Separation membrane and method for manufacturing the same, filter cartridge

Abstract

The application discloses a separation membrane and a preparation method and a filter element thereof, and the separation membrane comprises a nanofiltration separation layer, an electrospinning nanofiber layer and a polyethylene diaphragm which are sequentially stacked; the nanofiltration separation layer comprises an interfacial polymerization product of a water-phase raw material and an oil-phase raw material; the water-phase raw material comprises tannic acid; the electrospinning nanofiber layer comprises an amine group; the nanofiltration separation layer, the electrospinning nanofiber layer and the polyethylene diaphragm are combined through a chemical bond formed by the tannic acid and the amine group, a chemical bond formed by the amine group and the oil-phase raw material and a hydrophobic interaction between the tannic acid and the polyethylene diaphragm. The separation membrane can not only remove heavy metals in water, but also reduce the risk of water production scaling while retaining minerals; and the combination ability between the layers of the separation membrane is strong, the membrane operation stability is high, the thickness is thin, the water flux is large and the production cost is low.

Description

Technical Field

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

[0002] The metallurgical industry generates large amounts of heavy metal pollutants. Due to the significant, persistent, and non-degradable nature of heavy metal pollution, it is crucial to control it at its source. Health experts and practical experience have shown that purified water without minerals is unsuitable for long-term consumption, especially for the elderly, pregnant women, and children. This is because the human body requires minerals for metabolism, and drinking water is one of the main sources of minerals and various trace elements. Therefore, developing a separation membrane or filter element with high water flux, capable of removing heavy metals while retaining minerals, and exhibiting excellent performance stability has broad market value and application prospects.

[0003] The most common water treatment products in current technology are reverse osmosis / nanofiltration membrane filter cartridges. The working principle of a reverse osmosis filter cartridge is to apply a certain pressure to the water, forcing water molecules and ionized mineral elements to pass through the reverse osmosis membrane, while most inorganic salts, including heavy metals, organic matter, bacteria, and viruses in the water cannot pass through the reverse osmosis membrane. Reverse osmosis filter cartridges can effectively remove heavy metals and improve the quality of drinking water, but at the same time, they also remove some minerals from the water.

[0004] Nanofiltration membranes are pressure-driven membranes that are low in cost, have high water flux, and have a high rejection rate for small molecule organic matter and polyvalent salts. They can retain some minerals that are beneficial to the human body, but have a very low rejection rate for heavy metal ions, sulfur and other pollutants.

[0005] 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

[0006] 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 operational stability, thin membrane thickness, large water flux, and low production cost.

[0007] The present invention solves the above-mentioned technical problems through the following technical solution:

[0008] This invention provides a separation membrane comprising a nanofiltration separation layer, an electrospun nanofiber layer, and a polyethylene diaphragm stacked sequentially.

[0009] The nanofiltration separation layer contains interfacial polymerization products of aqueous and oil phase feedstocks;

[0010] The aqueous phase raw material contains tannic acid;

[0011] The electrospun nanofiber layer contains amine groups;

[0012] The nanofiltration separation layer, the electrospun nanofiber layer, and the polyethylene membrane are combined through chemical bonds formed by tannic acid and amine groups, chemical bonds formed by amine groups and oil phase raw materials, and hydrophobic interactions between tannic acid and the polyethylene membrane.

[0013] In this invention, preferably, the separation membrane satisfies one or more of the following conditions:

[0014] The thickness of the separation membrane is 10-30 μm, for example, 10 μm, 20 μm and 30 μm;

[0015] The thickness of the nanofiltration separation layer is 50-80 nm, for example, 53 nm, 68 nm and 80 nm;

[0016] The thickness of the electrospun nanofiber layer is 5-20 μm, for example, 5 μm, 12 μm and 20 μm;

[0017] The thickness of the polyethylene diaphragm is 5-10 μm, for example, 5 μm, 8 μm and 10 μm.

