Filter element and preparation method thereof

Abstract

The invention discloses a filter element and a preparation method thereof, the filter element comprises an inner-layer annular column and an outer-layer annular column, the annular columns are made of fibers, the filter element is characterized in that the outer-layer annular column is a concentric cylinder and is composed of an inner core and a skin layer, and the inner core and the skin layer are connected through an amido bond; and the thickness of the skin layer is 5-11 nm. The preparation method of the filter element is simple, a melt-blowing and modifying mode can be adopted, and the cost of the filter element is low; in the preparation process, the adsorption material on the fiber can adsorb heavy metals, so that the filter element efficiently removes the heavy metals, the cross-linking material can improve the loading capacity of the adsorption material on the surface of the fiber, the removal life of the filter element on the heavy metals is prolonged, and the adsorption material and the fiber are connected through chemical bonds, so that the filter element is more stable and longer in service life.

Description

Technical Field

[0001] The present invention relates to a filter element and a preparation method thereof. Background Art

[0002] Currently, the main types of filter materials for removing heavy metals are as follows: ion exchange resin filter elements, where modified ion exchange resins have a certain function of removing heavy metals; separation membrane filter elements, which are prepared by a phase inversion method to introduce an adsorbent onto the surface of a separation membrane (such as a hollow fiber membrane) to achieve the function of removing heavy metals; reverse osmosis membranes that can remove heavy metal ions by pore size sieving; or activated carbon-based filter elements, which achieve the function of removing heavy metals by modifying carbon powder or introducing an adsorbent during the sintering process.

[0003] However, the above several types of filter materials for removing heavy metals all have problems: for ion exchange resins, due to the large gaps between ion exchange resins, water easily flows through the gaps between the resins, and the effective components of ion exchange resins are mainly concentrated inside the resins, so the heavy metal removal efficiency of ion exchange resin filter elements is not high; for separation membrane filter elements: 1) the preparation process of separation membranes (hollow fiber membrane chromatography) with heavy metal adsorption and removal functions is complex; 2) the preparation process of reverse osmosis filter elements is complex and costly, and the flux of the filter elements is low; for activated carbon-based ones, activated carbon and the adsorbent are mainly bonded by physical bonds, with weak bonding ability, there is a problem of adsorbent loss, and there is a risk in the performance stability of the filter element.

[0004] It can be seen that the common problems of existing filter materials capable of removing heavy metals are: low heavy metal removal efficiency, complex preparation process, high filter element preparation cost, low flow rate, low stability, etc. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a filter element with a simple preparation method, low cost, high heavy metal removal rate, stability, and longer service life in view of the above-mentioned prior art.

[0006] One of the technical solutions adopted by the present invention to solve the above technical problems is: a filter element, including an inner layer circular cylinder and an outer layer circular cylinder, the material of the circular cylinder is fiber, the outer layer circular cylinder is a concentric cylinder, composed of an inner core and a cortex, and the inner core and the cortex are connected by an amide bond; the thickness of the cortex is 5 - 11 nm.

[0007] In the present invention, the thickness of the cortex can be 5.3 nm or 10.2 nm.

[0008] In the present invention, the fiber raw material of the inner layer circular cylinder is polypropylene and / or polyethylene.

[0009] The inner layer uses the above-mentioned fiber raw materials as the support layer, which avoids the damage of the filter element during the manufacturing process. A support layer needs to be set during the meltblowing process. Otherwise, the outer ring-shaped columnar fibers cannot directly manufacture the ring-shaped columnar filter element by meltblowing.

[0010] In the present invention, the core fiber raw material of the outer ring column is one or more of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate.

[0011] In the present invention, the diameter of the core is 10-15 μm.

[0012] In the present invention, the inner diameter of the inner ring column is 5-30 mm, preferably 15-30 mm, such as 15 mm or 30 mm.

[0013] In the present invention, the outer diameter of the inner ring column is 15-50 mm, preferably 30-50 mm, such as 30 mm or 50 mm.

[0014] In the present invention, the inner diameter of the outer ring column is 15-50 mm, preferably 30-50 mm, such as 30 mm or 50 mm.

[0015] In the present invention, the outer diameter of the outer ring column is 60-90 mm, such as 60 mm or 90 mm.

[0016] In the present invention, the fibers of the inner ring column and the fibers of the outer ring column are combined by melt bonding and friction.

