Separation membrane and method for manufacturing the same, filter cartridge

Abstract

The present application relates to a kind of separation membrane and its preparation method, filter core, the separation membrane includes the nanofiltration separation layer, electrospinning nanofiber layer and modified non-woven fabric stacked in sequence;The nanofiltration separation layer includes the interfacial polymerization product of water-phase raw material and oil-phase raw material;The water-phase raw material includes tannic acid;The electrospinning nanofiber layer includes amine group;The modified non-woven fabric includes amine group;The nanofiltration separation layer, electrospinning nanofiber layer and modified non-woven fabric are combined by the chemical bond formed by tannic acid and amine group;The nanofiltration separation layer and electrospinning nanofiber layer are also combined by the chemical bond formed by amine group and the oil-phase raw material reaction.The separation membrane of the present application can not only remove heavy metals in water, but also reduce the risk of water production scale while retaining minerals;And, the binding ability between each layer of separation membrane is strong, the membrane running stability is high, the membrane thickness is thin, and the water flux is large.

Description

A separation membrane and its preparation method, and a filter element. Technical Field

[0001] This invention relates to a separation membrane, its preparation method, and a filter element. Background Technology

[0002] With the further acceleration of industrialization, the demand for heavy metals from various enterprises is increasing day by day.

[0003] Current technologies primarily utilize reverse osmosis (RO) filters to remove heavy metals from water. The working principle of an RO filter is to apply pressure to the water, forcing water molecules and ionic minerals through the membrane. Most inorganic salts, including heavy metals, organic matter, bacteria, and viruses cannot pass through the membrane. RO filters effectively remove heavy metals and improve drinking water quality, but they also remove some minerals. Health experts and practical experience have shown that pure water without minerals is not suitable for long-term consumption, especially for the elderly, pregnant women, and children, as it is detrimental to their health. This is because the human body needs minerals for metabolism, and drinking water is one of the main sources of minerals and trace elements. Nanofiltration is a water treatment technology whose main characteristic is that it can appropriately retain beneficial minerals. Its ability to retain ions of different valence states varies considerably, but it also retains some heavy metals.

[0004] Currently, water purifiers on the market use a combination of nanofiltration and NSP (membrane chromatography) filters to achieve the effect of removing heavy metals while retaining minerals. Firstly, this multi-filter combination results in larger filter volumes, more complex water circuits, higher water resistance, and lower flow rates. Secondly, the need for multiple filters and structural components in the composite filter setup increases overall costs. Finally, this multi-filter combination is prone to scale buildup. Tap water typically contains a certain concentration of calcium and magnesium ions; when the water is heated or evaporates, these compounds precipitate, forming scale inside the purifier. When the scale buildup reaches a certain thickness, it reduces water flow, affecting the normal operation of the water purifier. Summary of the Invention

[0005] The technical problem to be solved is to overcome the shortcomings of existing separation membranes or filter cartridges, such as insufficient water flux, inability to retain minerals while removing heavy metals and reducing the risk of scaling in produced water, and poor performance stability. Therefore, a separation membrane, its preparation method, and filter cartridge are provided. The separation membrane and filter cartridge can not only remove heavy metals from water, but also retain minerals while reducing the risk of scaling in produced water. Furthermore, the separation membrane has strong bonding between its layers, high membrane operation stability, thin membrane thickness, and large water flux.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution:

[0007] This invention provides a separation membrane comprising a nanofiltration separation layer, an electrospun nanofiber layer, and a modified nonwoven fabric stacked sequentially.

[0008] The nanofiltration separation layer contains interfacial polymerization products of aqueous and oil phase feedstocks;

[0009] The aqueous phase raw material contains tannic acid;

[0010] The electrospun nanofiber layer contains amine groups;

[0011] The modified nonwoven fabric contains amine groups;

[0012] The nanofiltration separation layer, the electrospun nanofiber layer, and the modified nonwoven fabric are bonded together by chemical bonds formed by tannic acid and amine groups.

[0013] The nanofiltration separation layer and the electrospun nanofiber layer are also bonded together by chemical bonds formed by the reaction of amine groups with the oil phase raw material.

[0014] Preferably, the separation membrane satisfies one or more of the following conditions:

[0015] ① The thickness of the separation membrane is 90-100 μm, for example, 93 μm, 95 μm and 96 μm;

[0016] ② The thickness of the nanofiltration separation layer is 30-100 nm;

[0017] Preferably, the thickness of the nanofiltration separation layer is 45-90 nm, for example, 49 nm, 63 nm and 85 nm;

[0018] ③ The thickness of the electrospun nanofiber layer is 5-20 μm, for example, 5 μm, 10 μm and 20 μm;

[0019] ④ The thickness of the modified nonwoven fabric is 60-90μm, for example, 73μm, 86μm and 90μm.