[0018] The present invention also provides a method for preparing a separation membrane, which includes the following steps:

[0019] S1, using electrospinning process to spin a spinning solution formed by polyamine compounds, crosslinking agents and film-forming materials into fibers, using polyethylene diaphragm as receiving substrate to form a nanofiber membrane, which serves as the base membrane;

[0020] S2, 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;

[0021] The aqueous raw material contains tannic acid.

[0022] In this scheme, a hydrophobic interaction exists between polyethylene and tannic acid, and the amine groups of the polyamine compound can chemically react with tannic acid. By utilizing the bonding force between polyethylene and tannic acid, as well as the chemical reaction between tannic acid and amine groups, the bonding force between the polyethylene-based membrane and the nanofiber layer can be strengthened, effectively reducing the degradation of membrane performance after long-term operation and improving the membrane's operational stability.

[0023] In this invention, preferably, step S1 satisfies one or more of the following conditions:

[0024] 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;

[0025] ② The mass fraction of the crosslinking agent is 1-2%, for example, 1%, 1.5% and 2%;

[0026] ③The crosslinking agent includes any one of epichlorohydrin, glutaraldehyde, and glycidyl methacrylate;

[0027] ④ The film-forming material includes any one of polyurethane, polysulfone, polyethersulfone, and polyamide; preferably, the film-forming material is polyurethane.

[0028] ⑤ The mass fraction of the film-forming material is 15-20%, for example, 15%, 17% and 20%;

[0029] ⑥ The polyamine compounds include one or a combination of at least two of tetraethylenepentamine, polyethyleneimine, and chitosan;

[0030] The molecular weight of the polyamine compound is preferably above 100 kDa;

[0031] The polyamine compound preferably contains multiple amine groups, such as primary amine groups;

[0032] ⑦ The raw materials for the spinning solution also include lithium chloride;

[0033] Preferably, the lithium chloride has a mass fraction of 1-3%, for example, 1%, 2% and 3%;

[0034] ⑧ The viscosity of the electrospinning solution is 700-1500 mPa·s.

[0035] In this scheme, the amine groups on the nanofiber layer can form complexes with heavy metal ions, achieving the effect of efficient removal of heavy metals.

[0036] In step S1, preferably, the polyethylene diaphragm satisfies one or more of the following conditions:

[0037] The polyethylene diaphragm is a biaxially oriented polyethylene film;

[0038] The polyethylene diaphragm has a film thickness of 10-30 μm, for example, 10 μm, 20 μm and 30 μm;

[0039] The polyethylene diaphragm has a pore size of 0.2-1 μm, for example, 0.3 μm, 0.5 μm and 1 μm;

[0040] The porosity of the polyethylene diaphragm is 60-80%, for example, 65%, 70%, and 80%.

[0041] In this design, the polyethylene diaphragm is thin, thus reducing the filter cartridge volume and increasing water flux. Furthermore, the polyethylene diaphragm is cheaper than traditional nonwoven fabrics, and while the nonwoven fabrics used in nanofiltration membranes can only be imported, the polyethylene diaphragm can be domestically produced. Therefore, using a polyethylene diaphragm can reduce the production cost of nanofiltration membranes and is beneficial for improving domestic production capabilities.

[0042] In step S1, preferably, the spinning solution is formed by mixing the raw materials and solvent evenly, heating and stirring to obtain the spinning solution;

[0043] Preferably, the time for uniform mixing is 0.5-1 hour, for example, 0.5 hours;

[0044] Preferably, the heating and stirring temperature is 80°C;

[0045] Preferably, the heating and stirring time is 1-2 hours, for example, 1 hour, 1.5 hours and 2 hours.

[0046] In step S1, preferably, the electrospinning process satisfies one or more of the following conditions:

[0047] The electrospinning voltage of the electrospinning process is 70-95kV, for example, 70kV, 80kV and 90kV;

[0048] The distance between the electrode wire and the collector in the electrospinning process is 15-25cm, for example, 15cm, 20cm and 25cm;

[0049] 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;

[0050] 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;

[0051] The temperature of the electrospinning process is 20-40℃, for example, 20℃, 30℃ and 40℃;

[0052] The humidity of the electrospinning process is 20-40%, for example, 20%, 30%, and 40%.