[0017] In the present invention, the diameter of the fibers of the inner ring column is 3-10 μm, preferably 5-10 μm, such as 5 μm or 10 μm.

[0018] In the present invention, the diameter of the fibers of the outer ring column is 8-15 μm, preferably 10-15 μm, such as 10 μm or 15 μm.

[0019] In the present invention, the isoelectric point of the fibers of the inner ring column is 4, and it is negatively charged in water with a pH of 7.

[0020] In the present invention, the isoelectric point of the fibers of the outer ring column is 7-9, and it is positively charged in water with a pH of 7.

[0021] The isoelectric point is the pH value at which a molecule has no net charge on its surface. The charge carried by zwitterions changes with the pH value of the solution. When the positive and negative charge values of the zwitterions are equal, the pH value of the solution is its isoelectric point.

[0022] In the present invention, the porosity at the position closest to the center of the inner ring column is 20-30%, such as 20% or 30%.

[0023] In the present invention, the pore diameter at the position closest to the center of the circle in the inner circular cylindrical column is 1 to 3 μm, such as 2 μm or 3 μm.

[0024] In the present invention, the porosity at the position farthest from the center of the circle in the inner circular cylindrical column is 40 to 70%, preferably 60% to 70%, such as 60% or 70%.

[0025] In the present invention, the pore diameter at the position farthest from the center of the circle in the inner circular cylindrical column is 10 to 15 μm, preferably 13 to 15 μm, such as 13 μm or 15 μm.

[0026] In the present invention, the porosity at the position closest to the center of the circle in the outer circular cylindrical column is 40 to 60%, such as 50% or 60%.

[0027] In the present invention, the pore diameter at the position closest to the center of the circle in the outer circular cylindrical column is 5 to 10 μm, such as 7 μm or 10 μm.

[0028] In the present invention, the porosity at the position farthest from the center of the circle in the outer circular cylindrical column is 70 to 90%, such as 80% or 90%.

[0029] In the present invention, the pore diameter at the position farthest from the center of the circle in the outer circular cylindrical column is 15 to 20 μm, such as 17 μm or 20 μm.

[0030] In the present invention, as the distance from the center of the circle of the outer circular cylindrical column and the inner circular cylindrical column gradually decreases, the density of the fibers increases linearly;

[0031] The density ρ of the fibers refers to the percentage of the fiber volume in the overall volume of the filter element. The porosity is denoted as δ, the distance from the fiber to the inner circle is defined as x, in unit of mm, and the thickness of the circular cylindrical column is b, in unit of mm; the density of the fibers satisfies the following conditions:

[0032] In the present invention, the density of the fibers is ρ = (1 - δ) × 100%,

[0033] When x = 0, the distance from the fiber to the inner circle is defined as 0, and this is the innermost side of the circular cylindrical column.

[0034] In the present invention, the change of the density of the fibers with the distance is ρ = ρ1 - ((ρ1 - ρ2) / b) × x.

[0035] In a preferred embodiment of the present invention, when the outer diameter of the outer circular cylindrical column is 60 mm, the inner diameter is 30 mm, the fiber density at the position close to the center of the circle is 50%, and the fiber density at the position far from the center of the circle is 20%, starting from the position of the circular cylindrical column close to the center of the circle, the fiber density at the distance from the starting point is ρ = (50 - x) × 100%.

[0036] In the present invention, the density of the fibers near the center of the circle of the outer ring column is 40% - 60%, such as 40% or 50%.

[0037] In the present invention, the density of the fibers far from the center of the circle of the outer ring column is 10% - 30%, such as 10% or 20%.

[0038] In the present invention, the density of the fibers near the center of the circle of the inner ring column is 70% - 80%, such as 70% or 80%.

[0039] In the present invention, the density of the fibers far from the center of the circle of the inner ring column is 30% - 60%, such as 30% or 40%. The second technical solution adopted by the present invention to solve the above technical problems is: a method for preparing a filter element, wherein the inner ring column and the outer ring column are prepared from fibers by a meltblowing process, and the outer ring column is wound around the outside of the inner ring column type.

[0040] The outer ring column type is composed of a core and a cortex, and the core and the cortex are connected by an amide. The cortex includes the following preparation steps:

[0041] S1: Treat the double-layer structure having the inner filter element and the outer ring column type with plasma;

[0042] S2: Immerse the plasma-treated double-layer structure in a modification solution; the modification solution is an aqueous mixed solution of an adsorption material and a crosslinking material, and the adsorption material is chitosan and / or polyethyleneimine;

[0043] S3: Clean and dry the filter element obtained in step S2.