[0020] The present invention also provides a method for preparing a separation membrane, which includes the following steps:

[0021] S1, Modified nonwoven fabric is obtained by using polyamine compounds;

[0022] S2, using electrospinning process to spin a spinning solution formed by polyamine compounds, crosslinking agents and polyurethane into filaments, using modified nonwoven fabric as receiving substrate to form a nanofiber membrane, which serves as the base membrane.

[0023] S3, the base film is sequentially immersed in an aqueous solution containing aqueous raw materials and an oil solution containing oil raw materials, and then dried;

[0024] The aqueous raw material contains tannic acid.

[0025] In this scheme, modified nonwoven fabric and nanofiber membrane are used as base membranes. The electrospinning process for preparing nanofiber membranes is simpler and lower in cost than the phase conversion process for preparing ultrafiltration membranes, and uses less organic solvent, which has the advantage of being green and environmentally friendly. Furthermore, since the modified nonwoven fabric has amine groups on its surface, it can further enhance the removal capacity of heavy metals, and the modified nonwoven fabric has a stronger continuous ability to remove heavy metals.

[0026] In this invention, preferably, step S1 satisfies one or more of the following conditions:

[0027] ①The modification method involves immersing the nonwoven fabric in an aqueous solution of a polyamine compound for reaction;

[0028] The reaction temperature is preferably 70-90°C, for example, 70°C, 80°C and 90°C;

[0029] The optimal reaction time is 12 hours;

[0030] ②The nonwoven fabric is a polyester nonwoven fabric;

[0031] ③ In the aqueous solution of the polyamine compound, the mass fraction of the polyamine compound is 1-10%, for example, 1%, 5% and 10%, based on the mass fraction of the polyamine compound relative to the total mass of the aqueous solution.

[0032] In this invention, preferably, step S2 satisfies one or more of the following conditions:

[0033] ①The mass fraction of the polyamine compound is 5-10%, for example, 5%, 7% and 10%, based on the mass fraction of each component relative to the total mass of the spinning solution;

[0034] ② The mass fraction of the crosslinking agent is 1-2%, for example, 1%, 1.5% and 2%;

[0035] ③The crosslinking agent includes at least one of epichlorohydrin, glutaraldehyde, and glycidyl methacrylate;

[0036] ④ The film-forming material includes at least one of polyurethane, polysulfone, polyethersulfone, and polyamide;

[0037] The film-forming material is preferably polyurethane;

[0038] ⑤ The mass fraction of the film-forming material is 15-20%, for example, 15%, 17% and 20%;

[0039] ⑥ The polyamine compounds include one or a combination of at least two of tetraethylenepentamine, polyethyleneimine, and chitosan;

[0040] The molecular weight of the polyamine compound is preferably above 100 kDa;

[0041] The polyamine compound preferably contains multiple amine groups, such as primary amine groups;

[0042] ⑦ The raw materials for the spinning solution also include lithium chloride;

[0043] Preferably, the lithium chloride has a mass fraction of 1-3%, for example, 1%, 2%, and 3%.

[0044] In this scheme, the amine groups on the electrospun nanofiber layer and the modified nonwoven fabric are used to: 1) form complexes with heavy metal ions to achieve the adsorption and removal of heavy metals; 2) the amine groups react with tannic acid to form a Schiff base reaction, which improves the bonding force between the membranes; 3) the amine groups on the electrospun nanofiber layer react with the oil phase raw materials, which increases the positive charge in the nanofiltration separation layer, improves the removal capacity of calcium and magnesium ions, and reduces the risk of scaling in the produced water.

[0045] In this invention, in step S2, preferably, the process of forming the spinning solution is as follows: the raw materials and solvent are mixed evenly, heated and stirred to obtain the spinning solution;

[0046] The time for achieving uniform mixing is preferably 0.5-1 hour, for example, 0.5 hours;

[0047] The preferred temperature for heating and stirring is 80°C;

[0048] The heating and stirring time is preferably 1-2 hours, for example, 1 hour, 1.5 hours and 2 hours;

[0049] The viscosity of the spinning solution is 700-1500 mPa·s.

[0050] In step S2, preferably, the electrospinning process satisfies one or more of the following conditions:

[0051] The electrospinning voltage of the electrospinning process is 70-95kV, for example, 70kV, 80kV and 90kV;

[0052] The distance between the electrode wire and the collector in the electrospinning process is 15-25cm, for example, 15cm, 20cm and 25cm;

[0053] The liquid supply rate of the electrospinning process is 5-200 mL / h, for example, 20 mL / h, 100 mL / h and 200 mL / h;

[0054] The collector speed in the electrospinning process is 0.01-0.05 m / min, for example, 0.015 m / min, 0.03 m / min and 0.05 m / min;

[0055] The temperature of the electrospinning process is 20-40℃, for example, 20℃, 30℃ and 40℃;

[0056] The humidity of the electrospinning process is 20-40%, for example, 20%, 30%, and 40%.