[0053] In step S1, preferably, the nanofiber membrane obtained after electrospinning satisfies one or more of the following conditions:

[0054] The specific surface area of ​​the nanofiber membrane is 500-950 m². 2 / g;

[0055] The porosity of the nanofiber membrane is 60-80%;

[0056] The nanofiber membrane has a fiber diameter of 70-300 nm.

[0057] In this scheme, the high porosity of the nanofiber membrane can fully absorb the solution, thereby reducing the concentration of monomers in the aqueous and oil phases, which significantly reduces the amount of monomers used, reduces the thickness of the nanofiltration separation layer, increases the flux of the separation membrane, reduces environmental pollution, and lowers costs. Furthermore, the high strength of the nanofiber layer can improve the strength and rigidity of the polyethylene substrate, avoiding the phenomenon of membrane winding difficulties caused by the polyethylene substrate being too soft during the preparation of the nanofiltration filter element.

[0058] In this invention, preferably, in step S2, the soaking treatment satisfies one or more of the following conditions:

[0059] The base membrane is immersed in the aqueous solution for 5-10 minutes, for example, 5 minutes, 7 minutes and 10 minutes;

[0060] After the base membrane is immersed in an aqueous solution, excess aqueous solution is removed from the surface of the base membrane.

[0061] The base film is immersed in the oil phase solution for 1-3 minutes, for example, 1 minute, 2 minutes and 3 minutes;

[0062] After the base film is immersed in the oil phase solution, excess oil phase solution is removed from the surface of the base film.

[0063] The aqueous and oil phase solutions can be prepared at room temperature.

[0064] In step S2, 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;

[0065] The temperature of the oven is preferably 60-80°C, for example, 60°C, 70°C and 80°C;

[0066] The reaction time is preferably 5-10 min, for example, 5 min, 7 min and 10 min.

[0067] In step S2, preferably, the aqueous phase solution is an aqueous solution of piperazine and tannic acid, wherein the mass fraction of piperazine is 0.02-0.06%, for example, 0.02%, 0.04%, and 0.06%;

[0068] The mass fraction of the tannic acid is 0.01-0.04%, for example, 0.01%, 0.03%, and 0.04%;

[0069] The pH value of the aqueous solution is 10-11;

[0070] The oil phase solution is a hexane solution of trimesoyl chloride, wherein the mass fraction of trimesoyl chloride is 0.01-0.05%, for example, 0.01%, 0.03%, and 0.05%.

[0071] In this scheme, tannic acid is added to the aqueous solution: 1) By utilizing the binding force between tannic acid and polyethylene, the binding force between tannic acid and oil phase raw materials, and the reactivity of tannic acid and amine groups, the binding force between the polyethylene-based membrane, the electrospun nanofiber layer, and the nanofiltration separation layer is strengthened; 2) As an aqueous phase 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 oil phase raw materials, reducing the thickness of the nanofiltration separation layer, and increasing the membrane flux; 3) Tannic acid molecules have hydrophobic interactions and will aggregate, so some tannic acid is doped into the nanofiltration separation layer in monomer form. On the one hand, this 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.

[0072] 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.

[0073] The present invention further provides a separation membrane, which is prepared by the above-described separation membrane preparation method.

[0074] The present invention also provides a filter element comprising the separation membrane and auxiliary materials as described above.

[0075] The auxiliary materials include a flow guide cloth, a partition net, and a central tube.

[0076] According to a preferred embodiment of the present invention, the separation membrane of this preferred embodiment has a thickness of only 30 μm, and the retention rates of minerals such as potassium ions, sodium ions, lithium ions, and bicarbonates are 31%, 33%, 22%, and 25%, respectively. The removal rates of heavy metals such as lead, cadmium, chromium, and arsenic reach 99.9%, 99.7%, 97.4% or more, and 99.8%, respectively. Furthermore, the membrane also exhibits good performance in removing Ca... 2+ Mg 2+ The retention rates were 10% and 12%, 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:

[0077] A nanofiber membrane is formed by spinning a spinning solution of chitosan, glycidyl methacrylate, polyurethane, and lithium chloride using an electrospinning process. A polyethylene diaphragm is used as the receiving substrate to form the 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.