[0044] After plasma treatment, active functional groups are introduced on the surface of the fiber material, which can greatly increase the loading amount of the adsorption material on the fiber surface, thereby increasing the removal life of heavy metals by the filter element.

[0045] In the present invention, the concentration of the adsorption material is 1% - 5%, preferably 3% - 5%, such as 3% or 5%.

[0046] In the present invention, the concentration of the crosslinking material is 0.5% - 1%, such as 0.7% or 1%.

[0047] The preparation steps of the cortex satisfy the following conditions:

[0048] The time of the plasma treatment is 10 - 120 s, preferably 60 - 120 s, such as 60 s or 120 s.

[0049] The crosslinking material is glycidyl acrylate and / or glycerol glycidyl ether.

[0050] The crosslinking material can increase the loading amount of the adsorbent material on the fiber surface, thereby increasing the removal lifespan of heavy metals by the filter element.

[0051] The soaking time is 0.5 - 2 h, such as 1 h or 2 h.

[0052] The soaking temperature is 60 - 80 °C, such as 70 °C or 80 °C.

[0053] In the present invention, through plasma treatment and adding a crosslinking material to the modification solution, a uniform, dense and cortical structure with a certain thickness is finally formed on the fiber surface, thereby achieving a high removal lifespan of heavy metals.

[0054] The third technical solution adopted by the present invention to solve the above technical problems is: a filter element prepared by the preparation method of the filter element as described above.

[0055] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be arbitrarily combined to obtain various preferred examples of the present invention.

[0056] The reagents and raw materials used in the present invention are all commercially available.

[0057] The positive and progressive effects of the present invention are as follows:

[0058] (1) The preparation method of the filter element of the present invention is simple, and the meltblown + modification method can be adopted, and the cost of the filter element is low; during the preparation process, the adsorbent material on the fiber can adsorb heavy metals, so as to achieve efficient removal of heavy metals by the filter element. The crosslinking material can increase the loading amount of the adsorbent material on the fiber surface, thereby increasing the removal lifespan of heavy metals by the filter element, and the adsorbent material and the fiber are connected by chemical bonds, which is more stable and has a longer lifespan.

[0059] (2) For the outer cylindrical ring and the inner cylindrical ring of the present invention, as the distance from the center of the circle gradually decreases, the density of the fibers increases linearly. Due to the "outer sparse and inner dense" structure, heavy metals can be fully adsorbed. On the one hand, the removal rate of heavy metals is increased; on the other hand, the adsorption capacity of heavy metals can be increased, and the service life can be extended. Description of the Drawings

[0060] Figure 1 It is the XPS diagram of the outer layer fibers of the filter element in Example 2 before modification;

[0061] Figure 2 It is the XPS diagram of the outer layer fibers of the filter element in Example 2 after modification;

[0062] Figure 3 It is the zeta potential diagram of the outer layer fibers of the filter element in Example 2 before and after modification. Detailed Embodiments

[0063] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0064] In the following examples, the fiber density (ρ) is the percentage of the fiber volume in the overall volume of the filter element, the porosity is denoted as δ, the distance from the fiber to the inner circle is defined as x (x = 0 means the innermost side of the circular cylinder), the unit is mm, and the thickness of the circular cylinder is b, the unit is mm. The fiber density and its variation with distance satisfy the following rules:

[0065] 1) The fiber density is ρ = (1 - δ) × 100%;

[0066] 2) The variation of the fiber density with distance: ρ = ρ_1 - ((ρ_1 - ρ_2) / b) × x.

[0067] Example 1

[0068] Heat the polypropylene to 200 - 250 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-sized fibers through a spinneret; then receive the ejected micron-sized fibers through a rotating screw, so that the fibers form an inner cylindrical ring on the screw with an inner diameter of 15 mm, an outer diameter of 30 mm, an inner layer fiber diameter of 5 μm, a pore diameter of 2 μm and a porosity of 20% and a fiber density of 80% near the center of the circle, and a pore diameter of 13 μm, a porosity of 60% and a fiber density of 40% far from the center of the circle.

[0069] Heat the polytrimethylene terephthalate to 250 - 300 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-sized fibers through a spinneret; then receive the ejected micron-sized fibers through a rotating screw that has formed the inner cylindrical ring, so that the fibers form the inner core of the outer cylindrical ring on the surface of the inner cylindrical ring.

