Modified nano molecular sieve / graphene oxide composite membrane for lithium-magnesium separation and preparation method of modified nano molecular sieve / graphene oxide composite membrane

Abstract

The invention relates to a modified nano molecular sieve / graphene oxide composite membrane for lithium-magnesium separation and a preparation method thereof, and the preparation method comprises the following steps: (1) stirring a nano molecular sieve and an amino modified solution at a certain temperature to react for a certain time, and centrifugally collecting an aminated nano molecular sieve, the preparation method comprises the following steps: ultrasonically mixing an aminated nano molecular sieve and graphene oxide in an aqueous solution, and then carrying out vacuum filtration on the surface of a porous base membrane to obtain the functionalized nano molecular sieve / graphene oxide composite membrane. The preparation method has the beneficial effect that the introduction of the nano molecular sieve into the graphene oxide membrane optimizes an interlayer channel. The aminated nano molecular sieve enhances the positively charged property of the composite membrane and enhances the selectivity of lithium and magnesium ions. The prepared modified nano molecular sieve / graphene oxide composite membrane is simple in preparation method and high in controllability, the pore channel effect and the charge repulsion effect of the composite membrane are enhanced through introduction of the aminated nano molecular sieve, and the modified nano molecular sieve / graphene oxide composite membrane has wide application prospects in lithium and magnesium ion separation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of separation membrane materials, and particularly relates to a method for separating lithium and magnesium in salt lake brine by using a modified nanomolecular sieve / graphene oxide composite membrane. BACKGROUND

[0002] The rapid development of the global new energy industry has significantly increased the demand for lithium resources. The main sources of lithium are salt lake brine and seawater, which often contain high concentrations of magnesium ions (Mg 2+ ), while lithium ions (Li + ) and magnesium ions have similar physical and chemical properties, which poses a great challenge to the separation and extraction of lithium. Therefore, developing efficient lithium-magnesium separation technology is of great significance for the extraction of lithium resources. With the continuous progress of membrane separation technology, membrane separation technology has become a new research direction for lithium-magnesium separation. Current researchers generally believe that the selective separation of lithium and magnesium ions by membrane materials mainly depends on the size and charge properties of lithium and magnesium ions. The existing commercial polyamide nanofiltration membranes have a wide pore size distribution range and poor structural uniformity / stability, making it difficult to achieve high-precision screening of lithium and magnesium ions and unable to meet the needs of practical applications.

[0003] Graphene oxide (GO) has a unique layered structure and abundant oxygen functional groups, which can be used to achieve selective separation of specific ions by adjusting the structure and surface chemical properties of the membrane. Graphene oxide membranes not only can screen different particles at the molecular or ionic level, but also have high mechanical strength and chemical stability. Therefore, they have great application potential in the field of lithium-magnesium separation. Based on the selective screening mechanism of lithium and magnesium ions, the separation performance of Mg 2+ / Li + can be improved by strengthening the size screening effect and charge repulsion. The strategy for strengthening the size screening effect is to insert nanomolecular sieves with different pore sizes between the graphene oxide layers to form graphene oxide membranes with a multi-level pore structure, thereby improving the screening precision of different sizes of hydrated ions in the composite membrane. For example, CN117123066A introduces small organic molecules as intercalation materials into graphene oxide membranes to achieve precise control of the interlayer spacing of graphene oxide membranes at the sub-nanometer level. The strategy for strengthening the charge repulsion effect is through amino-functionalized graphene oxide or amino-functionalized nanomolecular sieves. By introducing different amino-functionalization methods, different densities of amino groups are introduced into the membrane, and the positive charge density of the composite membrane is reasonably optimized to strengthen the cation rejection performance of the membrane, thereby improving the rejection of Mg 2+ . For example, patent CN105597577A introduces amino-functionalized MOFs into the polyamide separation layer to increase the positive charge density of the polyamide membrane

[0004] However, the practical application of graphene oxide membranes in lithium-magnesium separation still faces many challenges. The uniformity and stability of the structure of traditional intercalation materials are insufficient, resulting in insufficient ion selectivity of the composite membrane and performance degradation over time. Therefore, how to further improve the separation selectivity and structural stability of graphene oxide membranes has become a key technical problem to be solved