[0078] The chitosan, glycidyl methacrylate, polyurethane, and lithium chloride are present in mass fractions of 10%, 2%, 20%, and 3%, respectively; the polyethylene membrane has a thickness of 10 μm, a pore size of 1 μm, and a porosity of 80%; the spinning solution is formed by mixing the raw materials and solvent for 0.5 h, heating the solution to 80°C, and stirring for another 2 h 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%.

[0079] 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 0.06% piperazine and 0.04% tannic acid; the oil solution is a 0.05% hexane solution of trimesoyl chloride.

[0080] The positive and progressive effects of this invention are as follows:

[0081] ① Achieving the effect of retaining minerals and removing heavy metals: The separation membrane retains some minerals, while the amine groups on the nanofiber membrane and the tannic acid in the nanofiltration separation layer achieve efficient adsorption and removal of heavy metals. The combined function of these two methods gives the separation membrane the characteristic of selective separation of heavy metals and minerals.

[0082] ② Improve the bonding force between the layers of the separation membrane and improve membrane operation stability: By utilizing the bonding force between tannic acid and polyethylene, the reactivity of tannic acid with amine groups, the reactivity of tannic acid with oil phase feedstock, and the reactivity of amine groups with oil phase feedstock, 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.

[0083] 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

[0084] 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.

[0085] Example 1

[0086] 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.

[0087] 2. Heat the solution to 80°C and stir for 1 hour to obtain the final spinning solution;

[0088] 3. The spinning solution is used to form a nanofiber layer on the surface of a polyethylene membrane through an electrospinning device: the polyethylene membrane has a thickness of 5 μm, a pore size of 0.3 μm, and a porosity of 65%; the spinning voltage is 70 kV, the distance between the electrode thread and the collector is 15 cm, the liquid supply rate is 20 mL / h, the collector speed is 0.015 m / min, the spinning temperature is 20 °C, and the humidity is 20%.

[0089] 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 0.02% piperazine and 0.01% tannic acid.

[0090] 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.

[0091] 6. Place the base membrane from step 5 into a 60°C oven and react for 5 minutes to obtain a separation membrane capable of removing heavy metals while retaining minerals.

[0092] 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.

[0093] Example 2

[0094] 1. Dissolve 7g polyethyleneimine, 1.5g glutaraldehyde, 17g polyurethane, and 2g lithium chloride in 72.5g N,N-dimethylacetamide and stir for 0.5h to obtain a homogeneous solution.

[0095] 2. Heat the solution to 80°C and stir for 1.5 hours to obtain the final spinning solution.

[0096] 3. The spinning solution is used to form a nanofiber layer on the surface of a polyethylene membrane through an electrospinning device: the polyethylene membrane has a thickness of 8 μm, a pore size of 0.5 μm, and a porosity of 70%; the spinning voltage is 80 kV, the distance between the electrode thread and the collector is 20 cm, the liquid supply rate is 100 mL / h, the collector speed is 0.03 m / min, the spinning temperature is 30 °C, and the humidity is 30%.

[0097] 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 0.04% piperazine and 0.03% tannic acid.

[0098] 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 0.03% hexane solution of trimesoyl chloride.

[0099] 6. Place the base membrane from step 5 into a 70°C oven and react for 7 minutes to obtain a 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 3

[0102] 1. Dissolve 10g chitosan, 2g glycidyl methacrylate, 20g polyurethane, and 3g lithium chloride in 65g N,N-dimethylacetamide and stir for 0.5h to obtain a homogeneous solution.

[0103] 2. Heat the solution to 80°C and stir for 2 hours to obtain the final spinning solution.

