An asymmetric gradient sintered composite dielectric, a preparation process and application thereof

Abstract

The application discloses an asymmetric gradient sintering composite medium and a preparation process and application thereof, and relates to the technical field of catalyst recovery and precious metal recovery. The composite medium comprises a support layer, a composite layer and a separation layer for intercepting various small substances; the separation layer comprises first particles for forming a porous structure; the support layer comprises second particles for forming a porous structure; the composite layer comprises the first particles and the second particles for forming a porous structure; the first particles and the second particles are both polyethylene substances; the thickness of the composite layer is not less than 0.1 microns; the crystallinity of the separation layer is 40%-85%; the PMI average pore diameter of the composite medium is 0.1-25 microns; and the overall porosity is 25%-75%. The composite medium has suitable pore diameters and porosities, and has a composite layer with a certain thickness, so that the composite medium has high interception efficiency and high flux, and has high composite strength, and the separation layer and the support layer are not easy to separate in a long time work; and the composite medium is particularly suitable for catalyst recovery and precious metal recovery.

Description

Technical Field

[0001] This invention relates to the field of porous sintered materials, and in particular to an asymmetric gradient sintered composite medium, its preparation process, and its applications. Background Technology

[0002] Sintering is an important material preparation process. Sintering refers to the process in which solid powder particles are physically shaped and then heated to a certain temperature to begin melting and bonding, finally forming a sintered porous material with a certain shape and properties.

[0003] For example, Chinese Patent CN103071400A discloses a method for producing a microporous membrane sintered filter element (applied by Ningbo Aiquou Water Purification Equipment Technology Co., Ltd.). This sintered filter element is made of ultra-high molecular weight polyethylene as the main raw material. It forms a microporous structure through physical thermal melting bonding. The average pore size of this sintered filter element is 0.28 μm, which has good retention efficiency and high retention accuracy for impurity particles. However, similarly, because the average pore size of the above-mentioned sintered filter element is relatively small, while the sintered filter element has high retention accuracy and high retention efficiency, its throughput is often relatively low. That is, the single-layer sintered filter element in the above-mentioned patent usually cannot achieve both high retention efficiency and high throughput, which limits the application range of the above-mentioned sintered material.

[0004] Furthermore, those skilled in the art will consider preparing sintered composite materials from single-layer sintered materials with high throughput through a composite process. Such composite materials typically include a separation layer and a support layer, where the separation layer ensures retention efficiency and the support layer increases throughput, thereby enabling the sintered composite material to simultaneously possess both high retention efficiency and high throughput. Generally, those skilled in the art at least hope that the types of sintering materials used to form each layer are the same (e.g., all organic materials, or even more specifically, all polyolefins), because if even the types of materials in each layer are different (e.g., one is an organic material and the other is an inorganic material), their compatibility will be very poor, and the sintering process will easily be affected by factors such as interfacial tension between different materials. The composite material exhibits extremely poor bonding strength, meaning the support layer and separator layer easily separate under relatively low pressure, hindering normal filtration, and particles in each layer are relatively easy to detach. Even if the sintering materials used to form the support and separator layers in the sintered composite material are of the same type (e.g., both are PE-based materials) and have a certain degree of compatibility, the bonding strength is still relatively poor. This still easily leads to the separation of the support and separator layers in the sintered composite material, and even the presence of "powder trapping" in some areas. The overall compressive strength and hardness of the sintered composite material are not high, resulting in a short service life. In particular, it cannot be used under high pressure and cannot be backwashed, which greatly limits the application range of sintered materials. Summary of the Invention

[0005] The objective of this invention is to provide an asymmetric gradient sintering composite medium, its preparation process, and its applications. This composite medium comprises a support layer, a composite layer, and a separation layer for retaining various fine substances. The composite medium as a whole has suitable pore size and porosity, and a composite layer of a certain thickness, thereby ensuring that the composite medium has high retention efficiency and high throughput while also possessing high composite strength (the separation layer and support layer are not easily separated). It is particularly suitable for catalyst recovery and the recovery of precious metals (such as platinum and iridium).

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An asymmetric gradient sintering composite medium includes a body having non-directional tortuous pathways within it. The body comprises a support layer, a composite layer, and a separation layer for trapping various fine substances. The composite layer is located between the support layer and the separation layer. The average pore size of the separation layer is smaller than that of the support layer.

[0008] The separation layer includes first particles for forming a porous structure; the support layer includes second particles for forming a porous structure; the composite layer includes first and second particles for forming a porous structure; both the first and second particles are polyethylene-based materials.

[0009] The thickness of the composite layer is not less than 0.1 μm, and the crystallinity of the separation layer is 40%-85%.

[0010] The composite medium has an average PMI pore size of 0.1-25 μm and an overall porosity of 25%-75%.

