Method for in-situ preparation of DABSA sulfonated modified composite nanofiltration membrane through interfacial polymerization

Abstract

The invention discloses a method for in-situ preparation of a DABSA sulfonation modified composite nanofiltration membrane through interfacial polymerization, and belongs to the field of lithium extraction of salt lakes with high magnesium-lithium ratio. Comprising the following steps: preparing a DABSA water-phase monomer solution, adding a phase transfer catalyst into the DABSA solution, and adjusting the pH value of the solution to be alkaline; preparing an organic phase monomer and dissolving in an organic solution; immersing the DABSA solution into the surface of a commercial polymer composite membrane by using an interfacial polymerization method, and then immersing the organic phase solution into the surface of the commercial polymer composite membrane to prepare a primary layer of a DABSA sulfonation modified composite nanofiltration membrane; and further performing thermal crosslinking on the primary layer of the composite nanofiltration membrane by using a blast oven to obtain the DABSA sulfonated composite nanofiltration membrane. The membrane can be used for a pretreatment process of extracting lithium from a salt lake with a high magnesium-lithium ratio, and the purpose of preliminarily reducing the magnesium-lithium ratio is achieved through the mass transfer promotion effect of the nanofiltration membrane on Mg < 2 + >, so that the energy consumption in the lithium extraction process is reduced.

Description

Technical Field

[0001] The present invention relates to a method for preparing a sulfonated modified composite nanofiltration membrane PA-DABSA by synergistically combining interfacial polymerization technology and in-situ growth. This type of membrane can be used in the pretreatment process of extracting lithium from salt lakes with a high magnesium-lithium ratio. Through the mass transfer promotion effect of the nanofiltration membrane on Mg 2+ , the energy consumption in the lithium extraction process is reduced, thereby reducing the cost of lithium extraction from salt lakes, and belongs to the field of lithium extraction from salt lakes. Background Art

[0002] Salt lake brine, as an important lithium resource reserve, accounts for approximately 60% of the total global lithium resources, which makes the technology of extracting lithium from salt lakes gradually become an important direction for lithium resource development. Among many extraction methods, compared with traditional extraction methods and electrodialysis methods, nanofiltration membrane technology exhibits significant advantages of high efficiency, energy conservation, and environmental friendliness, and has become one of the key technologies for lithium extraction from salt lakes [Liu M, Wei M, Liu G, et al. Journal of Membrane Science, 2024, 712: 123247; Ying Y, Ying W, Li Q, et al. Applied Materials Today, 2017, 7: 144 - 158.]. However, the coexistence of lithium and magnesium ions commonly present in salt lake resources, as well as a relatively high magnesium-lithium ratio (usually ranging from dozens to thousands) [Liu Y, Li Q, Wang S, et al. Separation and Purification Technology, 2023, 308: 122968.], pose great challenges to directly extracting lithium from brine solely relying on a lithium-selective permeable membrane.

[0003] In recent years, the adsorption-membrane separation coupling process has gradually become the mainstream technology for treating salt lake brine with a high magnesium-lithium ratio. This process selectively extracts lithium ions in the adsorption section, concentrates the lithium ions through elution (i.e., reduces the magnesium-lithium ratio), and finally completes purification through the separation of a lithium-selective permeable membrane. However, the adsorption process section has problems such as a large amount of adsorbent used and high energy consumption, significantly increasing the overall cost of lithium extraction from salt lakes [Butt F, Lewis A, Chen T, et al. Membranes, 2022, 12(4), 373.]. Against this background, developing a magnesium-selective permeable separation membrane can effectively alleviate the usage of adsorption columns, and through the dual-membrane coupling process of the magnesium-selective permeable membrane and the lithium-selective permeable membrane, it is expected to achieve low energy consumption in the lithium extraction process from salt lakes, thereby reducing the lithium extraction cost. Therefore, developing a magnesium-selective permeable nanofiltration membrane has important research value and application prospects. However, through literature research, it is found that there is currently no report on the research of magnesium-selective permeable membranes.