[0104] 3. The spinning solution is used to form a nanofiber layer on the surface of a polyethylene membrane using an electrospinning device. The polyethylene membrane has a thickness of 10 μm, a pore size of 1 μm, and a porosity of 80%. The spinning voltage is 90 kV, the distance between the electrode thread and the collector is 25 cm, the liquid supply rate is 200 mL / h, the collector speed is 0.05 m / min, the spinning temperature is 40℃, and the humidity is 40%.

[0105] 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 0.06% piperazine and 0.04% tannic acid.

[0106] 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 0.05% hexane solution of trimesoyl chloride.

[0107] 6. Place the base membrane from step 5 into an 80°C oven and react for 10 minutes to obtain a separation membrane capable of removing heavy metals while retaining minerals.

[0108] 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.

[0109] Comparative Example 1

[0110] 1. Immerse the ultrafiltration membrane 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.

[0111] 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.

[0112] 3. Place the base membrane from step 2 into a 60℃ oven and react for 10 minutes to obtain the separation membrane.

[0113] 4. The separation membrane from step 3 is wound together with auxiliary materials such as the flow guide cloth, the separator, and the central tube to form a filter element, thus obtaining the filter element.

[0114] Example 1

[0115] Comparison of heavy metal removal rate, mineral retention rate, membrane thickness, and water flux in Examples 1-3 and Comparative Example 1:

[0116] I. Heavy metal removal rate:

[0117] 1) Preparation of heavy metal solution: Prepare heavy metal solution according to GB30307 requirements;

[0118] 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.

[0119] 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;

[0120] 4) Calculate the heavy metal removal rate:

[0121]

[0122] II. Mineral Retention Rate:

[0123] 1) Prepare mineral solution: Prepare mineral solution according to CB30307 requirements;

[0124] 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.

[0125] 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;

[0126] 4) Calculate the heavy metal removal rate:

[0127]

[0128] III. Film thickness test:

[0129] 1) Thickness test: The thickness of the prepared separation membrane was tested using a thickness gauge.

[0130] IV. Flux Test (Separation Membrane):

[0131] 1) Membrane cutting: Cut the membrane into circular pieces with a diameter of 55mm according to the size of the filter tank;

[0132] 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).

[0133] 3) Flux calculation (denoted as L, unit is L / (m)) 2 *h*bar)):

[0134]

[0135] The specific test results are as follows:

[0136] Table 1 Comparison of Heavy Metal Removal Rates

[0137] Heavy metal removal rate Example 1 Example 2 Example 3 Comparative Example 1 lead 95.1％ 97.2％ 99.9％ 75％ cadmium 93.8％ 98.1％ 99.7％ 80％ chromium 92.7％ 96.8％ >97.4％ 69％ arsenic 93.6％ 99.1％ 99.8％ 71％

[0138] 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 the raw materials in Comparative Example 1 do not contain polyamine compounds or tannic acid.

[0139] Table 2 Comparison of mineral retention rates

[0140] Mineral retention rate* Example 1 Example 2 Example 3 Comparative Example 1 Potassium 39％ 33％ 31％ 29％ calcium 22％ 15％ 10％ 35％ sodium 37％ 32％ 33％ 23％ magnesium 25％ 19％ 12％ 40％ lithium 29％ 25％ 22％ 19％ bicarbonate 32％ 27％ 25％ 20％

[0141] *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.

[0142] 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.

[0143] 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 10%, for Mg 2+ The retention rate was only 12%, which is quite good.

[0144] 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.

[0145] Table 3 Comparison of membrane structure and properties

[0146]

[0147] Note: “——” in the table indicates that the separation membrane does not contain this structure, and therefore the thickness cannot be measured.

[0148] The separation membranes prepared in Examples 1-3 of the present invention comprise a nanofiltration separation layer, an electrospun nanofiber layer, and a polyethylene membrane stacked sequentially; the nanofiltration separation layer contains an interfacial polymerization product of tannic acid and trimesoyl chloride; the electrospun nanofiber layer contains amine groups; the nanofiltration separation layer, the electrospun nanofiber layer, and the polyethylene membrane are bonded together by chemical bonds formed between tannic acid and amine groups, chemical bonds formed between amine groups and trimesoyl chloride, and hydrophobic interactions between tannic acid and the polyethylene membrane.