[0070] The outer cylindrical ring is a concentric cylinder, composed of an inner core and a cortex, and the inner core and the cortex are connected by an amide bond. The cortex includes the following preparation steps:

[0071] S1: Treat the double-layer structure with the inner circular cylinder and the outer circular cylinder with plasma for 60 s;

[0072] S2: Immerse the plasma-treated double-layer structure in a solution of 3% chitosan and 0.7% glycerol glycidyl ether, and soak at 70 °C for 1 h;

[0073] S3: Remove the soaked filter element obtained in step S2, wash it clean with pure water, and dry it at room temperature to obtain a cortex with a thickness of 5.3 nm.

[0074] The inner diameter of the outer cylindrical ring is 30 mm, the outer diameter is 60 mm, the outer fiber diameter is 10 μm, the pore diameter near the center is 7 μm, the porosity is 50%, and the fiber density is 50%. The pore diameter far from the center is 17 μm, the porosity is 80%, and the fiber density is 20%.

[0075] Example 2

[0076] The polypropylene is heated to 200 - 250 °C to make the raw material in a molten state, and the molten raw material is extruded by a screw extruder and micron-sized fibers are ejected through a spinneret; then the ejected micron-sized fibers are received by a rotating screw to form an inner cylindrical ring with an inner diameter of 30 mm and an outer diameter of 50 mm on the screw. The inner fiber diameter is 10 μm, the pore diameter near the center is 3 μm, the porosity is 30%, the fiber density is 70%, the pore diameter far from the center is 15 μm, the porosity is 70%, and the fiber density is 30%.

[0077] The polybutylene terephthalate is heated to 250 - 300 °C to make the raw material in a molten state, and the molten raw material is extruded by a screw extruder and micron-sized fibers are ejected through a spinneret; then the ejected micron-sized fibers are received by a rotating screw that has already formed the inner cylindrical ring of the cylindrical ring to form the inner core of the outer cylindrical ring on the surface of the inner cylindrical ring.

[0078] The outer cylindrical ring is a concentric cylinder, composed of an inner core and a cortex, and the inner core and the cortex are connected by amide bonds. The cortex includes the following preparation steps:

[0079] S1: The double-layer structure having the inner cylindrical ring and the outer cylindrical ring is treated with plasma for 120 s;

[0080] S2: The double-layer structure after the plasma treatment is immersed in a solution of 5% polyethyleneimine and 1% glycerol glycidyl ether, and immersed at 80 °C for 2 h;

[0081] S3: The immersed filter element obtained in step S2 is removed, washed clean with pure water, and dried at room temperature to obtain a cortex with a thickness of 10.2 nm.

[0082] The inner diameter of the outer cylindrical ring is 50 mm, the outer diameter is 90 mm, the outer fiber diameter is 15 μm, the pore diameter near the center is 10 μm, the porosity is 60%, the fiber density is 40%, the pore diameter far from the center is 20 μm, the porosity is 90%, and the fiber density is 10%.

[0083] Comparative Example 1

[0084] Heat the polypropylene to 200 - 250 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-sized fibers through a spinneret; then receive the ejected micron-sized fibers through a rotating screw, so that the fibers form an inner cylindrical ring on the screw with an inner diameter of 30 mm, an outer diameter of 50 mm, an inner layer fiber diameter of 10 μm, a pore diameter of 3 μm and a porosity of 30% near the center of the circle, and a pore diameter of 15 μm and a porosity of 70% far from the center of the circle.

[0085] Heat the polybutylene terephthalate to 250 - 300 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-sized fibers through a spinneret; then receive the ejected micron-sized fibers through a rotating screw that has formed the inner cylindrical ring, so that the fibers form the inner core of the outer cylindrical ring on the surface of the inner cylindrical ring.

[0086] The outer cylindrical ring is a concentric cylinder, composed of an inner core and a cortex, and the inner core and the cortex are connected by an amide bond. The cortex includes the following preparation steps:

[0087] S1: Treat the double-layer structure with the inner cylindrical ring and the outer cylindrical ring with plasma for 120 s;

[0088] S2: Immerse the plasma-treated double-layer structure in polyethyleneimine with a concentration of 5% and soak it at 80 °C for 2 h;

[0089] S3: Remove the soaked filter element obtained in step S2, wash it clean with pure water, and dry it at room temperature to obtain a cortex with a thickness of 3.7 nm.