[0004] The ion separation mechanism of nanofiltration membranes mainly includes size sieving and Donnan effect. Due to the larger hydrated radius of magnesium ions, it is impossible to achieve preferential permeation of magnesium ions by relying on size sieving. In current research, most highly negatively charged nanofiltration membranes show a higher permeation rate of MgCl2 than NaCl during the Mg 2+ / Na + separation process. By strengthening the negative charge density of the separation layer of the nanofiltration membrane [Zhu Y, Dou P, He H, et al. Separation and Purification Technology, 2020, 239: 116528; Al-Nahari A, Li S, Su B, et al. Separation and Purification Technology, 2022, 291: 120947.], the adsorption and transport of magnesium ions are promoted. The experimental results show that MgCl2 exhibits better permeability than NaCl, confirming the practical feasibility of the strong negative charge property for the preferential permeation of magnesium ions. However, the magnesium / sodium selectivity of this system is still low. The main reason is that although the high charge density property of the sulfonic acid groups on the surface of the nanofiltration membrane separation layer gives it an advantage in preferentially adsorbing magnesium ions, the discontinuous distribution of negatively charged functional groups in the mass transfer channels inside the membrane cannot promote the rapid transport of magnesium ions. Therefore, developing a nanofiltration membrane separation layer with continuous strong negative charge property is an effective way to achieve a nanofiltration membrane with preferential magnesium permeation.

[0005] The pore diameter of the traditional nanofiltration membrane prepared from piperazine and 1,3,5-benzenetricarbonyl chloride is usually about 0.5 nm [Zhu Q, Xu Z, Fu J, et al. Desalination, 2023, 558, 116623.], while the hydrated radius of Mg 2+ is about 0.43 nm. It is impossible to achieve preferential transport of Mg 2+ only by pore size sieving. Moreover, the separation layer of this nanofiltration membrane is positively charged, and it is difficult to achieve preferential transport of Mg 2+ according to the Donnan effect. In recent years, researchers have strengthened the separation layer charge and membrane pore size by selecting sulfonated amine monomers to enhance the separation of Mg 2+The promoting mass transfer effect. 2,5-Diaminobenzenesulfonic acid (DABSA) is a common polymer material. Due to the presence of both amino reactive sites and sulfonic acid functional groups in its molecular structure, it is widely used in the preparation of separation membranes and all has relatively excellent separation performance [Liu X, Wang J, Shang Y, et al. Journal of the American Chemical Society, 2024, 146: 2313-2318; Wei X, Gan Z, Shen Y, et al. Journal of Colloid and Interface Science, 2019, 553: 475-483.]. Interfacial polymerization technology is an effective method for preparing composite nanofiltration membranes [Zhang X, Zhang H, Wang L, et al. Desalination, 2024, 578: 117422; Zhang H, Chen Y, Tang S, et al. Journal of Membrane Science, 2022, 664: 121070.]. Therefore, in this invention, a negatively charged continuous sulfonated (DABSA) modified composite nanofiltration membrane is prepared through the synergistic effect of interfacial polymerization technology and in-situ growth approach. By this method, the mass transfer rate of the nanofiltration membrane to Mg 2+ is effectively increased, while maintaining the high rejection characteristics for Li + . The preparation process is simple and has good repeatability. Through charge continuity regulation and mass transfer path optimization, a new strategy is proposed for the pretreatment link of extracting lithium from high magnesium-lithium ratio salt lakes. Summary of the Invention

[0006] The purpose of this invention is to construct a sulfonated modified composite nanofiltration membrane with preferential transport of Mg 2+ through the synergistic effect of interfacial polymerization technology and in-situ growth. The separation layer of this composite membrane has continuous negatively charged mass transfer channels and can specifically preferentially transport Mg 2+ . The prepared composite membrane is applied to the pretreatment process of extracting lithium from high magnesium-lithium ratio salt lakes in the field of nanofiltration separation, and has good preferential Mg 2+ transport performance and stability.

[0007] This method includes the following steps:

[0008] (1) Pretreat the polymer composite substrate membrane to remove organic matter, inorganic matter and microorganisms on the surface of the substrate membrane;

[0009] (2) Disperse the sulfonated amine monomer in deionized water, add a certain amount of phase transfer catalyst to the solution, and then adjust the pH of the solution to alkaline such as 10, and use ultrasonic method to prepare a uniform aqueous solution;

[0010] (3) Dissolve a certain amount of organic phase monomers in an organic solvent to prepare a homogeneous organic phase solution, and ultrasonic treatment can be further utilized;

[0011] (4) By means of interfacial polymerization, immerse the aqueous solution in the surface of the porous substrate membrane, and then remove the excess aqueous solution with a rubber roller after a certain time;

[0012] (5) After the completion of (4), immerse a certain amount of the organic phase solution in the surface of the porous substrate membrane, pour out the excess organic phase solution after a certain time, and prepare the primary layer of the sulfonated modified composite nanofiltration membrane;

[0013] (6) Put the composite membrane obtained in (5) into a forced-air oven for heat treatment for a certain time. Obtain the 2,5-diaminobenzenesulfonic acid-based sulfonated modified (DABSA) composite nanofiltration membrane;

[0014] In the present invention, the substrate for preparing the sulfonated modified composite nanofiltration membrane can be a commercially available polymer composite nanofiltration membrane, and the membrane material is aromatic polyamide, poly(piperazine amide), sulfonated polysulfone, polyurea, polyether, poly(dienol) / poly(piperazine amide) mixture, and the pore size of the porous membrane is about 1.0 nm.