[0057] In step S2, preferably, the nanofiber membrane satisfies one or more of the following conditions:

[0058] The specific surface area of ​​the nanofiber membrane is 500-950 m². 2 / g;

[0059] The porosity of the nanofiber membrane is 60-80%;

[0060] The nanofiber membrane has a fiber diameter of 70-300 nm.

[0061] In this scheme, the high porosity of the nanofiber membrane and nonwoven fabric can fully absorb the aqueous solution. Therefore, the aqueous concentration in this scheme is 10 times lower than that in traditional nanofiltration preparation, which reduces environmental pollution and lowers costs. Furthermore, the low aqueous concentration can effectively reduce the thickness of the nanofiltration separation layer and increase the flux of the separation membrane.

[0062] In this invention, preferably, in step S3, the soaking treatment satisfies one or more of the following conditions:

[0063] The base membrane is immersed in the aqueous solution for 5-10 minutes, for example, 5 minutes, 7 minutes and 10 minutes;

[0064] After the base membrane is immersed in an aqueous solution, excess aqueous solution is removed from the surface of the base membrane.

[0065] The base film is immersed in the oil phase solution for 1-3 minutes, for example, 1 minute, 2 minutes and 3 minutes;

[0066] After the base film is immersed in the oil phase solution, excess oil phase solution is removed from the surface of the base film.

[0067] The aqueous and oil phase solutions can be prepared at room temperature.

[0068] In step S3, preferably, the drying step involves placing the base membrane, which has been soaked in the oil phase solution, into an oven for reaction to obtain a separation membrane;

[0069] The temperature of the oven is 60-80°C, for example, 60°C, 70°C and 80°C;

[0070] The reaction time is 5-10 minutes, for example, 5 minutes, 7 minutes, and 10 minutes.

[0071] In step S3, preferably, the aqueous solution is an aqueous solution of piperazine and tannic acid, wherein the mass fraction of piperazine is 0.01-0.05%, for example, 0.01%, 0.03%, and 0.05%.

[0072] The mass fraction of the tannic acid is 0.01-0.05%, for example, 0.01%, 0.03%, and 0.05%;

[0073] The pH value of the aqueous solution is 10-11;

[0074] The oil phase solution is a hexane solution of trimesoyl chloride, wherein the mass fraction of trimesoyl chloride is 0.01-0.04%, for example, 0.01%, 0.02%, and 0.04%.

[0075] In this scheme, tannic acid is added to the aqueous solution: 1) As an aqueous raw material, tannic acid can utilize the hydrogen bonding interaction between tannic acid and piperazine to further reduce the diffusion rate of piperazine in the aqueous phase, thereby reducing the reaction rate between piperazine and the oil phase raw material, thus reducing the thickness of the nanofiltration separation layer and increasing the membrane flux; 2) The reactivity of tannic acid with amine groups increases the bonding force between the modified nonwoven fabric and the nanofiber membrane; 3) The reactivity of tannic acid with amine groups strengthens the bonding force between the electrospun nanofiber layer and the nanofiltration separation layer; 4) Some tannic acid is doped into the nanofiltration separation layer in monomer form, which makes the nanofiltration separation layer relatively loose but does not affect the separation pore size of the separation layer. Therefore, while increasing the nanofiltration membrane flux, the heavy metal removal effect can be guaranteed. On the other hand, since tannic acid exists in molecular form and forms a complex with heavy metal ions, the heavy metal removal effect can be improved.

[0076] In this scheme, the reaction between the oil phase raw material and the amine groups in the electrospun nanofiber layer is utilized to enhance the separation membrane's resistance to positively charged divalent ions (Ca). 2+ Mg 2+ Its removal capacity effectively reduces the risk of scale buildup in the filter cartridge's water.

[0077] The present invention further provides a separation membrane, which is prepared by the above-described separation membrane preparation method.

[0078] The present invention also provides a filter element comprising the separation membrane and auxiliary materials as described above.

[0079] The auxiliary materials include a flow guide cloth, a partition net, and a central tube.

[0080] According to a preferred embodiment of the present invention, the separation membrane of this preferred embodiment exhibits retention rates of 35%, 29%, 27%, and 26% for minerals such as potassium ions, sodium ions, lithium ions, and bicarbonate, respectively, and removal rates of heavy metals such as lead, cadmium, chromium, and arsenic reaching 99.1%, 99.9%, 97.4% or more, and 99.5%, respectively. Furthermore, it also removes Ca... 2+ Mg 2+ The retention rates were 8% and 11%, respectively. This separation membrane not only removes heavy metals from water but also retains minerals while reducing the risk of scaling in the produced water. The specific technical solution is as follows:

[0081] Modified nonwoven fabric is obtained by modifying nonwoven fabric with polyamine compounds; a spinning solution consisting of chitosan, glycidyl methacrylate, polyurethane, and lithium chloride is spun into fibers using an electrospinning process, and a polyethylene diaphragm is used as the receiving substrate to form a nanofiber membrane, which serves as the base membrane; the base membrane is then sequentially immersed in an aqueous solution containing tannic acid and a hexane solution containing trimesoyl chloride, and finally dried.