[0090] The inner diameter of the outer cylindrical ring is 50 mm, the outer diameter is 90 mm, the outer layer fiber diameter is 15 μm, the pore diameter near the center of the circle is 10 μm and the porosity is 60%, and the pore diameter far from the center of the circle is 20 μm and the porosity is 90%.

[0091] Comparative Example 2

[0092] Heat the polypropylene to 200 - 250 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-sized fibers through a spinneret; then receive the ejected micron-sized fibers through a rotating screw, so that the fibers form an inner cylindrical ring on the screw with an inner diameter of 30 mm, an outer diameter of 50 mm, an inner layer fiber diameter of 10 μm, a pore diameter of 3 μm and a porosity of 30% near the center of the circle, and a pore diameter of 15 μm and a porosity of 70% far from the center of the circle.

[0093] Heat polybutylene terephthalate to 250 - 300 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-scale fibers through a spinneret; then receive the ejected micron-scale fibers through a rotating screw that has formed an inner cylindrical ring, so that the fibers form an inner core of an outer cylindrical ring on the surface of the inner cylindrical ring.

[0094] The outer cylindrical ring is a concentric cylinder, composed of an inner core and a cortex, and the inner core and the cortex are connected by an amide bond. The cortex includes the following preparation steps:

[0095] Directly immerse the double-layer structure with the inner cylindrical ring and the outer cylindrical ring into polyethyleneimine with a concentration of 5%, and immerse it at 80 °C for 2 h;

[0096] Remove the soaked filter element obtained, wash it clean with pure water, and dry it at room temperature to obtain a cortex with a thickness of 1.2 nm.

[0097] The inner diameter of the outer cylindrical ring is 50 mm, the outer diameter is 90 mm, the outer fiber diameter is 15 μm, the pore diameter near the center of the circle is 10 μm, the porosity is 60%, the pore diameter far from the center of the circle is 20 μm, and the porosity is 90%.

[0098] Comparative Example 3

[0099] Heat polypropylene to 200 - 250 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-scale fibers through a spinneret; then receive the ejected micron-scale fibers through a rotating screw, so that the fibers form an inner cylindrical ring on the screw with an inner diameter of 30 mm, an outer diameter of 50 mm, an inner fiber diameter of 10 μm, a pore diameter near the center of the circle of 3 μm, a porosity of 30%, a pore diameter far from the center of the circle of 15 μm, and a porosity of 70%.

[0100] Heat polybutylene terephthalate to 250 - 300 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-scale fibers through a spinneret; then receive the ejected micron-scale fibers through a rotating screw that has formed an inner cylindrical ring, so that the fibers form an outer cylindrical ring on the surface of the inner cylindrical ring.

[0101] The outer cylindrical ring is a concentric cylinder, composed of an inner core and a cortex, and the inner core and the cortex are connected by an amide bond. The cortex includes the following preparation steps:

[0102] S1: Treat the double-layer structure with the inner cylindrical ring and the outer cylindrical ring with plasma for 120 s;

[0103] S2: Immerse the double-layer structure after plasma treatment into a solution containing 5% polyethyleneimine and 1% glycidyl ether of glycerol at 80 °C for 2 h.

[0104] S3: Remove the immersed filter element obtained in step S2, wash it thoroughly with pure water, and dry it at room temperature to obtain a skin layer with a thickness of 9.9 nm.

[0105] The inner diameter of the outer cylindrical ring is 50 mm, the outer diameter is 90 mm, the inner layer fiber diameter is 50 μm, the pore diameter near the center is 16 μm, and the porosity is 35%. The pore diameter far from the center is 35 μm, and the porosity is 58%.

[0106] Comparative Example 4

[0107] Heat polyethylene to 200 - 250 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-sized fibers through a spinneret; then receive the ejected micron-sized fibers with a rotating screw to form an inner cylindrical ring on the screw with an inner diameter of 5 mm, an outer diameter of 15 mm, an inner layer fiber diameter of 3 μm, a pore diameter near the center of 1 μm, a porosity of 20%, a pore diameter far from the center of 10 μm, and a porosity of 40%.

[0108] Heat polyethylene terephthalate to 250 - 300 °C to make the raw material in a molten state, extrude the molten raw material with a screw extruder, and eject micron-sized fibers through a spinneret; then receive the ejected micron-sized fibers with a rotating screw that has already formed the inner cylindrical ring to form an outer cylindrical ring on the surface of the inner cylindrical ring.