[0015] In step (2), the sulfonated amine monomer of the aqueous phase monomer for interfacial polymerization is selected from 2,5-diaminobenzenesulfonic acid (DABSA), and the mass percentage concentration in the aqueous solution is 0.3 - 0.9%, and the mass percentage concentration of the phase transfer catalyst CTAB is 0.012 - 0.036%.

[0016] In step (3), the organic phase monomers: 1,3,5-benzenetricarbonyl chloride, terephthaloyl chloride, cyanuric chloride, toluene diisocyanate, isophthaloyl chloride, hexamethylene diisocyanate. The mass percentage concentration is 0.08 - 0.15%, preferably 0.1%.

[0017] Organic solvents: n-hexane, cyclopentyl methyl ether, toluene, dichloromethane, cyclopentane, xylene, chloroform.

[0018] In step (4), the time for the aqueous solution to immerse the polymer composite membrane is 4 - 8 min, preferably 5 min.

[0019] In step (5), the time for the organic phase solution to immerse the polymer composite membrane is 0.8 - 1.2 min, preferably 1 min.

[0020] In steps (4) and (5), the reaction temperature is 15 - 45 °C, preferably 25 °C, and the reaction humidity is 20 - 30% RH, preferably 21% RH.

[0021] The present invention is used as a nanofiltration membrane in the pretreatment process of extracting lithium from high magnesium-lithium salt lakes (magnesium-lithium molar ratio greater than or equal to 1:1), and through the nanofiltration membrane for Mg 2+The mass transfer promotion effect is used to achieve the purpose of initially reducing the magnesium-lithium ratio in the salt lake.

[0022] The principle of the technical solution of the present invention is as follows: By using the method of interfacial polymerization, since the amino group (-NH2) has strong nucleophilicity, it will attack the carbonyl carbon atom in the acyl chloride group (-COCl) to undergo a nucleophilic substitution reaction to form an amide bond (-CONH-) while releasing a by-product of hydrogen chloride (HCl). After the by-product is generated, it will be quickly neutralized by the base in the aqueous phase to form a sulfonated polyamide membrane. Or the amino group (-NH2) attacks the isocyanate group (-NCO) to react to form a sulfonated polyurea membrane. In addition, the sulfonic acid group is enriched on the surface of the separation layer, making the crosslinked separation layer network carry negative charges, which can effectively 2+ undergo the Donnan effect with Mg 2+ greatly promoting the transport of Mg + in the separation layer. At the same time, the interaction force between the sulfonic acid group and Li + is weak and is retained on the upstream side of the membrane, so that Mg 2+ is filtered with the solution while Li + and Na + are retained (that is, preferential Mg 2+ transport), achieving the effect of magnesium-lithium separation.

[0023] Technical advantages

[0024] The present invention prepares a sulfonated modified composite nanofiltration membrane with a negatively charged through-structure by interfacial polymerization technology. This unique negatively charged through-structure can effectively promote the selective transport of Mg 2+ in the mass transfer channel, improve the membrane structure stability and permeation flux while maintaining the rejection rate of Li + ; this method is a typical sulfonated modified composite membrane preparation technology, which is simple in operation and stable in structure, and has the potential for industrial promotion. The sulfonated modified composite nanofiltration membrane prepared by this technology is used to separate a 1g / L sodium sulfate aqueous solution system, a 1g / L magnesium chloride aqueous solution system, and a 1g / L lithium chloride solution system. When the operating pressure is 0.4 MPa, the fluxes are 6.66 L / m 2 h bar, 7.37 L / m 2 h bar and 6.59 L / m 2 h bar respectively; the rejection rates are 97.3%, 53.59% and 81.5% in sequence. Description of the drawings

[0025] Figure 1 It is a scanning electron microscope image of the cross-section of the DABSA sulfonated composite nanofiltration membrane treated by interfacial polymerization in Example 1.