[0011] The composite medium of this invention can be mainly divided into three regions along its thickness: a support layer, a composite layer, and a separation layer. The support layer contains larger pores, primarily formed by the sintering of second particles. The separation layer contains smaller pores (the average pore size of the separation layer is smaller than that of the support layer), which can be used to trap various fine substances; it is formed by the sintering of first particles. The composite layer is located between the support layer and the separation layer, and both first and second particles coexist within it. The composite layer can be understood as being formed by the mutual permeation of the support layer and the separation layer. Therefore, the thickness of the composite layer is limited (not less than 0.1 μm). This directly reflects that the bonding depth between the support layer and the separation layer will not be too low, ensuring that there is a certain bonding strength between the support layer and the separation layer. Generally, the higher the penetration bonding depth between the support layer and the separation layer, that is, the thicker the composite layer, the higher the bonding strength and the less likely separation will occur (it can still be used normally under high pressure). At the same time, since both the first and second particles are made of polyethylene materials (with certain similar compatibility), it is easier to composite, ensuring the composite strength, which in turn makes the composite medium have a longer service life, meeting various applications, and making it less likely for the layers to separate during backwashing.

[0012] According to existing technology, the average pore size (PMI) can reflect the overall pore size within the composite medium to a certain extent; the larger the value, the larger the overall pore size of the composite medium. The value (mainly determined by the pore size within the separation layer) significantly affects the retention efficiency of the composite medium for various impurities. In this invention, the average PMI pore size of the composite medium is 0.1-25 μm (this composite medium is a microporous medium with relatively large pores), and its performance is fundamentally different from that of nanoscale porous materials. Through the synergistic effect of a certain average PMI pore size and non-directional tortuous pathways (the non-directional tortuous pathways refer to randomly oriented groove structures and / or discretely distributed pore structures, with each non-directional tortuous pathway interconnected), the composite medium of this invention ensures that it can effectively retain impurity particles of a certain size (mainly micron-sized impurities), achieving high retention efficiency.

[0013] Commonly used porosity testing methods include mercury intrusion porosimetry, density method, and gravimetric method; of course, those skilled in the art can also obtain the above parameters through other measurement methods, which are for reference only. Testing shows that the overall porosity of the composite medium of this invention is 25%-75%, indicating that the composite medium has a relatively large porosity and a large number of pores, which is beneficial for high throughput. Through the synergistic effect of the average pore size (PMI) and overall porosity of the composite medium, a high throughput and fast filtration speed are ensured, along with a high dirt-holding capacity, enabling the retention of more impurity particles and a long service life. Furthermore, with the appropriate crystallinity of the separation layer, the mechanical properties of the composite medium remain high.

[0014] Generally, those skilled in the art would consider higher crystallinity of the separator layer to be better. This is because higher crystallinity indicates more crystalline regions and a better degree of molecular orientation in the lattice, resulting in better mechanical strength and thus higher overall composite strength and compressive strength. However, in reality, higher crystallinity of the separator layer does not necessarily lead to higher mechanical strength of the composite medium or higher bonding strength between the separator and support layers. Rather, it is crucial to control the crystallinity of the separator layer within a suitable range. Excessive crystallinity can affect the interfacial tension between the separator and support layers, increasing it and hindering the bonding strength. Furthermore, excessively high crystallinity in the separator layer implies a higher degree of lattice orientation at the interface between the separator and support layers, which may make it more difficult for the support and separator layers to interpenetrate, further reducing the bonding force between them. Furthermore, the phenomenon of "powder trapping" may even occur. In this development, the DSC crystallinity of the separation layer is 40%-85%. This crystallinity is determined based on a certain pore size and porosity of this invention (the determination of crystallinity for nanoscale composite media is quite different from that of this invention). Under such crystallinity, on the one hand, the composite media can also have good mechanical strength, so that the stability of various properties of the composite media can be guaranteed when dealing with working conditions. At the same time, it was found that the synergistic effect of appropriate separation layer crystallinity and composite layer thickness results in more non-directionally arranged areas in the composite layer. These non-directionally arranged areas are more likely to permeate each other, promoting the bonding between the separation layer and the support layer. This reflects that the support layer and the separation layer have good bonding strength, which effectively solves the problem that conventional composite layer structures are prone to separation. The composite media of this invention is also not easy to separate under backwashing, and there is no phenomenon of easy particle detachment.

[0015] This invention employs a structure consisting of a support layer, a separation layer, and a composite layer. By ensuring the average pore size and porosity of the composite medium are within a suitable range, and the crystallinity of the separation layer is also within a suitable range, the pore structure of the separation layer and the composite layer exhibits good stability under pressure. This prevents pore collapse during fluid filtration, ensuring high flux and excellent retention efficiency in the composite medium. It also helps maintain the bonding strength of the composite layer, preventing separation between the support layer and the separation layer. Furthermore, the entire composite medium possesses high mechanical strength (high pressure resistance and hardness). Under the combined influence of the average pore size and porosity of the composite medium, the crystallinity of the separation layer, and the thickness of the composite layer, an unexpected technical effect has been discovered: slow flux decay and low clogging (high dirt-holding capacity). This is likely because the pore size of the composite medium does not change too rapidly with thickness, exhibiting a suitable gradient.

[0016] In this invention, the average pore size of the composite medium is obtained by testing with a PMI pore size analyzer; the DSC crystallinity of the composite medium can be obtained by differential scanning calorimetry.

[0017] As a further improvement of the present invention, the average SEM particle size of the first particle is 5-60 μm, and the average SEM particle size of the second particle is 80-500 μm.