[0082] The chitosan, glycidyl methacrylate, polyurethane, and lithium chloride are present in mass fractions of 10%, 2%, 20%, and 3%, respectively. The spinning solution is formed by stirring the raw materials and solvent for 0.5 hours to mix them evenly, heating the solution to 80°C, and stirring for another 2 hours to obtain the final spinning solution. The electrospinning process uses a spinning voltage of 90 kV, a distance of 25 cm between the electrode thread and the collector, a liquid supply rate of 200 mL / h, a collector speed of 0.05 m / min, a spinning temperature of 40°C, and a humidity of 40%.

[0083] Further, the base membrane is immersed in the aqueous solution for 10 minutes; the base membrane is immersed in the oil solution for 3 minutes; the drying step involves placing the base membrane, after being immersed in the oil solution, into an oven to react and obtain a separation membrane, the oven temperature being 80°C; the reaction time being 10 minutes; the aqueous solution consists of 0.05% piperazine and 0.05% tannic acid; the oil solution is a 0.04% hexane solution of trimesoyl chloride.

[0084] The positive and progressive effects of this invention are as follows:

[0085] ① Achieving the effect of retaining minerals and removing heavy metals: The separation membrane retains some minerals, while the amine groups on the electrospun nanofiber layer and the modified nonwoven fabric, as well as the tannic acid in the nanofiltration separation layer, achieve efficient adsorption and removal of heavy metals. The combined function of these two components gives the separation membrane the characteristic of selective separation of heavy metals and minerals.

[0086] ② Improve the bonding force between the layers of the separation membrane and enhance membrane operation stability: By utilizing the reactivity of tannic acid with amine groups and the reactivity of tannic acid with trimesoyl chloride, the bonding force between the layers of the separation membrane is strengthened, thereby effectively reducing the decline in membrane performance caused by long-term operation and improving membrane operation stability.

[0087] ③ Improve the separation membrane's ability to handle Ca 2+ Mg 2+ The removal capacity of the membrane in this invention reduces the risk of scaling in the produced water: the membrane removes positively charged divalent ions (Ca ions) and reduces the risk of scaling in the produced water. 2+ Mg 2+ It has a strong removal capacity and can effectively reduce the risk of scale buildup in the filter cartridge's water. Detailed Implementation

[0088] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.

[0089] Example 1

[0090] I. Preparation of Modified Nonwoven Fabrics

[0091] 1. Preparation of modified solution: Dissolve 1g of polyethyleneimine in 99g of water and stir to obtain a homogeneous solution;

[0092] 2. Modification process: Immerse a 90μm thick nonwoven fabric in the modification solution, heat it to 70℃, remove it after 12 hours, and wash it with pure water to obtain the modified nonwoven fabric.

[0093] II. Preparation of Separation Membranes

[0094] 1. Dissolve 5g tetraethylenepentamine, 1g epichlorohydrin, 15g polyurethane, and 1g lithium chloride in 78g N,N-dimethylacetamide and stir for 0.5h to obtain a homogeneous solution.

[0095] 2. Heat the solution to 80°C and stir for 1 hour to obtain the final spinning solution;

[0096] 3. The spinning solution is used to form a nanofiber layer on the surface of the nonwoven fabric through an electrospinning device: the spinning voltage is 70kV, the distance between the electrode wire and the collector is 15cm, the liquid supply rate is 20mL / h, the collector speed is 0.015m / min, the spinning temperature is 20℃, and the humidity is 20%.

[0097] 4. Immerse the base film obtained in step 3 in the aqueous solution, remove it after 5 minutes, and remove excess solution from the surface. The aqueous solution consists of 0.01% piperazine and 0.01% tannic acid.

[0098] 5. Immerse the base film from step 4 in the oil phase solution for 1 minute, then remove it and remove excess oil phase solution from the surface. The oil phase solution is a 0.01% hexane solution of trimesoyl chloride.

[0099] 6. Place the base membrane from step 5 into a 60°C oven and react for 5 minutes to obtain a novel separation membrane capable of removing heavy metals while retaining minerals.

[0100] 7. The separation membrane from step 6 is wound together with auxiliary materials such as the flow guide cloth, the separator, and the central tube to form a filter element, thereby obtaining a filter element that can efficiently remove heavy metals and effectively retain minerals.

[0101] Example 2

[0102] I. Preparation of Modified Nonwoven Fabrics

[0103] 1. Preparation of modified solution: Dissolve 5g of polyethyleneimine in 95g of water and stir to obtain a homogeneous solution;

[0104] 2. Modification process: Immerse a nonwoven fabric with a thickness of 86μm in the modification solution, heat it to 80℃, take it out after 12 hours, and wash it with pure water to obtain the modified nonwoven fabric.

[0105] II. Preparation of Separation Membranes

[0106] 1. Dissolve 7g polyethyleneimine, 1.5g glutaraldehyde, 17g polyurethane, and 2g lithium chloride in 72.5g N,N-dimethylacetamide and stir for 1 hour to obtain a homogeneous solution.