[0026] Figure 2 It is a scanning electron microscope image of the surface of the DABSA sulfonated composite nanofiltration membrane in Example 1. Detailed implementation mode

[0027] The present invention will be described in detail below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0028] The DABSA sulfonated composite nanofiltration membrane prepared by using this technology is used to separate 1 g / L aqueous sodium sulfate solution system, 1 g / L aqueous magnesium chloride solution system, and 1 g / L lithium chloride solution system.

[0029] Example 1

[0030] A commercial polymer composite nanofiltration membrane is used, mostly polysulfone ultrafiltration membrane material, with a membrane pore size of 0.001–0.1 μm and a membrane area of 22.05 cm 2 , and the aqueous DABSA concentration is 0.7 wt%.

[0031] Preparation method of DABSA sulfonated composite nanofiltration membrane

[0032] (1) A polysulfone ultrafiltration membrane about 5 cm long is rinsed and pretreated with deionized water to remove organic substances, inorganic substances and microorganisms on its surface, and then the deionized water is replaced and stored until use;

[0033] (2) 0.7 wt% of DABSA monomer is dispersed in deionized water, 0.028 wt% of CTAB phase transfer catalyst is added to the solution, and the pH of the solution is adjusted to 10 with NaOH. An evenly mixed aqueous solution is prepared by ultrasonic method;

[0034] (3) 0.1 wt% of 1,3,5-benzenetricarbonyl chloride monomer is dissolved in n-hexane organic solvent, and an evenly mixed organic solution is prepared by ultrasonic method;

[0035] (4) By means of interfacial polymerization, the temperature of the constant temperature and humidity chamber is set at 15 - 40 °C, preferably 25 °C, and the humidity is the reaction humidity of 20 - 35% RH, preferably 21% RH. The aqueous solution is immersed on the surface of the porous substrate membrane, and after reacting for 5 minutes, the excess aqueous solution is removed with a rubber roller;

[0036] (5) After (4) is completed, the organic solution is immersed on the surface of the porous substrate membrane, and after reacting for 1 minute, the excess organic solution is poured out to prepare the primary layer of the sulfonated composite nanofiltration membrane.

[0037] (6) The composite membrane obtained in (5) is put into a blast drying oven for heat treatment at 60 °C for 10 minutes. A 2,5-diaminobenzenesulfonic acid (PA-DABSA) composite nanofiltration membrane is obtained.

[0038] (7) The above-prepared PA-DABSA composite nanofiltration membrane is soaked in deionized water for storage.

[0039] When the operating pressure is 0.4 MPa, the rejection rate and flux of sodium sulfate are 97.3% and 6.66 L / m 2 h bar respectively; for another parallel test: the rejection rate and flux of sodium sulfate are 99.73% and 6.72 L / m 2 h bar respectively.

[0040] When the operating pressure is 0.4 MPa, the rejection rate and flux of magnesium chloride are 53.59% and 7.37 L / m 2 h bar respectively. For another parallel test: the rejection rate and flux of magnesium chloride are 43.71% and 8.39 L / m 2 h bar respectively.

[0041] When the operating pressure is 0.4 MPa, the rejection rate and flux of lithium chloride are 81.5% and 6.59 L / m 2 h bar respectively.

[0042] Example 2

[0043] A commercial polymer composite nanofiltration membrane is used, mostly poly(piperazine amide) membrane material, with a membrane pore size of 0.5–1.0 nm and a membrane area of 10.8 cm 2 , and the aqueous phase concentration of DABSA is 0.7 wt%.

[0044] Preparation method of DABSA sulfonated composite nanofiltration membrane

[0045] (1) A poly(piperazine amide) membrane about 7 cm long is rinsed and pretreated with deionized water to remove organic substances, inorganic substances and microorganisms on its surface, and then the deionized water is replaced and stored until use;

[0046] (2) 0.7 wt% of DABSA monomer is dispersed in deionized water, 0.028 wt% of CTAB phase transfer catalyst is added to the solution, and the pH of the solution is adjusted to 10 with NaOH. An evenly mixed aqueous phase solution is prepared by ultrasonic means;

[0047] (3) 0.1 wt% of 1,3,5-benzenetricarbonyl chloride monomer is dissolved in n-hexane organic solvent n-hexane, and an evenly mixed organic phase solution is prepared by ultrasonic means;

[0048] (4) By means of interfacial polymerization, the temperature of the constant temperature and humidity chamber is set to 20-40 °C, preferably 25 °C, and the reaction humidity is 20-30% RH, preferably 21% RH. The aqueous phase solution is immersed on the surface of the porous substrate membrane, and after reacting for 5 min, the excess aqueous phase solution is removed with a rubber roller;

[0049] (5) After (4) is completed, immerse the organic phase solution on the surface of the porous substrate membrane. After reacting for 1 min, pour out the excess organic phase solution to prepare the primary layer of the sulfonated composite nanofiltration membrane.