[0018] In powder sintering, the pore size of the sintering medium is closely related to the particle size of the powder. Generally, smaller powder particles are more likely to form smaller pores under certain sintering conditions. Since the separation layer is mainly used to trap various tiny impurity particles, its internal pore size is relatively small. Therefore, the particle size of the first particle (several first particles sintered to form the separation layer) should not be too large. After sintering, the SEM average particle size of the first particle should be controlled at 5-60 μm. Under this particle size, the separation layer can be effectively separated. Having a suitable pore size ensures retention efficiency; on the other hand, combined with the appropriate DSC crystallinity of the separation layer, it ensures that the number of pores in the separation layer is not too small, so as not to affect the flux of the composite medium, and at the same time, it is beneficial to have a higher impurity recovery rate during the subsequent backwashing process; at the same time, the particle size of the first particle is not too small, because research has found that if the particle size of the first particle is too small after sintering, the bonding between the first particles may not be strong enough, and they are prone to falling off during long-term filtration, especially during backwashing, which not only affects the purity of the fluid, but also greatly shortens the service life of the composite medium.

[0019] Since the support layer has a macroporous structure, the particle size of the second particles (sintered from several second particles to form the support layer) needs to be relatively large. After sintering, the average SEM particle size of the second particles should be controlled between 80-500 μm. With this particle size, on the one hand, it can ensure that there are large-diameter pores in the support, resulting in a large number of pores and a high porosity of the support layer and even the composite medium. On the other hand, the second particles can be considered as the "skeleton" that constitutes the internal structure of the support layer. If the particle size is too small, it will greatly affect the stability of the pores in the support layer. During high-pressure filtration, the pores in the support are prone to collapse and deformation, making the entire composite medium unusable. When the sintered second particles have a suitable particle size, it can ensure the compressive strength of the support layer, thereby ensuring that the entire composite medium has high mechanical strength.

[0020] After sintering, the combined action of the first and second particles of a certain size further enhances the composite medium's good throughput and high retention efficiency, while also exhibiting high compressive strength and hardness.

[0021] In this invention, the average particle size of the first and second particles under SEM can be obtained by characterizing the cross-section of the sintered porous medium using a scanning electron microscope, followed by measurement using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement, and then performing corresponding calculations. In actual measurement, the cross-section (thickness direction) of the sintered porous medium can be characterized first using an electron microscope to obtain the corresponding SEM image. Since the distribution of the first and second particles in the sintered porous medium on the cross-section is approximately uniform, a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 100μm 2 (10μm x 10μm) or, the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to determine the SEM average particle size of the first and second particles on that area. Perform several tests (preferably more than 10 times, the specific number depends on the situation), and take the average value to obtain the SEM average particle size of the first and second particles. Of course, those skilled in the art can also obtain the above parameters through other measurement methods. The above measurement methods are for reference only.

[0022] As a further improvement of the present invention, the thickness of the composite layer is 1-1000 μm, preferably 10-800 μm; more preferably 50-500 μm.

[0023] Within the composite layer, a connection node is formed between the first particle and the second particle, and the SEM average width of the connection node is 3-50 μm.

[0024] The composite layer can be understood as a support layer and a separation layer that permeate each other. Within the composite layer, both the first and second particles coexist (and if a third particle exists within the support layer, it will also exist within the composite layer). The thickness of the composite layer significantly affects the bonding strength between the separation and support layers, thus influencing the various mechanical properties of the composite medium. If the composite layer thickness is too small, the support and separation layers may separate under pressure, affecting filtration efficiency, especially during backwashing. Furthermore, due to the relatively small thickness of the separation layer, it is easier for the separation layer to separate from the support layer or for some particles to detach. By selecting an appropriate composite layer thickness, and with the combined action of the first and second particles of suitable size, a tight bond between the support and separation layers is ensured, enabling long-term high-efficiency filtration. Simultaneously, the composite layer should not be too thick, ensuring that the composite medium as a whole has good porosity, thus achieving good flux.

[0025] Meanwhile, within the composite layer, there are strip-like structures such as filamentous connecting ribs or overlapping nodes between some adjacent first and second particles. These are called connecting nodes. The connecting nodes are used to further connect the first and second particles, thereby affecting the bonding strength between the separation layer and the support layer. Connecting nodes of a certain thickness are beneficial to further improve the composite strength of the composite medium, while the first and second particles are less likely to fall off under high pressure. Combined with the optimal selection of the composite layer thickness, this further ensures that the composite medium has high composite strength, high compressive strength, and high hardness.

[0026] In this invention, the SEM average width and other features of the connecting nodes can be obtained by characterizing the cross-section of the composite medium using a scanning electron microscope, then selecting a certain area and measuring it using computer software (such as Matlab, NIS-Elements, etc.) or manually, taking the average value, and then further calculating the corresponding SEM average width. Of course, it is understood that those skilled in the art can also obtain the above parameters through other measurement methods.

[0027] As a further improvement of the present invention, the ratio of the average SEM particle size of the second particle to the average SEM particle size of the first particle is 5-30; the ratio of the average SEM width of the connecting node to the average SEM particle size of the first particle is 1:1.1-4.