[0005] Therefore, in order to solve the above problems, the present application introduces charge-functionalized nanoscale molecular sieves (particle size < 100 nm) into the graphene oxide membrane. The nanoscale molecular sieves are functionalized by amino modification to enhance their positive charge density. The functionalized nanoscale molecular sieves / graphene oxide membrane is prepared by a pressure-assisted filtration method. The nanoscale molecular sieves with variable pore sizes precisely control the interlayer channels of graphene oxide, and the amino modification process enhances the positive charge density of the membrane, enhances the charge repulsion of the membrane, and enhances the ion selectivity and anti-fouling properties of the membrane. SUMMARY

[0006] The present application aims to overcome the structural defects of existing lithium-magnesium separation membranes and provides a simple and controllable method for preparing amino-functionalized nanoscale molecular sieves / graphene oxide membranes. The introduction of nanoscale molecular sieves can control the interlayer spacing of graphene oxide and enhance the structural stability of the membrane, thereby improving the permeation selectivity of the graphene oxide membrane. The amino modification process improves the positive charge density of the membrane, enhances the charge repulsion of the membrane, and improves the anti-fouling effect. The method has simple preparation steps, good repeatability, and good application prospects.

[0007] To achieve the above-mentioned purposes, the technical solutions of the present application are as follows:

[0008] A modified nanoscale molecular sieve / graphene oxide composite membrane for lithium-magnesium separation and a preparation method thereof, comprising the following steps:

[0009] (1) Prepare ultra-small nanoscale molecular sieves by hydrothermal crystallization method. The synthesized nanoscale molecular sieve material is ultrasonically treated under ice water bath, and dispersed by wet method to avoid aggregation, to obtain a nanoscale molecular sieve aqueous solution;

[0010] A certain amount of nanoscale molecular sieve solution is taken and added to a flask, then a certain amount of amino-modified solution is added, and stirred at a certain temperature for a certain time. After stirring, the amino-functionalized nanoscale molecular sieves are obtained by centrifugal separation;

[0011] (2) Aminated nano-molecular sieves were ultrasonically dispersed in an ice-water bath to obtain an aqueous solution of aminated nano-molecular sieves. A certain amount of monolayer graphene oxide nanosheets were dispersed in the aqueous solution and ultrasonically dispersed in an ice-water bath to obtain an aqueous solution of graphene oxide of a certain concentration. A certain amount of the aqueous solution of aminated nano-molecular sieves and a certain amount of graphene oxide solution were ultrasonically mixed for 1 hour to obtain a mixed solution. A porous membrane was fixed in a vacuum filtration device, and its surface was wetted with water. Then, the ultrasonically mixed solution was added to the surface of the membrane, and the membrane was filtered at 0.1 MPa to obtain an aminated nano-molecular sieve / graphene oxide composite membrane.

[0012] Preferably, the structure of the above-mentioned nanomolecular sieve is any one of the following topological structures: EMT type, FAU type, MFI type, BEA type, MWW type, CHA type, and BPH type.

[0013] Preferably, the above-mentioned amino-modified / grafted solution is any one of polydopamine solution, polyethyleneimine solution, amino-containing organosilane solution, diazonium salt modified solution, and ethylenediamine solution.

[0014] Preferably, the porous substrate membrane is any one of polyethersulfone microfiltration membrane, nylon microfiltration membrane, and polyacrylonitrile microfiltration membrane.

[0015] The nano-molecular sieve / graphene oxide composite membrane and its preparation method described in this invention are applied to lithium extraction and selective separation of lithium and magnesium from salt lake brine.