[0050] (6) Put the composite membrane obtained in (5) into a forced-air oven for heat treatment at 60 °C for 10 min to obtain the 2,5-diaminobenzenesulfonic acid (PA-DABSA) composite nanofiltration membrane. (7) Immerse the above-prepared PA-DABSA composite nanofiltration membrane in deionized water for storage. When the operating pressure is 0.4 MPa, the rejection rate and flux of sodium sulfate are 98.5% and 7.63 L / m 2 h bar, respectively; when the operating pressure is 0.4 MPa, the rejection rate of magnesium chloride is 45.69%; when the operating pressure is 0.4 MPa, the rejection rate of lithium chloride is 80.3%.

[0051] Example 3

[0052] Use a commercial polymer composite nanofiltration membrane, mostly polyurea membrane material, with a membrane pore size of 0.5–2 nm and a membrane area of 15.78 cm 2 , and the aqueous phase concentration of DABSA is 0.7 wt%.

[0053] Preparation method of DABSA sulfonated composite nanofiltration membrane

[0054] (1) Rinse and pre-treat a polyurea membrane about 5 cm long with deionized water to remove organic substances, inorganic substances, and microorganisms on its surface. Then replace the deionized water and store it until use.

[0055] (2) Disperse 0.7 wt% of DABSA monomer in deionized water, add 0.028 wt% of CTAB phase transfer catalyst to the solution, and adjust the pH of the solution to 10 using NaOH. Use ultrasonic method to prepare a homogeneous aqueous phase solution.

[0056] (3) Dissolve 0.1 wt% of 1,3,5-benzenetricarbonyl chloride monomer in n-hexane organic solvent n-hexane, and use ultrasonic method to prepare a homogeneous organic phase solution.

[0057] (4) By means of interfacial polymerization, set the temperature of the constant temperature and humidity box to 15-45 °C, preferably 25 °C, and the reaction humidity to 20-35% RH, preferably 21% RH. Immerse the aqueous phase solution on the surface of the porous substrate membrane, and after reacting for 5 min, use a rubber roller to remove the excess aqueous phase solution.

[0058] (5) After (4) is completed, immerse the organic phase solution on the surface of the porous substrate membrane. After reacting for 1 min, pour out the excess organic phase solution to prepare the primary layer of the sulfonated composite nanofiltration membrane.

[0059] (6) Place the composite membrane obtained in (5) into a forced-air oven for heat treatment at 60 °C for 10 min to obtain a 2,5-diaminobenzenesulfonic acid (PA-DABSA) composite nanofiltration membrane.

[0060] (7) Immerse the prepared PA-DABSA composite nanofiltration membrane in deionized water for storage.

[0061] When the operating pressure is 0.4 MPa, the rejection rate and flux of sodium sulfate are 96.98% and 7.36 L / m 2 hbar, respectively.

[0062] When the operating pressure is 0.4 MPa, the rejection rate of magnesium chloride is 47.2%; when the operating pressure is 0.4 MPa, the rejection rate of lithium chloride is 79.6%.

[0063] Example 4

[0064] A commercial polymer composite nanofiltration membrane, mostly made of aromatic polyamide nanofiltration membrane material, with a membrane pore size of 0.5–1.2 nm and a membrane area of 20.3 cm 2 , and the aqueous phase concentration of DABSA is 0.7 wt%.

[0065] Preparation method of DABSA sulfonated composite nanofiltration membrane

[0066] (1) Rinse a commercially available aromatic polyamide nanofiltration membrane about 6 cm long with deionized water for pretreatment to remove organic substances, inorganic substances, and microorganisms on its surface, then replace the deionized water and store it until use;

[0067] (2) Disperse 0.7 wt% of DABSA monomer in deionized water, add 0.028 wt% of CTAB phase transfer catalyst to the solution, and adjust the pH of the solution to 10 using NaOH. Prepare a homogeneous aqueous phase solution by ultrasonic method;

[0068] (3) Dissolve 0.1 wt% of 1,3,5-benzenetricarbonyl chloride monomer in n-hexane organic solvent n-hexane, and prepare a homogeneous organic phase solution by ultrasonic method;

[0069] (4) By means of interfacial polymerization, set the temperature of the constant temperature and humidity chamber to 20-40 °C, preferably 35 °C, and the reaction humidity to 20-30% RH, preferably 21% RH. Immerse the aqueous phase solution on the surface of the porous substrate membrane, and after reacting for 5 min, remove the excess aqueous phase solution with a rubber roller;

[0070] (5) After (4) is completed, immerse the organic phase solution on the surface of the porous substrate membrane, pour out the excess organic phase solution after reacting for 1 min, and prepare the primary layer of the sulfonated composite nanofiltration membrane.

