concentration ratio of the film-forming polymer for forming the porous support layer and the modified lithium ion sieve is (6-400):

1.

27. The method of claim 26, wherein, In the dispersion liquid, the mass concentration ratio of the film-forming polymer for forming the porous support layer and the modified lithium ion sieve is (100-360):

1.

28. The method of claim 18, wherein, The method for preparing the porous support layer on the substrate layer comprises: coating the dispersion liquid on the substrate layer, and then immersing the substrate layer coated with the dispersion liquid in water at 10-30℃ for 10-60min.

29. The method of claim 18, wherein, The condition for preparing the porous support layer on the substrate layer comprises: making the thickness of the porous support layer be 10-100μm.

30. The method of claim 29, wherein, The condition for preparing the porous support layer on the substrate layer comprises: making the thickness of the porous support layer be 30-60μm.

31. The method of claim 18, wherein, The method for preparing the separation layer comprises: forming the separation layer on the surface of the porous support layer by interfacial polymerization.

32. The method of claim 31, wherein, The condition for preparing the separation layer comprises: making the thickness of the separation layer be 80-110nm.

33. The method of claim 31 or 32, wherein, The method for interfacial polymerization comprises: sequentially contacting the surface of the porous support layer with an aqueous solution containing a polyamine and an organic solution containing a polyisocyanate, and performing heat treatment.

34. The method of claim 33, wherein, The polyamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, o-phenylenediamine, 1,3,5-triaminobenzene, melamine, piperazine, diethylenetriamine, tetraethylenepentamine, polyethyleneimine and polyetheramine.

35. The method of claim 34, wherein, The polyamine is polyethyleneimine and / or polyethylene-polyamine.

36. The method of claim 33, wherein, The mass concentration of the polyamine in the aqueous solution containing the polyamine is 0.1-10 wt%.

37. The method of claim 36, wherein, The mass concentration of the polyamine in the aqueous solution containing the polyamine is 0.5-2.5 wt%.

38. The method of claim 33, wherein, The polyfunctional isocyanate is at least one selected from the group consisting of m-xylylene diisocyanate, isophorone diisocyanate, 1,6-hexane diisocyanate, toluene-2,6-diisocyanate, 1,4-phenylene diisocyanate and toluene-2,4-diisocyanate.

39. The method of claim 38, wherein, The polyfunctional isocyanate is 1,4-phenylene diisocyanate and / or 1,6-hexane diisocyanate.

40. The method of claim 36, wherein, The mass concentration of the polyfunctional isocyanate in the organic solution containing the polyfunctional isocyanate is 0.01-2 wt%.

41. The method of claim 40, wherein, The mass concentration of the polyfunctional isocyanate in the organic solution containing the polyfunctional isocyanate is 0.05-1 wt%.

42. The method of claim 33, wherein, The ratio of the mass of the polyamine in the aqueous solution containing the polyamine to the mass of the polyfunctional isocyanate in the organic solution containing the polyfunctional isocyanate is (1-200):

1.

43. The method of claim 42, wherein, The ratio of the mass of the polyamine in the aqueous solution containing the polyamine to the mass of the polyfunctional isocyanate in the organic solution containing the polyfunctional isocyanate is (5-50):

1.

44. The method of claim 33, wherein, The time for the porous support layer to contact the aqueous phase solution containing the polyamine is 5-100 s.

45. The method of claim 44, wherein, The time for the porous support layer to contact the aqueous phase solution containing the polyamine is 10-60 s.

46. The method of claim 33, wherein, The time for the porous support layer to contact the organic phase containing the polyfunctional isocyanate is 10-200 s.

47. The method of claim 46, wherein, The time for the porous support layer to contact the organic phase containing the polyfunctional isocyanate is 20-120 s.

48. The method of claim 33, wherein, The heat treatment temperature is 40-150℃; and the heat treatment time is 0.5-10 min.

49. The method of claim 48, wherein, The heat treatment temperature is 50-120℃; and the heat treatment time is 1-5 min.

50. The membrane with separation function prepared by the method of any one of claims 17-49.

51. The use of the membrane with separation function of any one of claims 9-16 and claim 50 in magnesium-lithium separation.

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