[0107] 2. Heat the solution to 80℃ and stir for 1.5 hours to obtain the final spinning solution;

[0108] 3. The spinning solution is used to form a nanofiber layer on the surface of the nonwoven fabric through an electrospinning device: the spinning voltage is 80kV, the distance between the electrode wire and the collector is 20cm, the liquid supply rate is 100mL / h, the collector speed is 0.03m / min, the spinning temperature is 30℃, and the humidity is 30%.

[0109] 4. Immerse the base film obtained in step 3 in the aqueous solution, remove it after 7 minutes, and remove excess solution from the surface. The aqueous solution consists of 0.03% piperazine and 0.03% tannic acid.

[0110] 5. Immerse the base film from step 4 in the oil phase solution for 2 minutes, then remove it and remove excess oil phase solution from the surface. The oil phase solution is a 0.02% hexane solution of trimesoyl chloride.

[0111] 6. Place the base membrane from step 5 into a 70°C oven and react for 7 minutes to obtain a novel separation membrane capable of removing heavy metals while retaining minerals.

[0112] 7. The separation membrane from step 6 is wound together with auxiliary materials such as the flow guide cloth, the separator, and the central tube to form a filter element, thereby obtaining a filter element that can efficiently remove heavy metals and effectively retain minerals.

[0113] Example 3

[0114] I. Preparation of Modified Nonwoven Fabrics

[0115] 1. Preparation of modified solution: Dissolve 10g of polyethyleneimine in 90g of water and stir to obtain a homogeneous solution;

[0116] 2. Modification process: Immerse a 73μm thick nonwoven fabric in the modification solution, heat it to 90℃, remove it after 12 hours, and wash it with pure water to obtain the modified nonwoven fabric.

[0117] II. Preparation of Separation Membranes

[0118] 1. Dissolve 10g chitosan, 2g glycidyl methacrylate, 20g polyurethane, and 3g lithium chloride in 65g N,N-dimethylacetamide and stir for 1 hour to obtain a homogeneous solution.

[0119] 2. Heat the solution to 80°C and stir for 2 hours to obtain the final spinning solution;

[0120] 3. The spinning solution is used to form a nanofiber layer on the surface of the nonwoven fabric through an electrospinning device: the spinning voltage is 90kV, the distance between the electrode wire and the collector is 25cm, the liquid supply rate is 200mL / h, the collector speed is 0.05m / min, the spinning temperature is 40℃, and the humidity is 40%.

[0121] 4. Immerse the base film obtained in step 3 in the aqueous solution, remove it after 10 minutes, and remove excess solution from the surface. The aqueous solution consists of 0.05% piperazine and 0.05% tannic acid.

[0122] 5. Immerse the base film from step 4 in the oil phase solution for 3 minutes, then remove it and remove excess oil phase solution from the surface. The oil phase solution is a 0.04% hexane solution of trimesoyl chloride.

[0123] 6. Place the base membrane from step 5 into an 80°C oven and react for 10 minutes to obtain a novel separation membrane capable of removing heavy metals while retaining minerals.

[0124] 7. The separation membrane from step 6 is wound together with auxiliary materials such as the flow guide cloth, the separator, and the central tube to form a filter element, thereby obtaining a filter element that can efficiently remove heavy metals and effectively retain minerals.

[0125] Comparative Example 1

[0126] 1. Immerse the ultrafiltration substrate in the aqueous solution for 5 minutes, then remove it and remove excess solution from the surface. The aqueous solution consists of 0.4% piperazine.

[0127] 2. Immerse the base film from step 1 in the oil phase solution for 1 minute, then remove it and remove excess oil phase solution from the surface. The oil phase solution is a 0.2% hexane solution of trimesoyl chloride.

[0128] 3. Place the base membrane from step 2 into a 60°C oven and react for 10 minutes to obtain a nanofiltration membrane.

[0129] 4. The separation membrane from step 3 is wound together with auxiliary materials such as flow guide cloth, separator, and central tube to form a filter element, thus obtaining a nanofiltration filter element.

[0130] Example 1

[0131] Comparison of heavy metal removal rate, mineral retention rate, membrane thickness, and water flux in Examples 1-3 and Comparative Example 1:

[0132] I. Heavy metal removal rate:

[0133] 1) Preparation of heavy metal solution: Prepare heavy metal solution according to GB30307 requirements;

[0134] 2) Heavy metal removal effect test: Pass the prepared heavy metal solution into the filter element, and after stabilization, take 10 mL of the filtrate; at the same time, take 10 mL of the original solution.

[0135] 3) Heavy metal concentration test: The heavy metal concentrations of the filtrate and the original solution were tested using an atomic absorption spectrometer and recorded as C1 and C2;

[0136] 4) Calculate the heavy metal removal rate:

[0137]

[0138] II. Mineral Retention Rate:

[0139] 1) Prepare mineral solution: Prepare mineral solution according to CB30307 requirements;

[0140] 2) Mineral removal effect test: Pass the prepared mineral solution into the filter element, and after stabilization, take 50 mL of the filtrate; at the same time, take 50 mL of the original solution.