[0071] (6) The composite membrane obtained in (5) was placed in a forced-air oven for heat treatment at 60 °C for 10 min, obtaining a 2,5-diaminobenzenesulfonic acid (PA-DABSA) composite nanofiltration membrane.

[0072] (7) The prepared PA-DABSA composite nanofiltration membrane was immersed in deionized water for storage. When the operating pressure was 0.4 MPa, the rejection rate and flux of magnesium chloride were 49.6% and 6.88 L / m 2 h bar, respectively. When the operating pressure was 0.4 MPa, the sodium sulfate rejection rate was 95.77%, and when the operating pressure was 0.4 MPa, the lithium chloride rejection rate was 81.4%.

[0073] Example 5

[0074] Commercially available polymer composite nanofiltration membranes are mostly polysulfone ultrafiltration membrane materials with a membrane pore size of 0.001–0.1 μm and a membrane area of 22.05 cm 2 , and the aqueous phase concentration of DABSA was 0.7 wt%.

[0075] Preparation method of DABSA sulfonated composite nanofiltration membrane

[0076] (1) A polysulfone ultrafiltration membrane about 5 cm long was rinsed and pretreated with deionized water to remove organic substances, inorganic substances, and microorganisms on its surface, and then the deionized water was replaced and stored until use;

[0077] (2) 0.7 wt% of DABSA monomer was dispersed in deionized water, 0.028 wt% of CTAB phase transfer catalyst was added to the solution, and the pH of the solution was adjusted to 10 using NaOH. A homogeneous aqueous phase solution was prepared by ultrasonic method;

[0078] (3) 0.1 wt% of terephthaloyl chloride monomer was dissolved in the organic solvent dichloromethane, and a homogeneous organic phase solution was prepared by ultrasonic method;

[0079] (4) By means of interfacial polymerization, the temperature of the constant temperature and humidity box was set at 20 - 30 °C, preferably 25 °C, and the reaction humidity was 20 - 30% RH, preferably 21% RH. The aqueous phase solution was immersed on the surface of the porous substrate membrane, and after reacting for 5 min, the excess aqueous phase solution was removed with a rubber roller;

[0080] (5) After (4) was completed, the organic phase solution was immersed on the surface of the porous substrate membrane, and after reacting for 1 min, the excess organic phase solution was poured out to prepare the primary layer of the sulfonated composite nanofiltration membrane.

[0081] (6) The composite membrane obtained in (5) was placed in a forced-air oven for heat treatment at 60 °C for 10 min, obtaining a 2,5-diaminobenzenesulfonic acid (PA-DABSA) composite nanofiltration membrane.

[0082] (7) Immerse the prepared PA-DABSA composite nanofiltration membrane in deionized water for storage. When the operating pressure is 0.4 MPa, the rejection rate for lithium chloride is 83.5%, and the rejection rate for magnesium chloride is 42.7%. When the operating pressure is 0.4 MPa, the rejection rate and flux for sodium sulfate are 93.75% and 6.83 L / m 2 h bar, respectively.

[0083] Example 6

[0084] Commercially available polymer composite nanofiltration membranes are mostly poly(piperazine amide) membrane materials with a membrane pore size of 0.5–1.0 nm and a membrane area of 22.05 cm 2 , and the aqueous phase concentration of DABSA is 0.7 wt%.