[0109] The outer cylindrical ring is a concentric cylinder, composed of a core and a skin layer, and the core and the skin layer are connected by amide bonds. The skin layer includes the following preparation steps:

[0110] S1: Treat the double-layer structure with the inner cylindrical ring and the outer cylindrical ring type with plasma for 10 s.

[0111] S2: Immerse the double-layer structure after plasma treatment into a solution containing 1% tetraethylenepentamine and 0.5% glycidyl acrylate at 60 °C for 0.5 h.

[0112] S3: Remove the immersed filter element obtained in step S2, wash it thoroughly with pure water, and dry it at room temperature to obtain a skin layer with a thickness of 2.5 nm.

[0113] The inner diameter of the outer cylindrical ring is 15 mm, the outer diameter is 60 mm, the diameter of the outer layer fibers is 8 μm, the pore diameter near the center of the circle is 5 μm, the porosity is 40%, the pore diameter far from the center of the circle is 15 μm, and the porosity is 70%.

[0114] Table 1 shows the process conditions of Examples 1 and 2 and Comparative Examples 1 to 5 and the corresponding specific parameters of the products.

[0115] Table 1

[0116]

[0117]

[0118] Remarks: The pores 1 and 2 in the inner layer refer to the pores near the center of the circle and the pores far from the center of the circle respectively; the pores 1 and 2 in the outer layer refer to the pores near the center of the circle and the pores far from the center of the circle respectively.

[0119] Effect Example

[0120] I. Heavy metal removal rate:

[0121] 1) Prepare the heavy metal solution: Prepare the heavy metal solution according to the requirements of GB30307;

[0122] 2) Test the heavy metal removal effect: Pass the prepared heavy metal solution into the filter element, and take 10 ml of the filtrate after stabilization; at the same time, take 10 ml of the original solution;

[0123] 3) Test the heavy metal solution concentration: Use an atomic absorption spectrometer to test the heavy metal concentrations of the filtrate and the original solution, denoted as C1 and C2;

[0124] 4) Calculate the heavy metal removal rate:

[0125] Heavy metal removal rate = (1 - C1 / C2) * 100%

[0126] II. Lifetime of heavy metal removal

[0127] Adopt the test method of heavy metal removal rate to conduct a full-course spiking test. When the heavy metal removal rate is lower than 80%, it means the end of the lifetime. At this time, the water passing volume is the lifetime of heavy metal removal.

[0128] III. Surface element analysis

[0129] The basic steps are as follows: 1. Pretreat the sample to remove surface contaminants. 2. Install the sample in the test equipment. 3. Excite the electrons on the surface of the sample through X-ray photon irradiation and collect relevant information for surface analysis.

[0130] IV. Test of the surface charge property of the material

[0131] The main method for testing the zeta potential on the fiber surface is the streaming potential method. The specific operation is as follows:

[0132] 1. Assemble the membrane sample to form a capillary flow channel with a height of 100 μm.

[0133] 2. Use the Anton Paar SurPASS 3 instrument to measure the streaming potential Ustr of the solution.

[0134] 3. Calculate the zeta potential using the dUstr / dΔp ratio.

[0135] 1) Analyze the filter element material

[0136] Before and after the modification of the outer layer fibers of the filter element (before and after the modification in Example 2), the analysis results of the chemical composition on the fiber surface are as Figure 1 and Figure 2 shown. It can be seen from the figure that before and after the modification, the N element content on the surface of the outer layer fibers has increased significantly, by 5.95% (as shown in Table 2), which is mainly due to the N element in the adsorbent material (polyethyleneimine).

[0137] Table 2 Analysis results of the element content of the outer layer fibers

[0138]

[0139]

[0140] Before and after the modification of the outer layer fibers of the filter element (before and after the modification in Example 2), the charge property results on the fiber surface are as Figure 3 shown. It can be seen from the figure that after the modification, due to the loading of the adsorbent material on the fiber surface, the positive charge property has increased significantly, and the isoelectric point of the material surface has increased from 4.6 before the modification to 8.3 after the modification (as shown in Table 3), which is mainly due to the obvious positive charge carried by the adsorbent material (polyethyleneimine).