[0141] 3) Mineral solution concentration test: The mineral concentration of the filtrate and the original solution was tested using a conductivity meter and recorded as C3 and C4;

[0142] 4) Calculate the heavy metal removal rate:

[0143]

[0144] III. Film thickness test:

[0145] 1) Thickness test: The thickness of the prepared separation membrane was tested using a thickness gauge.

[0146] IV. Flux Test (Separation Membrane):

[0147] 1) Membrane cutting: Cut the membrane into circular pieces with a diameter of 55mm according to the size of the filter tank;

[0148] 2) Flux test: Place the circular membrane in the filter tank, fix it, and then pass pure water through it. Test at 6 bar. After stabilization, use a beaker to collect a certain amount of water (volume recorded as V1, unit is L) and record the time of water collection (recorded as t1, unit is h).

[0149] 3) Flux calculation (denoted as L, unit is L / (m)) 2 *h*bar)):

[0150]

[0151] The specific test results are as follows:

[0152] Table 1 Comparison of Heavy Metal Removal Rates

[0153]

[0154]

[0155] As shown in Table 1, the heavy metal adsorption capacity of the filter element prepared by the method in Comparative Example 1 is far inferior to that of Examples 1-3 of this application. The reason is that Comparative Example 1 does not contain polyamine compounds or tannic acid.

[0156] Table 2 Comparison of mineral retention rates

[0157] Mineral Retention Rate* Example 1 Example 2 Example 3 Comparative Example 1 Potassium 43% 38% 35% 29% Calcium 23% 13% 8% 35% Sodium 39% 36% 29% 23% Magnesium 22% 15% 11% 40% Lithium 35% 33% 27% 19% Bicarbonate 35% 29% 26% 20% surface

[0158] *Note: Potassium chloride solution was used to determine the retention rate of potassium ions; calcium chloride solution was used to determine the retention rate of calcium ions; sodium chloride solution was used to determine the retention rate of sodium ions; magnesium chloride solution was used to determine the retention rate of magnesium ions; lithium chloride solution was used to determine the retention rate of lithium ions; and sodium bicarbonate solution was used to determine the retention rate of bicarbonate. All of the above were measured separately in a single run.

[0159] As shown in Table 2, for all but Ca 2+ Mg 2+ In addition to the minerals mentioned above, the mineral retention capacity of the filter element prepared in Comparative Example 1 is weaker than that of Examples 1-3 of this application. This indicates that the separation membrane prepared by the method of this application has a better mineral retention effect.

[0160] Furthermore, as shown in Table 2, for Ca 2+ Mg 2+ The filter element prepared in Comparative Example 1 has a positive effect on Ca. 2+ and Mg 2+ The retention rates reached 35% and 40% respectively, which are higher than those of Examples 1-3 of this application. 2+ Mg 2+ The lower the retention rate, the less likely scaling will occur. In Examples 1-3 of this application, while the overall mineral retention rate is higher than that of Comparative Example 1, the Ca content is also guaranteed. 2+ Mg 2+ The low retention rate not only preserves beneficial minerals in the water but also reduces the risk of scale buildup in the filter cartridge. In particular, the filter cartridge of Example 3 of this application exhibits excellent retention of Ca... 2+ The retention rate was only 8%, for Mg 2+ The retention rate was only 11%, which is quite good.

[0161] Comparative Example 1 cannot guarantee Ca 2+ Mg 2+ The low retention rate is due to the absence of polyamine compounds in its separation membrane, making it impossible to utilize polyamine compounds to react with oil phase monomers, thereby increasing the positive charge of the nanofiltration separation layer and enhancing the composite separation membrane's ability to handle positively charged divalent ions (Ca). 2+ Mg 2+ ) removal ability.

[0162] Table 3 Comparison of membrane structure and properties

[0163]

[0164] Note: “——” in the table indicates that the separation membrane does not contain this structure, and therefore the thickness cannot be measured.

[0165] The separation membranes prepared in Examples 1-3 of the present invention comprise a nanofiltration separation layer, an electrospun nanofiber layer, and a modified nonwoven fabric stacked sequentially; the nanofiltration separation layer contains an interfacial polymerization product of tannic acid and trimesoyl chloride; the electrospun nanofiber layer and the modified nonwoven fabric contain amine groups; the nanofiltration separation layer, the electrospun nanofiber layer, and the modified nonwoven fabric are bonded by chemical bonds formed by tannic acid and amine groups; the nanofiltration separation layer and the electrospun nanofiber layer are also bonded by chemical bonds formed by the reaction of amine groups and trimesoyl chloride.