[0028] Research has shown that when the ratio of the SEM average particle size of the second particle to that of the first particle is too small, either the overall flux of the composite medium will be too low (both the particle sizes of the first and second particles are too small), or the retention efficiency will be too low (both the particle sizes of the first and second particles are too large). Conversely, when the ratio of the SEM average particle size of the second particle to that of the first particle is too large, the overall pressure resistance and hardness of the composite medium will be too low. Especially when backwashing is required, the layers are easily separated, and the particles are easily detached. By controlling the ratio of the SEM average particle size of the second particle to that of the first particle within a suitable range, it is more beneficial to obtain a composite medium with high flux and high retention efficiency.

[0029] Furthermore, the present invention further adjusts the SEM average width of the connecting node to the SEM average particle size of the first particle, thereby further ensuring that the first particle and the second particle are tightly bonded and the particles are not easily separated. Therefore, the layers are not easily separated under greater pressure, and the particles are not easily detached, resulting in a composite bond with higher bonding strength, higher pressure resistance and hardness, and the ability to retain and backwash for a long time, resulting in a long service life.

[0030] As a further improvement of the present invention, the thickness of the separation layer is 0.1-5 mm, and the ratio of the thickness of the separation layer to the thickness of the composite medium is 1%-20%.

[0031] The separation layer is the area used to trap various fine impurities, and its thickness has a certain impact on the impurity trapping efficiency. In the prior art, it is generally desirable for the separation layer to be thicker, because if its thickness is too small, the trapping efficiency of the composite medium will be too low. However, in this invention, it is not desirable for the separation layer to be too thick, because if its thickness is too large, it will affect the overall throughput of the composite medium. On the other hand, when the composite medium needs backwashing, if the separation layer is too thick, it will be difficult for impurities to be washed out through the backwashing process, and the impurity recovery rate will be too low.

[0032] The separation layer of this invention has a suitable thickness. On the one hand, in conjunction with the tortuous passage, it further ensures the interception efficiency, thereby enabling the separation layer to fully and efficiently capture various impurities. On the other hand, during backwashing, because the separation layer thickness is not too thick, various impurities in the separation layer can be washed out, resulting in a high impurity recovery rate. In addition, by controlling the ratio of the separation layer thickness to the composite medium thickness, and combining it with a certain PMI average pore size and porosity of the composite medium, it is ensured that the composite medium still has a high throughput, high pressure resistance, and high hardness, meeting the needs of practical applications.

[0033] In this invention, the thickness of the separation layer can be obtained by characterizing the cross-section of the composite medium using a scanning electron microscope, then selecting a certain area and measuring it using computer software (such as Matlab, NIS-Elements, etc.) or manually, taking the average value, and then further calculating the corresponding thickness value; of course, it is understood that those skilled in the art can also obtain the above parameters through other measurement methods.

[0034] As a further improvement of the present invention, the distribution density of the second particle is 1-30 particles / mm. 2 The composite medium has a basis weight of 0.5-1.2 g / cm³. 2 .

[0035] The second particle can be considered as the "skeleton" constituting the internal structure of the support layer. Its particle size ensures the stability of the pores within the support layer, thereby facilitating the production of composite media with high mechanical strength. However, in addition to the particle size, research has found that the number (i.e., distribution density) of the second particles also affects the stability of the pores within the support layer to some extent. By controlling the number of second particles within the support layer, and through their synergistic effect with second particles of appropriate size, the support layer can achieve sufficient porosity and strength. The second particles are tightly bonded to each other, and the pores remain stable during long-term retention filtration and backwashing. Especially when a third particle is present within the support layer, and the porosity is high, it is even more necessary to control the number of second particles and ensure that their distribution density is within a suitable range.

[0036] Basis weight can also be considered as areal density. A suitable basis weight ensures that the composite medium has appropriate porosity, high flux, good mechanical strength, high hardness, and is not too soft.

[0037] In this invention, the distribution density of the second particle can be determined by characterizing the morphology of the composite medium cross-section using a scanning electron microscope, and then selecting a certain area (e.g., 1 μm). 2 (1μm x 1μm) or 100μm 2 (10μm x 10μm) or, the specific area size depends on the actual situation. Then, after measuring using computer software (such as Matlab, NIS-Elements, etc.) or manually, obtain the number of second particles on that area, and calculate the distribution density value. Perform several tests (preferably more than 10 times), take the average value, and thus obtain the distribution density of the second particles.

[0038] As a further improvement of the present invention, the support layer further includes a third particle, which is a polyethylene material, and the SEM average particle size of the third particle is 8-80 μm.

[0039] In some fields, we aim to maximize the throughput (permeability) of composite media, i.e., to achieve a high porosity (especially in the support layer). This invention aims to increase the porosity of the support layer and the overall composite media by adding suitable third particles. Research has shown that the third particle should be made of polyethylene, exhibiting good compatibility with the second particles, allowing for easy and uniform mixing without "powder trapping," and without affecting the hardness and compressive strength of the composite media. Furthermore, by controlling the SEM average particle size of the third particle to 8-80 μm, this particle size facilitates its proximity to and adhesion to the second particles, contributing to the formation of more pores within the support layer. This results in higher porosity in the support layer and a higher throughput for the composite media, while maintaining minimal impact on the mechanical properties of the composite media, ensuring its high compressive strength.

[0040] As a further improvement of the present invention, the ratio of the SEM average particle size of the second particle to the SEM average particle size of the third particle is 5-35:1; and the SEM average particle size of the third particle is greater than the SEM average particle size of the first particle.