[0016] The advantages of this invention are as follows: Compared with the polyamide nanofiltration membranes currently widely studied for lithium-magnesium separation, it has the following advantages:

[0017] 1. Tunable pore structure, low ion transport resistance, and enhanced mechanical properties. Molecular sieves possess uniform pore size, and amination further controls the pore size, effectively blocking larger-diameter magnesium ions. Allowing smaller lithium ions Success. Furthermore, by inserting ultra-small nano-molecular sieves, the spacing between graphene oxide layers can be appropriately increased, simultaneously forming ion channel structures within the layers. These channels can be configured according to Li... + and Mg 2+ The size and surface charge of Li enable selective sieving, allowing Li to... + It is easier to pass through. In addition, the rigid molecular sieve intercalation structure improves the overall strength and compressive strength of the graphene oxide membrane, avoiding membrane deformation and pore blockage during long-term filtration operations.

[0018] 2. Enhanced charge repulsion and antifouling effects. The amino groups on the amination molecular sieve have a high affinity for lithium ions, which can enhance the attraction to Li-ions through electrostatic attraction and ion exchange. + The selective separation effect of Mg, while inhibiting the selective separation of Mg2+ The permeability is improved. Furthermore, amination of molecular sieves effectively reduces contaminant adhesion to the molecular sieve surface and graphene oxide film, enhancing the membrane's antifouling properties and facilitating cleaning and regeneration.

[0019] 3. The nano-molecular sieve / graphene oxide membrane prepared by this invention exhibits excellent lithium-magnesium separation performance. Ion permeation separation is used to separate the lithium content of the membrane. + / Mg 2+ Separation performance evaluation. The test feed solutions were 0.1 mol / L LiCl and MgCl2 solutions. The LiCl membrane prepared in this invention... + / Mg 2+ Selectivity is approximately 3-5. Lithium oxide films without added functionalized nanosieves in graphene oxide. + / Mg 2+ The selectivity was 1.21. Furthermore, the modified nano-molecular sieve / graphene oxide composite membrane exhibited good pressure resistance and mechanical stability. The functionalized nano-molecular sieve / graphene oxide membrane prepared by this invention possessed enhanced Li... + / Mg 2+ Its selectivity and structural stability make it highly valuable for application in specific scenarios.

[0020] The modified organic nanofiltration membrane obtained by the preparation method provided by this invention can be widely used in various fields such as environment, food, medicine, and chemical industry. Attached Figure Description

[0021] Figure 1 Scanning electron microscope image of the surface of the support film in Comparative Example 1 of this invention.

[0022] Figure 2 Cross-sectional scanning electron microscope image of the support membrane in Comparative Example 1 of this invention.

[0023] Figure 3 Scanning electron microscope image of the surface of the support membrane in Embodiment 2 of the present invention.

[0024] Figure 4 Cross-sectional scanning electron microscope image of the support membrane in Embodiment 2 of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, the present invention is not limited to the following embodiments. Any modifications that do not exceed the concept and scope of the present invention are within the protection scope of the present invention.

[0026] Materials and reagents required for composite membrane preparation:

[0027] Various nano-molecular sieves were prepared in the laboratory. Other reagents used included dopamine hydrochloride, tris(hydroxymethyl)aminomethane, polyethyleneimine (MW 1200-10000), ethylenediamine (Aladdin Reagent (Shanghai) Co., Ltd.), γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, sodium nitrite, lithium chloride, magnesium chloride hexahydrate (Sinopharm Chemical Reagent Co., Ltd.), anhydrous ethanol, toluene (Tianjin Fuyu Fine Chemical Co., Ltd.), p-phenylenediamine (TCI Reagent Co., Ltd., Japan), polyethersulfone microfiltration membrane (Haining Delv New Material Technology Co., Ltd.), nylon microfiltration membrane, and polyvinylidene fluoride microfiltration membrane (Yibo Filter Material Factory).

[0028] Example 1:

[0029] (1) 0.5 g of FAU-type nano-molecular sieve was added to 100 mL of a 100 mL aqueous solution of tris(hydroxymethyl)aminomethane and sonicated at room temperature for 1 h. 0.2 g of dopamine hydrochloride was added to the resulting solution and stirred at room temperature for 6 h to obtain a dopamine-modified FAU molecular sieve solution. The resulting solution was washed three times by centrifugation with deionized water at 10000 rpm for 15 min to obtain dopamine-modified FAU nano-molecular sieve. 0.5 g of dopamine-modified FAU nano-molecular sieve was dissolved in 10 mL of deionized water and sonicated for 1 h to obtain a dopamine-modified FAU nano-molecular sieve solution. 3 mg of graphene oxide was dispersed in 10 mL of deionized water and transferred to an ice-water bath for sonication for 1 hour. The two solutions were then mixed and sonicated for 1 h to obtain a dopamine-modified FAU nano-molecular sieve / graphene oxide mixed solution.