[0166] As shown in Table 3, the thickness of the separation membrane and the nanofiltration separation layer of Comparative Example 1 are much thicker than those of Examples 1-3, and the water flux of the separation membrane of Comparative Example 1 is also much lower than that of Examples 1-3.

[0167] It is known that the filter element prepared by the present invention can achieve the technical effect of removing heavy metals while retaining minerals, and can achieve a large water flow rate.

[0168] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A separation membrane, characterized in that, The device comprises a nanofiltration separation layer, an electrospun nanofiber layer, and a modified nonwoven fabric stacked sequentially. The nanofiltration separation layer contains an interfacial polymerization product of an aqueous phase raw material and an oil phase raw material. The aqueous phase raw material contains tannic acid. The electrospun nanofiber layer contains amine groups. The modified nonwoven fabric contains amine groups. The nanofiltration separation layer, the electrospun nanofiber layer, and the modified nonwoven fabric are bonded by chemical bonds formed by tannic acid and amine groups. The nanofiltration separation layer and the electrospun nanofiber layer are also bonded by chemical bonds formed by the reaction of amine groups with the oil phase raw material. The amine groups are derived from polyamine compounds, including one or a combination of at least two of tetraethylenepentamine, polyethyleneimine, and chitosan.

2. The separation membrane according to claim 1, characterized in that, The separation membrane satisfies one or more of the following conditions: the thickness of the separation membrane is 90-100 μm; the thickness of the nanofiltration separation layer is 30-100 nm; the thickness of the electrospun nanofiber layer is 5-20 μm; and the thickness of the modified nonwoven fabric is 60-90 μm.

3. The separation membrane according to claim 2, characterized in that, The thickness of the separation membrane is 93 μm, 95 μm, or 96 μm.

4. The separation membrane according to claim 2, characterized in that, The thickness of the nanofiltration separation layer is 45-90 nm.

5. The separation membrane according to claim 2, characterized in that, The thickness of the nanofiltration separation layer is 49 nm, 63 nm, or 85 nm.

6. The separation membrane according to claim 2, characterized in that, The thickness of the electrospun nanofiber layer is 5 μm, 10 μm, or 20 μm.

7. The separation membrane according to claim 2, characterized in that, The thickness of the modified nonwoven fabric is 73μm, 86μm or 90μm.

8. A method for preparing a separation membrane, characterized in that, The process includes the following steps: S1, modifying nonwoven fabric with polyamine compounds to obtain modified nonwoven fabric; S2, spinning a spinning solution formed by polyamine compounds, crosslinking agents, and film-forming materials into filaments using an electrospinning process, using the modified nonwoven fabric as the receiving substrate to form a nanofiber membrane, which serves as the base membrane; S3, sequentially immersing the base membrane in an aqueous solution containing aqueous raw materials and an oil solution containing oil raw materials, and then drying it; the aqueous raw materials include tannic acid; the polyamine compounds include one or a combination of at least two of tetraethylenepentamine, polyethyleneimine, and chitosan.

9. The preparation method according to claim 8, characterized in that, In step S1, the modification method is to soak the nonwoven fabric in an aqueous solution of polyamine compounds for reaction; and / or, the nonwoven fabric is a polyester nonwoven fabric; and / or, the mass fraction of the polyamine compounds in the aqueous solution is 1%-10%, based on the mass fraction of the polyamine compounds in the total mass of the aqueous solution.

10. The preparation method according to claim 9, characterized in that, The reaction temperature is 70-90℃.

11. The preparation method according to claim 9, characterized in that, The reaction temperature is 70°C, 80°C, or 90°C.

12. The preparation method according to claim 9, characterized in that, The reaction time was 12 hours.

13. The preparation method according to claim 9, characterized in that, The mass fraction of the polyamine compound is 1%, 5%, or 10%.

14. The preparation method according to claim 8, characterized in that, In step S2, based on the mass fraction of each component relative to the total mass of the spinning solution, the mass fraction of the polyamine compound is 5%-10%; and / or, the mass fraction of the crosslinking agent is 1%-2%; and / or, the crosslinking agent includes at least one of epichlorohydrin, glutaraldehyde, and glycidyl methacrylate; and / or, the film-forming material includes at least one of polyurethane, polysulfone, polyethersulfone, and polyamide; and / or, the mass fraction of the film-forming material is 15%-20%; and / or, the raw materials of the spinning solution also include lithium chloride; and / or, the spinning solution is formed by mixing each raw material with a solvent evenly, heating and stirring to obtain the spinning solution; and / or, the viscosity of the spinning solution is 700-1500 mPa·s.

15. The preparation method according to claim 14, characterized in that, The mass fraction of the polyamine compound is 5%, 7%, or 10%.

16. The preparation method according to claim 14, characterized in that, The mass fraction of the crosslinking agent is 1%, 1.5%, or 2%.

17. The preparation method according to claim 14, characterized in that, The film-forming material is polyurethane.

18. The preparation method according to claim 14, characterized in that, The mass fraction of the film-forming material is 15%, 17%, or 20%.