[0041] Research has shown that when the ratio of the particle size of the second particle to that of the third particle is controlled within a suitable range, the third particle will more easily approach and adhere to the second particle, thereby forming more pores and further increasing the flux of the composite medium. In addition, it should be noted that the particle size of the third particle should not be too small, especially not smaller than the particle size of the first particle. If the particle size of the third particle is too small, it may affect the porosity and strength of the support layer, thereby affecting the flux and pressure resistance of the composite medium.

[0042] As a further improvement of the present invention, the surface of the separation layer away from the support layer is a first surface, and the surface of the support layer away from the separation layer is a second surface, wherein the pore area ratio of the second surface is 10%-70%.

[0043] The ratio of the pore area ratio of the first surface to the pore area ratio of the second surface is 0.3-0.9:1.

[0044] In impurity filtration, the second surface is typically used as the inlet surface and the first surface as the outlet surface. Since the second surface is the first area in the composite medium to come into contact with the fluid, a relatively large pore area ratio is desirable to facilitate rapid fluid flow. However, an excessively large pore area ratio would weaken the compressive strength of the composite medium and cause particulate matter to detach, negatively impacting fluid purity. Research has shown that a pore area ratio of 10%-70% on the second surface is optimal, facilitating rapid fluid flow while also ensuring adequate pore volume. The second surface exhibits good resistance strength and can withstand pressure for extended periods. The first surface, being part of the separation layer, has a relatively smaller pore area ratio to ensure retention efficiency (reflecting a relatively dense separation layer). However, the pore area ratio of the first surface cannot be too low, as backwashing is required in some applications, and a low pore area ratio would affect impurity recovery. Research has shown that the ratio of the pore area ratio of the first to the second surface should be controlled at 0.3-0.9:1, ensuring both retention efficiency and facilitating backwashing, thus achieving a higher impurity recovery rate. The synergistic effect between the pore area ratios of the first and second outer surfaces further enhances the composite medium's flow velocity, allowing for rapid fluid passage, shortening filtration time, and providing greater pressure resistance to meet practical application requirements.

[0045] In this invention, the porosity of the first and second surfaces can be determined by scanning electron microscopy to characterize the morphology of the porous medium surface, and by selecting a certain area, for example, 1 μm. 2 (1μm x 1μm) or 100μm 2 (10μm x 10μm) or, the specific area size depends on the actual situation. Then, use the corresponding computer software or manually to measure the total area of ​​the holes on that area, calculate the hole area ratio, conduct several tests (at least 10 times), and take the average value.

[0046] As a further improvement of the present invention, the first surface has a plurality of mold wall contact areas, the SEM average width of the mold wall contact areas is 5-35 μm; the area ratio of the mold wall contact areas is 10%-65%.

[0047] The area ratio of the mold wall contact area is equal to the SEM area of ​​the mold wall contact area / the SEM area of ​​the first surface.

[0048] In this invention, the mold wall contact area on the first surface is formed by the second particle contacting the inner wall of the mold during sintering and through the molten state during sintering (the mold wall contact area is equivalent to a part of the solid part of the surface, a smooth and flat surface formed by the direct contact between the particle and the mold). The SEM average width of the mold wall contact area reflects, to some extent, the size of the skeleton material on the surface of the sintered porous material, thereby affecting the compressive strength of the composite medium surface. By controlling the SEM average width of the mold wall contact area within the range of 5-35 μm, the composite medium has a good skeleton foundation, which is beneficial for the second surface of the composite medium to have good compressive strength, especially for backwashing. The area ratio of the mold wall contact area represents the solid part of the contact between the second particle and the mold in the sintered composite medium, so the area ratio of the mold wall contact area also affects the compressive strength of the composite medium surface during application to some extent. By controlling the area ratio of the mold wall contact area within the range of 10%-65%, this invention further enables the sintered composite medium to have good compressive strength, and further improves the surface compressive strength of the composite medium under conditions such as backwashing.

[0049] As a further improvement of the present invention, the thickness of the composite medium is 10-50 mm; the retention efficiency of the composite medium for impurity particles with a particle size of 1-20 micrometers is not less than 80%.

[0050] The flux of the composite medium is 200-2000 L / min @ 7 kPa;

[0051] The Shore A hardness of the composite medium is not less than 70HA;

[0052] The pressure resistance of the composite medium is not less than 300N.

[0053] The thickness of the composite medium can be determined by characterizing its structure using a scanning electron microscope, followed by calculation using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement (other testing instruments can also be used). When the thickness of the composite medium is too small, its mechanical strength will be low; at the same time, due to the short filtration time, effective filtration will not be possible. When the thickness of the composite medium is too large, its filtration time will be too long, resulting in excessive time costs; and it will also affect the overall throughput. The composite medium of this invention has a thickness of 10-50 mm, which, together with the ideal pore structure, ensures that the composite medium not only has high mechanical strength but also can effectively filter and has high retention efficiency.

[0054] The retention and flow rate tests demonstrate that the composite medium of the present invention not only has high efficiency in retaining various fine impurities, but also has good flow rate. The hardness and pressure resistance tests demonstrate that the composite medium of the present invention has good hardness and pressure resistance, making it suitable for various processing methods and enabling long-term filtration, retention, and backwashing, thereby obtaining more of those expensive impurities (such as precious metal catalysts).