[0141] Table 3 Charge property of the outer layer fibers

[0142] Fiber chargeability Outer fiber inner core Outer fiber cortex Isoelectric point (IEP) 4.6 8.3

[0143] 2) Analyze the heavy metal adsorption capacity and lifespan of the filter element

[0144] a. Heavy metal adsorption capacity of the filter element

[0145] The removal capabilities of different heavy metals by different examples and comparative examples are shown in Table 4.

[0146] Table 4 Removal effects of heavy metals by the filter elements of the examples and comparative examples

[0147] Heavy metal Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Lead 99.10％ 99.90％ 99.30％ 98.90％ 98.2％ 97.80％ 98.9％ Cadmium 99.70％ 99.80％ 99.20％ 99.60％ 97.5％ 98.60％ 99.1％ Chromium >97.4％ >97.4％ >97.3％ >97.2％ 95.9％ 96.10％ >97.4％

[0148] b. Heavy metal removal life of the filter element

[0149] The removal lives (amount of heavy metal solution removed) of different examples and comparative examples for heavy metals (such as cadmium) are shown in Table 5.

[0150] Table 5 Life of filter elements in examples and comparative examples for heavy metal removal

[0151] Heavy metal Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Lifetime / t 4.7 15.3 3.2 0.8 1.9 1.9 2.8

[0152] The difference between Comparative Example 2 and Example 2 lies in that: the double-layer structure of the inner-layer circular cylinder and the outer-layer circular cylinder is not subjected to plasma treatment, and at the same time, the modifier solution does not contain a cross-linking agent. At this time, the skin layer thickness of Comparative Example 2 is 1.2 nm, and the skin layer thickness of Example 2 is 10.2 nm. From the above analysis of the heavy metal adsorption capacity and life of the filter element, it can be seen that the removal degree of lead by the filter element of Comparative Example 2 has decreased, especially the life of the filter element of Comparative Example 2 for heavy metal removal has been greatly reduced, from 15.3 t in Example 2 to 0.8 t, a reduction of about 19 times. It can be seen that during the preparation process of the filter element, plasma treatment and the addition of cross-linked materials are beneficial to form a dense skin layer on the fiber surface, greatly extending the service life of the filter element.

[0153] The difference between Comparative Example 5 and Example 1 lies in that: the overall fiber density in the outer-layer circular cylinder is uniform. In comparison, there is not much difference in the heavy metal removal rate between the technical solutions of Comparative Example 5 and Example 1, and the main difference lies in the heavy metal removal life. This is because the "outer loose and inner tight" structure can fully adsorb heavy metals, thereby improving the overall adsorption and removal effect.

Claims

1. A filter element, comprising an inner-layer circular cylinder and an outer-layer circular cylinder, wherein the inner-layer circular cylinder and the outer-layer circular cylinder are made of fiber, and is characterized in that: The outer circular cylindrical ring is a concentric circular cylindrical ring, which is composed of a core and a cortex. The core and the cortex are connected by amide bonds; the thickness of the cortex is 5-11 nm.

2. The filter element according to claim 1, wherein The fiber raw material of the inner circular cylindrical ring is polypropylene and / or polyethylene; And / or, the core fiber raw material of the outer circular cylindrical ring is one or more of polyethylene terephthalate, polytrimethylene terephthalate and polybutylene terephthalate.

3. The filter element according to claim 1, characterized in that, The diameter of the core is 10-15 μm; And / or, the inner diameter of the inner circular cylindrical ring is 5-30 mm, preferably 15-30 mm, such as 15 mm or 30 mm; And / or, the outer diameter of the inner circular cylindrical ring is 15-50 mm, preferably 30-50 mm, such as 30 mm or 50 mm; And / or, the inner diameter of the outer circular cylindrical ring is 15-50 mm, preferably 30-50 mm, such as 30 mm or 50 mm; And / or, the outer diameter of the outer circular cylindrical ring is 60-90 mm, such as 60 mm or 90 mm.

4. The filter element according to claim 2, characterized in that, The fibers of the inner circular cylindrical ring and the fibers of the outer circular cylindrical ring are combined by melt bonding and frictional force; And / or, the diameter of the fibers of the inner circular cylindrical ring is 3-10 μm, preferably 5-10 μm, such as 5 μm or 10 μm; And / or, the diameter of the fibers of the outer circular cylindrical ring is 8-15 μm, preferably 10-15 μm, such as 10 μm or 15 μm.