[0030] (2) Fix the polyethersulfone microfiltration membrane in a vacuum filtration device, then add 5 mL of deionized water to wet the membrane surface, and then remove the deionized water from the membrane surface by vacuum filtration; pour 20 mL of dopamine-modified FAU nano-molecular sieve / graphene oxide mixed solution obtained in step (1) onto the surface of the polyethersulfone microfiltration membrane, and then perform vacuum filtration at 0.1 MPa. After vacuum filtration, dopamine-modified FAU nano-molecular sieve / graphene oxide membrane is obtained, wherein the membrane thickness is 0.6-1.0 micrometers.

[0031] Example 2:

[0032] (1) Dissolve 0.5g of FAU nano-molecular sieve in 100mL of deionized water and sonicate in ice water for 2h to obtain FAU molecular sieve aqueous solution; dissolve 0.3g of polyethyleneimine with a molecular weight of 10000 in 20mL of deionized water and stir at room temperature for 6h to dissolve it. Then, mix the above FAU molecular sieve aqueous solution with the polyethyleneimine aqueous solution and stir for 3h. Then, centrifuge the above solution (10000rpm, 15min) to remove ungrafted polyethyleneimine and finally obtain polyethyleneimine modified FAU nano-molecular sieve.

[0033] (2) Dissolve 0.25 g of polyethyleneimine-modified FAU nanosieve in 10 mL of deionized water and sonicate in ice water for 2 h to obtain a uniformly dispersed polyethyleneimine-modified FAU nanosieve solution; disperse 3 mg of graphene oxide in 10 mL of deionized water and transfer to an ice water bath for sonication for 1 hour. Then mix the two solutions and sonicate for 1 h to obtain a polyethyleneimine-modified FAU nanosieve / graphene oxide mixed solution. Then fix the porous polyethersulfone microfiltration membrane in a vacuum filtration device, add 5 mL of deionized water to wet the membrane surface, and then remove the deionized water from the membrane surface by filtration; pour the above polyethyleneimine-modified FAU nanosieve / graphene oxide mixed solution onto the surface of the polyethersulfone microfiltration membrane and filter at 0.1 MPa. After the solution is removed by filtration, a polyethyleneimine-modified FAU nanosieve / graphene oxide composite membrane with a thickness of 0.6 μm is obtained on the polyethersulfone substrate membrane surface.

[0034] Example 3:

[0035] (1) Take 50 mL of toluene into a three-necked flask, then add 1 g of EMT nano-molecular sieve and stir to dissolve at room temperature. Then heat the above solution to 60 °C, and add 0.1 g of γ-aminopropyltriethoxysilane dropwise to modify the molecular sieve with aminosilane. Reflux at 60 °C for 6 h, then centrifuge and wash the above product with ethanol as the washing solution. The centrifugation conditions are 10000 rpm for 20 min. Collect the above product and label it as aminosilane modified EMT nano-molecular sieve.

[0036] (2) Dissolve 0.15 g of aminosilane-modified EMT nanomolecular sieve in 10 mL of deionized water and sonicate in ice water for 2 h to obtain uniformly dispersed aminosilane-modified EMT nanomolecular sieve; disperse 3 mg of graphene oxide in 10 mL of deionized water and transfer to an ice water bath for sonication for 1 hour. Then mix the two solutions and sonicate for 1 hour to obtain a mixed solution of aminosilane-modified EMT nanomolecular sieve. Then fix the porous nylon microfiltration membrane in a vacuum filtration device, add 5 mL of deionized water to wet the membrane surface, and then remove the deionized water from the membrane surface by filtration; pour the above aminosilane-modified EMT nanomolecular sieve onto the surface of the nylon microfiltration membrane and filter at 0.1 MPa. After the solution is removed by filtration, a polyethyleneimine-modified aminosilane-modified EMT nanomolecular sieve composite membrane is obtained on the surface of the polyethersulfone substrate membrane, wherein the membrane thickness is 1.0-2.0 micrometers.