[0085] Preparation method of PA-DABSA sulfonated composite nanofiltration membrane

[0086] (1) Rinse and pre-treat the poly(piperazine amide) membrane with a length of about 7 cm with deionized water to remove organic substances, inorganic substances, and microorganisms on its surface. Then replace the deionized water and store it until use;

[0087] (2) Disperse 0.7 wt% of DABSA monomer in deionized water, add 0.028 wt% of CTAB phase transfer catalyst to the solution, and adjust the pH of the solution to 10 using NaOH. Prepare a homogeneous aqueous phase solution by ultrasonic method;

[0088] (3) Dissolve 0.1 wt% of cyanuric chloride monomer in cyclopentyl methyl ether organic solvent, and prepare a homogeneous organic phase solution by ultrasonic method;

[0089] (4) By means of interfacial polymerization, set the temperature of the constant temperature and humidity chamber to 20 - 45 °C, preferably 25 °C, and the reaction humidity to 20 - 40% RH, preferably 21% RH. Immerse the aqueous phase solution on the surface of the porous substrate membrane, and after reacting for 5 min, remove the excess aqueous phase solution with a rubber roller;

[0090] (5) After (4) is completed, immerse the organic phase solution on the surface of the porous substrate membrane, pour out the excess organic phase solution after reacting for 1 min, and prepare the primary layer of the sulfonated composite nanofiltration membrane.

[0091] (6) Put the composite membrane obtained in (5) into a blast drying oven for heat treatment at 60 °C for 10 min. Obtain 2,5-diaminobenzenesulfonic acid (PA-DABSA) composite nanofiltration membrane. (7) Immerse the prepared PA-DABSA composite nanofiltration membrane in deionized water for storage. When the operating pressure is 0.4 MPa, the rejection rate for sodium sulfate is 96.9%, and the rejection rate for magnesium chloride is 45.2%.

[0092] Example 7

[0093] A commercial polymer composite nanofiltration membrane, mostly polyurea membrane material, with a membrane pore size of 0.5–2 nm and a membrane area of 7.07 cm 2 , and the aqueous phase concentration of DABSA is 0.7 wt%.

[0094] Preparation method of PA-DABSA sulfonated composite nanofiltration membrane

[0095] (1) A polyurea membrane about 5 cm long is rinsed and pretreated with deionized water to remove organic substances, inorganic substances and microorganisms on its surface, and then the deionized water is replaced and stored until use;

[0096] (2) 0.7 wt% of DABSA monomer is dispersed in deionized water, 0.028 wt% of CTAB phase transfer catalyst is added to the solution, and the pH of the solution is adjusted to 10 with NaOH. An evenly mixed aqueous phase solution is prepared by ultrasonic method;

[0097] (3) 0.1 wt% of toluene diisocyanate monomer is dissolved in toluene organic solvent, and an evenly mixed organic phase solution is prepared by ultrasonic method;

[0098] (4) By means of interfacial polymerization, the temperature of the constant temperature and humidity box is set at 15-30 °C, preferably 25 °C, and the reaction humidity is 20-30% RH, preferably 21% RH. The aqueous phase solution is immersed on the surface of the porous substrate membrane, and after reacting for 5 min, the excess aqueous phase solution is removed with a rubber roller;

[0099] (5) After (4) is completed, the organic phase solution is immersed on the surface of the porous substrate membrane, and after reacting for 1 min, the excess organic phase solution is poured out to prepare the primary layer of the sulfonated composite nanofiltration membrane.

[0100] (6) The composite membrane obtained in (5) is put into a blast drying oven for heat treatment at 60 °C for 10 min. A 2,5-diaminobenzenesulfonic acid (PA-DABSA) composite nanofiltration membrane is obtained. (7) The above-prepared PA-DABSA composite nanofiltration membrane is immersed in deionized water for storage. When the operating pressure is 0.4 MPa, the rejection rate of lithium chloride is 83.5%, and the rejection rate of magnesium chloride is 42.1%.

[0101] Example 8

[0102] A commercial polymer composite nanofiltration membrane, mostly aromatic polyamide nanofiltration membrane material, with a membrane pore size of 0.5–1.2 nm and a membrane area of 25 cm 2 , and the aqueous phase concentration of DABSA is 0.7 wt%.

[0103] Preparation method of PA-DABSA sulfonated composite nanofiltration membrane

[0104] (1) The aromatic polyamide nanofiltration membrane with a length of about 6 cm was rinsed and pretreated with deionized water to remove organic substances, inorganic substances and microorganisms on its surface, and then the deionized water was replaced and stored until use.

[0105] (2) 0.7 wt% of DABSA monomer was dispersed in deionized water, 0.028 wt% of CTAB phase transfer catalyst was added to the solution, and the pH of the solution was adjusted to 10 using NaOH. An evenly mixed aqueous solution was prepared by ultrasonic method.

[0106] (3) 0.1 wt% of cyanuric chloride monomer was dissolved in the organic solvent cyclopentyl methyl ether, and an evenly mixed organic solution was prepared by ultrasonic method.