5. The filter element according to claim 1, wherein The isoelectric point of the fibers of the inner circular cylindrical ring is 4, and it is negatively charged in water with a pH of 7; And / or, the isoelectric point of the fibers of the outer circular cylindrical ring is 7-9, and it is positively charged in water with a pH of 7; And / or, the porosity at the position closest to the center of the circle in the inner circular cylindrical ring is 20-30%, such as 20% or 30%; And / or, the pore diameter at the position closest to the center of the circle in the inner circular cylindrical ring is 1-3 μm, such as 2 μm or 3 μm; And / or, the porosity at the position farthest from the center of the circle in the inner circular cylindrical ring is 40-70%, preferably 60%-70%, such as 60% or 70%; And / or, the pore diameter at the position farthest from the center of the circle in the inner circular cylindrical ring is 10-15 μm, preferably 13-15 μm, such as 13 μm or 15 μm; And / or, the porosity at the position closest to the center of the circle in the outer circular cylindrical ring is 40-60%, such as 50% or 60%; And / or, the pore diameter at the position closest to the center of the circle in the outer circular cylindrical ring is 5-10 μm, such as 7 μm or 10 μm; And / or, the porosity at the position farthest from the center of the circle in the outer circular cylindrical ring is 70-90%, such as 80% or 90%; And / or, the pore diameter at the position farthest from the center of the circle in the outer circular cylindrical ring is 15-20 μm, such as 17 μm or 20 μm.

6. The filter element according to claim 1, characterized in that, As the distance from the center of the circle decreases, the density of the fibers of the outer cylindrical ring and the inner cylindrical ring increases linearly; The density ρ of the fibers refers to the percentage of the fiber volume in the overall volume of the filter element. The porosity is denoted as δ. The distance from the fiber to the inner circle is defined as x, with the unit of mm. The thickness of the circular cylinder is b, with the unit of mm. The density of the fibers satisfies one or both of the following conditions: a. The density of the fibers is ρ = (1 - δ) × 100%. When x = 0, the distance from the fiber to the inner circle is defined as 0, which is the innermost side of the circular cylinder at this time. b. The change of the density of the fibers with the distance is ρ = ρ1 - ((ρ1 - ρ2) / b) × x.

7. The filter element according to claim 6, characterized in that, The density of the fibers satisfies one or several of the following conditions: a. When the outer diameter of the outer circular cylinder is 60 mm and the inner diameter is 30 mm, the fiber density near the center of the circle is 50%, and the fiber density far from the center of the circle is 20%. Starting from the position near the center of the circular cylinder, the fiber density at the distance from the starting point is ρ = (50 - x) × 100%. b. The fiber density near the center of the outer circular cylinder is 40% - 60%, such as 40% or 50%. c. The fiber density far from the center of the outer circular cylinder is 10% - 30%, such as 10% or 20%. d. The fiber density near the center of the inner circular cylinder is 70% - 80%, such as 70% or 80%. e. The fiber density far from the center of the inner circular cylinder is 30% - 60%, such as 30% or 40%.

8. A method for preparing a filter element, characterized in that, It includes the following steps: Prepare the inner circular cylinder and the outer circular cylinder with fibers by the melt - blowing process. The outer circular cylinder is wound around the outside of the inner circular cylinder type. The outer circular cylinder type consists of a core and a cortex. The core and the cortex are connected by an amide. The preparation steps of the cortex are as follows: S1: Treat the double - layer structure with the inner circular cylinder and the outer circular cylinder type by plasma. S2: Immerse the plasma - treated double - layer structure in a modified solution. The modified solution is an aqueous mixed solution of an adsorption material and a cross - linking material. The adsorption material is chitosan and / or polyethyleneimine. S3: Clean and dry the filter element obtained in step S2.

9. The preparation method according to claim 8, wherein The preparation steps satisfy one or several of the following conditions: a. The plasma treatment time is 10 - 120 s, preferably 60 - 120 s, such as 60 s or 120 s. b. The cross - linking material is glycidyl acrylate and / or glycerol glycidyl ether. c. The immersion time is 0.5 - 2 h, such as 1 h or 2 h, and the immersion temperature is 60 - 80 °C, such as 70 °C or 80 °C. d. The concentration of the adsorption material is 1 - 5%, preferably 3% - 5%, such as 3% or 5%. e. The concentration of the cross - linking material is 0.5 - 1%, such as 0.7% or 1%.

10. A filter element, characterized in that, It is prepared by using the preparation method of the filter element as described in claim 8 or 9.

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