[0055] The Shore A hardness of the composite medium can be tested using a Shore A hardness tester. The Shore A hardness of the composite medium is obtained by taking the average value after three tests.

[0056] The air flux of the composite medium can be tested using the following method: An air permeability tester is used to test the air flux of the composite medium. The air pressure is adjusted to the test pressure, which is 7 kPa. The data is read and recorded to obtain the air flux of the composite medium. The air permeability area of ​​the composite medium is controlled at 250 cm². 2 Under the conditions;

[0057] Test method for compressive strength: Cut a 1cm wide and 3cm long arched sample of the composite medium and place it on a servo tensile testing machine (model: HD-A513-C) to test the compressive strength.

[0058] Furthermore, the present invention also provides a preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0059] S1, equipped with material A and material B; material A contains a first particle with a weight-average molecular weight of 3 million to 8 million, the first particle is UPE, and the particle size of the first particle is less than 100 μm;

[0060] Material B contains a second particle with a weight-average molecular weight of 200,000 to 800,000, the second particle is HDPE, and the particle size of the second particle is greater than 200 μm.

[0061] S2, one-time sintering: first, material B is evenly loaded into the sintering mold and compacted, then the temperature is raised to 150-180℃ at a rate of 3-10℃ / min, then held for 80-120min, and then cooled to 20-40℃.

[0062] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 110-140℃, and then hold it for 20-50 minutes;

[0063] S4 involves secondary sintering, followed by heating to 150-180℃, with a holding time of 70%-95% of that in S2.

[0064] S5, natural cooling, yields an asymmetric composite medium.

[0065] As a further improvement of the present invention, material B further comprises a third particle with a weight-average molecular weight of 2 million to 6 million, the third particle being UPE with a bulk density of 0.15-0.25 g / cm³. 3 The mass fraction of the third particle in material B is 10%-40%.

[0066] As a further improvement of the present invention, in the first sintering of S2, the temperature is first raised to 110-140°C, and the holding time is 2-5 times that of the holding time in S3, and then the temperature is raised to 150-180°C.

[0067] As a further improvement of the present invention, the mass ratio of material A to material B in S1 is 1:3-8; the heating rate in S3 is 3-10℃ / min; and the heating rate in S4 is 60%-90% of the heating rate during the first sintering in S2.

[0068] In preparing the asymmetric gradient sintering composite medium of the present invention, materials A and B are first prepared, wherein material A is used to form a separation layer and material B is used to form a support layer. Since the pore size within the separation layer is relatively small, material A contains first particles, which are UPE particles with a weight-average molecular weight of 3-8 million and a relatively small particle size (generally, raw materials with smaller particle sizes are easier to sinter into smaller pores), not exceeding 100 μm. Subsequently, by combining this with appropriate sintering processes, it is beneficial to obtain a separation layer with ideal pore size (smaller pore size in the separation layer), facilitating efficient retention of various... Impurities are eliminated, and the number of pores within the separation layer is not too small, so as not to affect the overall throughput of the composite medium. Because the pore size within the separation layer is relatively large, material B contains a second particle, HDPE (high-density polyethylene), with a weight-average molecular weight of 200,000-800,000 and a relatively large particle size (greater than 200 μm). Subsequent sintering processes facilitate the formation of an ideal support layer. The support layer has large pore sizes and a large number of pores, which contributes to a high porosity in the composite medium and a high overall throughput. Preferably, the bulk density of HDPE is not less than 0.4 g / cm³. 3 The high density helps ensure that the support layer, despite its large internal pores, still has good mechanical strength, and the overall hardness and compressive strength of the medium are both high.

[0069] Furthermore, research has found that, based on the selection of materials A and B, the optimal mass ratio of material A to material B is 1:3-8 (too much material A will result in low porosity and low air permeability of the entire composite medium; too little material A will result in low retention efficiency or poor mechanical properties). Combined with appropriate sintering processes, an ideal composite medium structure can be obtained, resulting in high air permeability and high retention efficiency, while also ensuring the composite strength between layers. In some fields, we aim to maximize the flux (air permeability) of the composite medium, i.e., to achieve a high porosity (especially in the support layer). Research has shown that adding a small amount of a third particle (10%-40% by mass, with the remainder being second particles) to material B, where the third particle is UPE with a weight-average molecular weight of 2-6 million and a bulk density of 0.15-0.25 g / cm³, can significantly improve the composite medium's structure. 3 By adding UPE with a relatively low bulk density to material B, and with the synergistic effect of a certain sintering process, the third UPE particles will mix with the second HDPE particles and bond and melt together, thereby forming more pores and further increasing the number of pores in the support layer, thus improving the porosity of the support layer and even the entire composite medium. At the same time, the third particles are relatively few (and will not sinter pores with excessively large diameters), so they have little impact on the mechanical strength of the support layer and even the entire composite medium.

[0070] Meanwhile, since both material A and material B are polyethylene-based substances, they have good compatibility and, with the synergistic effect of a certain sintering process, can easily form a composite layer of a certain thickness, thereby ensuring the composite strength of the composite medium (the layers are not easily separated), and making the composite medium have high hardness and high compressive strength.