[0037] Example 4:

[0038] (1) Take 0.6 g of MWW-type molecular sieve nanosheets into a 100 mL Erlenmeyer flask, add 30 mL of laboratory-made sulfonated polyaniline solution, stir at room temperature for 3 h, wash with deionized water by centrifugation at 12000 rpm for 15 min, collect the product after centrifugation and label it as polyaniline-modified MWW molecular sieve nanosheets; take 0.2 g of polyaniline-modified MWW molecular sieve nanosheets and dissolve them in 10 mL of deionized water, sonicate for 1 h to obtain a polyaniline-modified MWW molecular sieve nanosheet dispersion solution; take 3 mg of graphene oxide and disperse it in 10 mL of deionized water, transfer it to an ice-water bath and sonicate for 1 h to disperse it. Then mix the above two solutions and sonicate for 1 h to obtain a polyaniline-modified MWW molecular sieve nanosheet / graphene oxide mixed solution.

[0039] (2) Fix the polyethersulfone microfiltration membrane in a vacuum filtration device, then add 5 mL of deionized water to wet the membrane surface, and then remove the deionized water from the membrane surface by filtration; pour 20 mL of polyaniline-modified MWW molecular sieve nanosheets / graphene oxide mixed solution obtained in step (1) onto the surface of the polyethersulfone microfiltration membrane, and then perform filtration at 0.1 MPa. After filtration, a polyaniline-modified MWW molecular sieve nanosheets / graphene oxide membrane is obtained, wherein the membrane thickness is about 1.0 micrometers.

[0040] Example 5:

[0041] The preparation of dopamine-modified FAU nanosieve / graphene oxide membranes was carried out according to the method in Example 1, except that MFI molecular sieve nanosheets were used instead of FAU nanosieves. The thickness of the prepared dopamine-modified MFI molecular sieve nanosheet / graphene oxide membrane was 1.0-1.5 micrometers.

[0042] Example 6:

[0043] The preparation of the polyethyleneimine-modified FAU nanosieve / graphene oxide composite membrane was carried out according to the method of Example 2, except that BPH molecular sieve nanosheets were used instead of nano-FAU molecular sieves. The thickness of the obtained polyethyleneimine-modified BPH molecular sieve nanosheet / graphene oxide composite membrane was 1.0-2.0 micrometers.

[0044] Example 7:

[0045] The preparation of polyaniline-modified MWW molecular sieve nanosheets / graphene oxide films was carried out according to the method in Example 4, except that EMT nanomolecular sieves were used instead of MWW molecular sieve nanosheets. The thickness of the obtained polyaniline-modified EMT nanomolecular sieve / graphene oxide film was 1.0-1.5 micrometers.

[0046] Comparative Example 1:

[0047] (1) Take 3 mg of graphene oxide and disperse it in 10 mL of deionized water. Transfer it to an ice-water bath and sonicate for 1 hour to disperse it. Then mix the two solutions and sonicate for 1 hour to obtain a graphene oxide solution.

[0048] (2) Fix the polyethersulfone microfiltration membrane in a vacuum filtration device, then add 5 mL of deionized water to wet the membrane surface, and then remove the deionized water from the membrane surface by filtration; pour the graphene oxide solution obtained in step (1) onto the surface of the polyethersulfone microfiltration membrane, and then perform filtration at 0.1 MPa. After filtration, a graphene oxide membrane is obtained, wherein the membrane thickness is 0.4-0.6 micrometers.

[0049] The membranes prepared in Examples 1, 2 and Comparative Example 1 were tested for lithium-magnesium ion permeation separation performance.

[0050] Ion permeability (P) i ,mol m -2 h -1 The calculation formula is as follows:

[0051] P i =(C i ×V) / (A×△t)

[0052] Where Ci represents the permeate ion concentration, V represents the permeate ion volume (L), and A represents the effective membrane area (m²). -2 ), where Δt represents the ion permeation time (h).