19. The preparation method according to claim 14, characterized in that, The polyamine compound has a molecular weight of 100 kDa or higher.

20. The preparation method according to claim 14, characterized in that, The polyamine compounds contain multiple amine groups.

21. The preparation method according to claim 14, characterized in that, The polyamine compounds contain multiple primary amine groups.

22. The preparation method according to claim 14, characterized in that, The mass fraction of the lithium chloride is 1%-3%.

23. The preparation method according to claim 14, characterized in that, The mass fraction of the lithium chloride is 1%, 2%, or 3%.

24. The preparation method according to claim 14, characterized in that, The time for uniform mixing is 0.5-1 hour.

25. The preparation method according to claim 14, characterized in that, The time for uniform mixing is 0.5 hours.

26. The preparation method according to claim 14, characterized in that, The heating and stirring temperature is 80°C.

27. The preparation method according to claim 14, characterized in that, The heating and stirring time is 1-2 hours.

28. The preparation method according to claim 14, characterized in that, The heating and stirring time is 1 hour, 1.5 hours, or 2 hours.

29. The preparation method according to claim 8, characterized in that, In step S2, the electrospinning process satisfies one or more of the following conditions: the spinning voltage of the electrospinning process is 70-95kV; the distance between the electrode wire and the collector in the electrospinning process is 15-25cm; the liquid supply rate of the electrospinning process is 5-200mL / h; the speed of the collector in the electrospinning process is 0.01-0.05m / min; the temperature of the electrospinning process is 20-40℃; the humidity of the electrospinning process is 20-40%; and / or, the nanofiber membrane satisfies one or more of the following conditions: the specific surface area of ​​the nanofiber membrane is 500-950m². 2 / g; the porosity of the nanofiber membrane is 60%-80%; the fiber diameter of the nanofiber membrane is 70-300nm.

30. The preparation method according to claim 29, characterized in that, In step S2, the electrospinning process satisfies one or more of the following conditions: the spinning voltage of the electrospinning process is 70kV, 80kV, or 90kV; the distance between the electrode wire and the collector in the electrospinning process is 15cm, 20cm, or 25cm; the liquid supply rate of the electrospinning process is 20mL / h, 100mL / h, or 200mL / h; the speed of the collector in the electrospinning process is 0.015m / min, 0.03m / min, or 0.05m / min; the temperature of the electrospinning process is 20℃, 30℃, or 40℃; and the humidity of the electrospinning process is 20%, 30%, or 40%.

31. The preparation method according to claim 8, characterized in that, In step S3, the immersion treatment satisfies one or more of the following conditions: the immersion time of the base membrane in the aqueous solution is 5-10 min; after the immersion treatment of the base membrane in the aqueous solution, excess aqueous solution on the surface of the base membrane is removed; the immersion time of the base membrane in the oil solution is 1-3 min; after the immersion treatment of the base membrane in the oil solution, excess oil solution on the surface of the base membrane is removed. And / or, the drying step involves placing the base membrane, which has been soaked in an oil phase solution, into an oven for reaction to obtain a separation membrane.

32. The preparation method according to claim 31, characterized in that, The base membrane is immersed in the aqueous solution for 5 min, 7 min, or 10 min.

33. The preparation method according to claim 31, characterized in that, The base film is immersed in the oil phase solution for 1 min, 2 min, or 3 min.

34. The preparation method according to claim 31, characterized in that, The temperature of the oven is 60-80℃.

35. The preparation method according to claim 31, characterized in that, The temperature of the oven is 60°C, 70°C, or 80°C.

36. The preparation method according to claim 31, characterized in that, The reaction time is 5-10 minutes.

37. The preparation method according to claim 31, characterized in that, The reaction time is 5 min, 7 min, or 10 min.

38. The preparation method according to claim 8, characterized in that, In step S3, the aqueous phase solution is an aqueous solution of piperazine and tannic acid, wherein the mass fraction of piperazine is 0.01%-0.05%; the mass fraction of tannic acid is 0.01%-0.05%; and / or, the pH value of the aqueous phase solution is 10-11; and / or, the oil phase solution is a hexane solution of trimesoyl chloride, wherein the mass fraction of trimesoyl chloride is 0.01%-0.04%.

39. The preparation method according to claim 38, characterized in that, The piperazine has a mass fraction of 0.01%, 0.03%, or 0.05%.

40. The preparation method according to claim 38, characterized in that, The mass fraction of the tannic acid is 0.01%, 0.03%, or 0.05%.

41. The preparation method according to claim 38, characterized in that, The mass fraction of the pyromellitic chloroformyl chloride is 0.01%, 0.02%, or 0.04%.

42. A separation membrane, characterized in that, The separation membrane is prepared by the preparation method according to any one of claims 8-41.

43. A filter element, characterized in that, It includes a separation membrane and auxiliary materials as described in any one of claims 1-7 and 42; wherein the auxiliary materials include a flow guide cloth, a separator, and a central tube.

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