[0149] 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.

[0150] 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.

[0151] 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, It includes a nanofiltration separation layer, an electrospun nanofiber layer, and a polyethylene membrane stacked sequentially; The nanofiltration separation layer contains interfacial polymerization products of aqueous and oil phase feedstocks; The aqueous phase raw material contains tannic acid; The electrospun nanofiber layer contains amine groups; The nanofiltration separation layer, the electrospun nanofiber layer, and the polyethylene membrane are combined through chemical bonds formed by tannic acid and amine groups, chemical bonds formed by amine groups and oil phase raw materials, and hydrophobic interactions between tannic acid and the polyethylene membrane. The amine group is derived from polyamine compounds, which include 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 10-30 μm; The thickness of the nanofiltration separation layer is 50-80 nm; The thickness of the electrospun nanofiber layer is 5-20 μm; The thickness of the polyethylene diaphragm is 5-10 μm.

3. The separation membrane according to claim 2, characterized in that, The separation membrane satisfies one or more of the following conditions: The thickness of the separation membrane is 10 μm, 20 μm or 30 μm; The thickness of the nanofiltration separation layer is 53 nm, 68 nm, or 80 nm. The thickness of the electrospun nanofiber layer is 5 μm, 12 μm or 20 μm; The thickness of the polyethylene diaphragm is 5 μm, 8 μm, or 10 μm.

4. A method for preparing a separation membrane, characterized in that, It includes the following steps: S1, using electrospinning technology to spin a spinning solution formed by polyamine compounds, crosslinking agents and film-forming materials into fibers, using a polyethylene diaphragm as the receiving substrate to form a nanofiber membrane, which serves as the base membrane; the polyamine compounds include one or a combination of at least two of tetraethylenepentamine, polyethyleneimine and chitosan; S2, 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; The aqueous raw material contains tannic acid.

5. The preparation method according to claim 4, characterized in that, In step S1, the mass fraction of the polyamine compound is 5%-10% based on the mass fraction of each component relative to the total mass of the spinning solution. And / or, the mass fraction of the crosslinking agent is 1%-2%; And / or, the crosslinking agent includes any one of epichlorohydrin, glutaraldehyde, and glycidyl methacrylate; And / or, the film-forming material includes any 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 for the spinning solution also include lithium chloride; And / or, the viscosity of the spinning solution is 700-1500 mPa·s.

6. The preparation method according to claim 5, characterized in that, In step S1, the mass fraction of the polyamine compound is 5%, 7%, or 10%.

7. The preparation method according to claim 5, characterized in that, The mass fraction of the crosslinking agent is 1%, 1.5%, or 2%.

8. The preparation method according to claim 5, characterized in that, The film-forming material is polyurethane.

9. The preparation method according to claim 5, characterized in that, The mass fraction of the film-forming material is 15%, 17%, or 20%.

10. The preparation method according to claim 5, characterized in that, The polyamine compound has a molecular weight of 100 kDa or higher.

11. The preparation method according to claim 5, characterized in that, The polyamine compounds contain multiple amine groups.

12. The preparation method according to claim 11, characterized in that, The polyamine compounds contain multiple primary amine groups.

13. The preparation method according to claim 5, characterized in that, The mass fraction of the lithium chloride is 1%-3%.

14. The preparation method according to claim 13, characterized in that, The mass fraction of the lithium chloride is 1%, 2%, or 3%.

15. The preparation method according to claim 4, characterized in that, In step S1, the polyethylene diaphragm satisfies one or more of the following conditions: The polyethylene diaphragm is a biaxially oriented polyethylene film; The polyethylene diaphragm has a film thickness of 10-30 μm; The pore size of the polyethylene diaphragm is 0.2-1 μm; The porosity of the polyethylene diaphragm is 60%-80%; And / or, the spinning solution is formed by mixing each raw material with a solvent evenly, heating and stirring to obtain the spinning solution.