[0053] The formula for calculating ion selectivity (S) is as follows:

[0054] S = P i1 / P i2

[0055] Among them, P i1 and P i2 They are Li + and Mg 2+ Ion permeability

[0056] The test results are shown in the table below:

[0057]

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified nano-molecular sieve / graphene oxide composite membrane for lithium-magnesium separation and its preparation method, comprising the following steps: (1) The aqueous solution of nano-molecular sieve and the amino-modified solution were stirred at a certain temperature (20℃~80℃) for a certain time (0.5h~12h), and the solid product was collected by centrifugation and washed (centrifugation speed of 8000rpm~15000rpm, centrifugation time of 10min~20min) to obtain amino-modified nano-molecular sieve. A certain amount (0.1~1.0g) of amino-modified nano-molecular sieve was dispersed in an aqueous solution, and then mixed with an aqueous solution of graphene oxide of a certain concentration (the concentration of graphene oxide in the solution is 0.2wt%~0.5wt%) to obtain an amino-modified nano-molecular sieve / graphene oxide mixed solution; (2) Fix the porous bottom membrane in a vacuum filtration device, wet it with water, and then add a certain amount of amino-modified nano-molecular sieve / graphene oxide mixed solution to the membrane surface. Vacuum filter the membrane under a certain pressure (filtration pressure less than 0.15MPa). After filtration is completed, an amino-modified nano-molecular sieve / graphene oxide composite membrane is obtained on the surface of the porous bottom membrane.

2. The modified nano-molecular sieve / graphene oxide composite membrane for lithium-magnesium separation and its preparation method according to claim 1, characterized in that, The nanomolecular sieve topology type mentioned in step (1) is one of EMT type, FAU type, MFI type, BEA type, MWW type, CHA type, and BPH type.

3. The modified nanomolecular sieve / graphene oxide composite membrane for lithium-magnesium separation and its preparation method according to claim 1, characterized in that, The amino-modified solution mentioned in step (1) is any one of polydopamine aqueous solution, polyethyleneimine aqueous solution, amino-containing organosilane solution, diazonium salt solution, and ethylenediamine solution.

4. The modified nanomolecular sieve / graphene oxide composite membrane for lithium-magnesium separation and its preparation method according to claim 1, characterized in that, The mass ratio of amino-modified nanomolecular sieves and graphene oxide in the mixed solution in step (2) is 1 / 20 to 1 / 2.

5. The modified nanomolecular sieve / graphene oxide composite membrane for lithium-magnesium separation and its preparation method according to claim 1, characterized in that, The porous bottom membrane mentioned in step (2) is at least one of polyethersulfone microfiltration membrane, nylon microfiltration membrane, and polyacrylonitrile microfiltration membrane.

6. The modified nanomolecular sieve / graphene oxide composite membrane for lithium-magnesium separation and its preparation method according to claim 1, characterized in that, The modified nano-molecular sieve / graphene oxide membrane described in step (2) is prepared using a vacuum filtration device with a filtration pressure of less than 0.15 MPa.

7. The modified nanomolecular sieve / graphene oxide composite membrane for lithium-magnesium separation and its preparation method according to claim 1, characterized in that, The nanomolecular sieve / graphene oxide composite membrane has a smooth planar structure and a uniform membrane thickness of 0.5 micrometers to 4 micrometers.

8. The beneficial effects of the present invention compared with the prior art: (1) This invention introduces nano-molecular sieves with high porosity and specific pore structure into the graphene oxide membrane, and expands the interlayer channels of graphene oxide by modifying the nano-molecular sieves with amino functionalization, thereby enhancing the mechanical stability of the membrane. Compared with the traditional process of preparing polyamide membranes by interfacial polymerization, the preparation process of functionalized nano-molecular sieves / graphene oxide membranes is simple and highly controllable. (2) Aminofunctionalized nano-molecular sieves improve the charge properties of nano-molecular sieves, enhance the positive charge of graphene oxide composite membranes, strengthen the membrane's repulsion of positively charged ions, and enhance the anti-fouling effect of composite membranes.

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