[0071] As a preferred option, after materials A and B are prepared, they can be dried at a temperature of 50-80℃ for 40-80 minutes. Drying helps to remove moisture from materials A and B. If the moisture content in the materials is too high, the materials may agglomerate, which will affect sintering and make it difficult to form a composite medium with ideal pore size and porosity.

[0072] After preparing materials A and B, the sintering process begins. Due to the need to prepare an asymmetric composite gradient medium, a two-stage sintering method is used in this invention. First, the support layer is prepared. During support layer preparation, material B is uniformly loaded into the sintering mold and compacted. Then, the temperature is raised at a rate of 3-10℃ / min. Since material B mainly consists of large-diameter HDPE particles, this heating rate ensures a rapid increase in temperature (without excessive shrinkage of the particles) and guarantees uniform heating of most particles, minimizing temperature differences between particles, thus facilitating subsequent sintering. The material is then held at 150-180℃ for 80-120 minutes. This sintering temperature and holding time... Under the combined action of the two processes, the particles in material B will melt together, and adjacent particles will begin to bond together, forming the initial support layer. The support layer will be fully formed only after the second sintering. (After the first sintering, some particles will melt and bond together, forming pores of a certain size; at the same time, some particles will not yet bond together or will only be initially bonded together.) Therefore, it is important to note that the support layer should not be fully sintered during the first sintering. If it is fully sintered at this time, the second particles in material B will be further sintered during the second sintering. At the same time, since HDPE has a small molecular weight, a relatively high melt index, and good fluidity, it is easy to have an "over-sintering" phenomenon, which will greatly reduce the number of pores in the support layer, and ultimately result in low porosity and air permeability (flux) of the composite medium.

[0073] Preferably, during the first sintering, the temperature should not be directly raised to 150-180℃ (above the melting point). Instead, the temperature should be raised to 110-140℃ (near the melting point, even if melting and adhesion occur between particles, it is minimal, thus preventing over-sintering; this temperature is also not significantly different from the final sintering temperature of 150-180℃) and held for a period of time. The purpose of this is to ensure that the temperature between particles is almost uniform, which facilitates subsequent sintering and produces pores of the ideal size and number. This treatment is especially necessary when material B contains both second and third particles, because the internal heating rates of the second and third particles will inevitably differ under the same heating conditions (HDPE and UPE still exhibit certain differences). The difference lies in the heating effect on the particles in different areas of the mold. If the temperature is directly raised to 150-180℃, there will inevitably be a certain temperature difference between some of the second and third particles. If this temperature difference is too large, it will be detrimental to subsequent sintering. By first holding the temperature at 110-140℃, the temperature between the second and third particles can be greatly reduced, and the temperature between the particles is almost the same, which is conducive to subsequent sintering and ensures the various properties of the product. At the same time, since the mass of material B is relatively large, the holding time at 110-140℃ also needs to be relatively long, which is 2-5 times the holding time in S3, preferably 100-150 minutes. This can further ensure that the temperature of the particles in material B is basically the same.

[0074] After the support layer is initially sintered and formed, it is cooled to 20-40℃. Then, material A, which is used to form the separation layer, is uniformly loaded into the sintering mold and compacted. The temperature is then raised to 110-140℃ and held for 20-50 minutes for pretreatment. The purpose of this pretreatment is to ensure that the temperature of the particles in the support layer is basically the same as the temperature of material A, and that the temperature between the particles in material A is also basically the same. This is beneficial for subsequent sintering, thereby ensuring the formation of a composite layer of a certain thickness, and thus ensuring the composite strength and compressive strength of the composite medium. Since the mass of material A is relatively small, the holding time is short, only 20-50 minutes is needed (too long a holding time can easily affect the pore size and porosity of the support layer). Preferably, the heating rate of S3 pretreatment is 3-10℃ / min. This heating rate ensures efficiency and prevents the temperature difference between the first particles of material A from being too large. After the pretreatment, the temperature between the particles can be almost the same.

[0075] After pretreatment, a second sintering is performed, with the sintering temperature still controlled at 150-180℃. At this temperature, the surfaces of the already bonded particles further fuse together due to the movement and diffusion of molecular chain segments, resulting in a stable and firm bond. By controlling the sintering temperature and holding time, the particles can bond while retaining some pores between them, ultimately forming an ideal porous material. In this invention, the holding time during the preparation of the separation layer is crucial. Firstly, to ensure a high flux of the entire composite medium, the separation layer must not be very thick, so the holding time should not be too long. Research shows that the holding time should not exceed the holding time of the first sintering, otherwise over-sintering will occur (both the separation layer and the support layer will be over-sintered), resulting in low porosity, low flux, and low strength of the entire composite medium. Conversely, if the holding time is too short, insufficient sintering will occur, leading to excessively high crystallinity of the separation layer and the presence of "powder inclusions" in the entire composite medium. The separation layer and the support layer will not bond well, resulting in an overall poor composite medium. The composite strength and compressive strength of the first sintering were too low. Research showed that the holding time for the second sintering was 70%-95% of the holding time in S2 (the first sintering time, i.e., the time spent holding at the highest temperature after the first sintering). This holding time, combined with the corresponding sintering temperature, ensures thorough sintering and perfect bonding within the separation layer and support layer, resulting in an ideal porous structure, high throughput and retention efficiency, and a composite layer of sufficient thickness. The composite medium also exhibits good composite strength and compressive strength. Preferably, the heating rate in S4 is 60%-90% of the heating rate during the first sintering in S2. This further ensures that the temperature difference between the particles in the support layer and material A is very small, and the temperature difference between the first particles in material A is also small. This results in relatively uniform pore size within the separation layer, ensuring retention efficiency, and also guarantees bonding strength, forming a composite layer of sufficient thickness. The entire composite medium exhibits high composite strength, meeting the requirements of practical applications.