[0107] (4) By means of interfacial polymerization, the temperature of the constant temperature and humidity box was set at 20 - 40 °C, preferably 35 °C, and the reaction humidity was 20 - 30% RH, preferably 21% RH. The aqueous solution was immersed on the surface of the porous substrate membrane, and after reacting for 5 min, the excess aqueous solution was removed with a rubber roller.

[0108] (5) After (4) was completed, the organic solution was immersed on the surface of the porous substrate membrane, and after reacting for 1 min, the excess organic solution was poured out to prepare the primary layer of the sulfonated composite nanofiltration membrane.

[0109] (6) The composite membrane obtained in (5) was put into a blast drying oven for heat treatment at 60 °C for 10 min to obtain the 2,5-diaminobenzenesulfonic acid (PA-DABSA) composite nanofiltration membrane. (7) The prepared PA-DABSA composite nanofiltration membrane was immersed in deionized water for storage. When the operating pressure was 0.4 MPa, the rejection rate for magnesium chloride was 47.5%, and the rejection rate for lithium chloride was 69.3%.

Claims

1. A method for preparing DABSA sulfonated modified composite nanofiltration membrane in situ by interfacial polymerization, characterized in that: The following steps are involved: (1) Pre-treating the polymer composite base membrane to remove organic matter, inorganic matter and microorganisms on the surface of the base membrane; (2) dispersing the sulfonated amine monomer in deionized water, adding a certain amount of phase transfer catalyst to the solution, adjusting the pH of the solution to alkaline, such as pH 10, and preparing a uniform aqueous phase solution by ultrasonication; (3) dissolving a certain amount of organic phase monomer in an organic solvent to prepare a uniform organic phase solution, which can be further processed by ultrasound; (4) using interfacial polymerization to immerse the aqueous solution into the surface of the porous base membrane, and then using a rubber roller to remove excess aqueous solution after a certain period of time; (5) After (4) is completed, a certain amount of organic phase solution is immersed in the surface of the porous base membrane, and after a certain period of time, the excess organic phase solution is poured out to prepare the primary layer of the sulfonated composite nanofiltration membrane; (6) The composite membrane obtained in (5) is placed in a forced air oven for heat treatment to obtain a 2,5-diaminobenzenesulfonic acid modified composite nanofiltration membrane.

2. The method according to claim 1, characterized in that The substrate can be a commercial polymer composite nanofiltration membrane, the membrane material is aromatic polyamide, polypiperazineamide, sulfonated polysulfone, polyurea, polyether, polydienol / polypiperazineamide mixture, and the pore size of the porous membrane is about 1.0 nm.

3. The method according to claim 1, characterized in that The aqueous phase monomer sulfonated amine monomer used for interfacial polymerization in step (2) is selected from 2,5-diaminobenzenesulfonic acid (DABSA); and its mass percentage concentration in the aqueous phase solution is 0.3-0.9%.

4. The method according to claim 1, characterized in that The mass percentage concentration of the phase transfer catalyst CTAB is 0.012-0.036%.

5. The method according to claim 1, characterized in that Step (3) Organic phase monomers: 1,3,5-trimethylbenzene dicarboxylic acid chloride, terephthaloyl chloride, cyanuric chloride, toluene diisocyanate, isophthaloyl chloride, hexamethylene diisocyanate; mass percentage concentration is 0.08-0.15%, preferably 0.1%; organic solvents: n-hexane, cyclopentyl methyl ether, toluene, dichloromethane, cyclopentane, xylene, chloroform.

6. The method according to claim 1, characterized in that In step (4), the time for the aqueous solution to immerse in the polymer composite membrane is 4-8 minutes, preferably 5 minutes.

7. The method according to claim 1, characterized in that In step (5), the organic phase solution is immersed in the polymer composite membrane for 0.8-1.2 minutes, preferably 1 minute.

8. The method according to claim 1, characterized in that The reaction temperature in steps (4) and (5) is 15-45°C, preferably 25°C, and the reaction humidity is 20-40%RH, preferably 21%RH.

9. The DABSA sulfonated modified composite nanofiltration membrane prepared according to the method described in any one of claims 1 to 8.

10. The use of the DABSA sulfonated modified composite nanofiltration membrane prepared by the method according to any one of claims 1 to 8 as a nanofiltration membrane for the pretreatment process of lithium extraction from a high magnesium lithium salt (magnesium-lithium molar ratio is greater than or equal to 1:1) lake, and the Mg 2+ The purpose of promoting mass transfer is achieved by initially reducing the magnesium-lithium ratio of the salt lake.

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