16. The preparation method according to claim 15, characterized in that, In step S1, the polyethylene diaphragm satisfies one or more of the following conditions: The polyethylene diaphragm has a film thickness of 10 μm, 20 μm, or 30 μm; The pore size of the polyethylene diaphragm is 0.3 μm, 0.5 μm, or 1 μm; The porosity of the polyethylene diaphragm is 65%, 70%, or 80%.

17. The preparation method according to claim 15, characterized in that, The time for uniform mixing is 0.5-1 hour.

18. The preparation method according to claim 15, characterized in that, The heating and stirring temperature is 80°C.

19. The preparation method according to claim 15, characterized in that, The heating and stirring time is 1-2 hours.

20. The preparation method according to claim 19, characterized in that, The heating and stirring time is 1 hour, 1.5 hours, or 2 hours.

21. The preparation method according to claim 4, characterized in that, In step S1, the electrospinning process satisfies one or more of the following conditions: The electrospinning voltage of the process is 70-95kV; The distance between the electrode wire and the collector in the electrospinning process is 15-25cm; The liquid supply rate for the electrospinning process is 5-200 mL / h; The collector speed in the electrospinning process is 0.01-0.05 m / 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 500-950 m². 2 / g; The porosity of the nanofiber membrane is 60-80%; The nanofiber membrane has a fiber diameter of 70-300 nm.

22. The preparation method according to claim 21, characterized in that, In step S1, the electrospinning process satisfies one or more of the following conditions: The electrospinning voltage of the 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 20 mL / h, 100 mL / h, or 200 mL / h; The collector speed in the electrospinning process is 0.015 m / min, 0.03 m / min, or 0.05 m / min; The temperature of the electrospinning process is 20°C, 30°C, or 40°C. The humidity of the electrospinning process is 20%, 30%, or 40%.

23. The preparation method according to claim 4, characterized in that, The soaking treatment satisfies one or more of the following conditions: The base membrane is immersed in the aqueous solution for 5-10 minutes. After the base membrane is immersed in an aqueous solution, excess aqueous solution is removed from the surface of the base membrane. The base film is immersed in the oil phase solution for 1-3 minutes; After the base film is immersed in the oil phase solution, excess oil phase solution is removed from the surface of the base film. 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.

24. The preparation method according to claim 23, characterized in that, The base membrane is immersed in the aqueous solution for 5 min, 7 min, or 10 min.

25. The preparation method according to claim 23, characterized in that, The base film is immersed in the oil phase solution for 1 min, 2 min, or 3 min.

26. The preparation method according to claim 23, characterized in that, The temperature of the oven is 60-80℃.

27. The preparation method according to claim 26, characterized in that, The temperature of the oven is 60°C, 70°C, or 80°C.

28. The preparation method according to claim 23, characterized in that, The reaction time is 5-10 minutes.

29. The preparation method according to claim 28, characterized in that, The reaction time is 5 min, 7 min, or 10 min.

30. The preparation method according to claim 4, characterized in that, In step S2, the aqueous solution is an aqueous solution of piperazine and tannic acid, wherein the mass fraction of piperazine is 0.02%-0.06%. The mass fraction of the tannic acid is 0.01%-0.04%; And / or, the pH value of the aqueous 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%-0.05%.

31. The preparation method according to claim 30, characterized in that, The piperazine has a mass fraction of 0.02%, 0.04%, or 0.06%.

32. The preparation method according to claim 30, characterized in that, The mass fraction of the tannic acid is 0.01%, 0.03%, or 0.04%.

33. The preparation method according to claim 30, characterized in that, The mass fraction of the pyromellitic chloroformyl chloride is 0.01%, 0.03%, or 0.05%.

34. A separation membrane, characterized in that, The separation membrane is prepared by the preparation method according to any one of claims 4 to 33.

35. A filter element, characterized in that, It includes the separation membrane and auxiliary materials as described in any one of claims 1 to 3 and claim 34; The auxiliary materials include a flow guide cloth, a partition net, and a central tube.

Images