[0076] After secondary sintering, the material is naturally cooled to obtain an asymmetric composite medium. This composite medium includes a support layer, a composite layer, and a separation layer for retaining various fine substances. The composite medium as a whole has a suitable pore size and porosity, and the layers are tightly bonded together, thus ensuring that the composite medium has high retention efficiency and high throughput, as well as high composite strength (the separation layer and the support layer are not easily separated), and high hardness and compressive strength. It is particularly suitable for the recovery of catalysts and precious metals (such as platinum and iridium).

[0077] Furthermore, the present invention also provides an application of an asymmetric gradient sintering composite medium, wherein the composite medium is used for catalyst recovery and precious metal recovery.

[0078] As is well known, conventional phase transformation membranes are insufficient in hardness and pressure resistance, thus failing to meet the requirements of backwashing (backwashing requires the product to have a certain pressure resistance to withstand the gas pressure during backwashing). However, the composite medium prepared in this invention has high hardness and pressure resistance, and is mainly used in the fields of interception filtration and material recovery, especially the recovery of catalysts (especially some expensive metal catalysts) and precious metals such as platinum, iridium and palladium. The corresponding substances are first intercepted, and then recovered by reverse gas filling.

[0079] The beneficial effects of this invention are as follows: The asymmetric gradient sintering composite medium provided by this invention includes a support layer, a composite layer, and a separation layer for retaining various fine substances. This composite medium has suitable average pore size and porosity, thus ensuring high retention efficiency and high throughput. Simultaneously, the suitable thickness of the composite layer and the certain crystallinity of the separation layer ensure a tight bond between the layers, resulting in high composite strength and high pressure resistance, enabling long-term retention and filtration under high pressure. Furthermore, since the separation layer includes first particles for forming a porous structure, and the support layer includes second particles for forming a porous structure, by controlling the particle size of the first and second particles, as well as the thickness of the separation layer, this composite medium is suitable for backwashing and can achieve good recovery of retained impurities. Therefore, it is particularly suitable for the recovery of expensive catalysts and precious metals (such as platinum and iridium). The preparation method provided by this invention can conveniently, quickly, and effectively prepare the aforementioned asymmetric gradient sintering composite medium. Attached Figure Description

[0080] The present invention will be further described below with reference to the accompanying drawings:

[0081] Figure 1 This is a scanning electron microscope (SEM) image of the composite layer region on the cross-section of the sintered composite medium prepared in Example 1, with a magnification of 200×; the red boxes represent the connection nodes.

[0082] Figure 2 This is a scanning electron microscope (SEM) schematic diagram of the support layer region on the cross-section of the sintered composite medium prepared in Example 1, where the magnification is 100×.

[0083] Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the first surface of the sintered composite medium prepared in Example 6, with a magnification of 200×; the red circle represents the mold wall contact area.

[0084] Figure 4 This is a scanning electron microscope (SEM) schematic diagram of the second surface of the sintered composite medium prepared in Example 6, where the magnification is 50×.

[0085] Figure 5This is a scanning electron microscope (SEM) schematic diagram of the separation layer region on the cross-section of the sintered composite medium prepared in Example 6, with a magnification of 200×.

[0086] Figure 6 This is a scanning electron microscope (SEM) schematic diagram of the composite layer region on the cross-section of the sintered composite medium prepared in Example 6, where the magnification is 50×.

[0087] Figure 7 This is a scanning electron microscope (SEM) schematic diagram of the separation layer region on the cross-section of the sintered composite medium prepared in Example 2, where the magnification is 100×.

[0088] Figure 8 This is a scanning electron microscope (SEM) schematic diagram of the composite layer region on the cross section of the sintered composite medium prepared in Example 2, where the magnification is 100×.

[0089] Figure 9 This is a scanning electron microscope (SEM) schematic diagram of the support layer region on the cross-section of the sintered composite medium prepared in Example 2, where the magnification is 50×.

[0090] Figure 10 This is a scanning electron microscope (SEM) schematic diagram of the separation layer region on the cross-section of the sintered composite medium prepared in Example 7, where the magnification is 50×.

[0091] Figure 11 This is a scanning electron microscope (SEM) schematic diagram of the composite layer region on the cross section of the sintered composite medium prepared in Example 7, where the magnification is 100×.

[0092] Figure 12 This is a scanning electron microscope (SEM) schematic diagram of the support layer region on the cross-section of the sintered composite medium prepared in Example 7, with a magnification of 50×. Detailed Implementation

[0093] The present invention will be further described in detail below with reference to the embodiments. Unless otherwise specified, the raw materials and equipment used to prepare the sintering composite medium in the following embodiments can be purchased commercially.

[0094] Example 1: A process for preparing an asymmetric gradient sintering composite medium, comprising the following steps:

[0095] S1, equipped with material A and material B; wherein material A contains a first particle with a weight average molecular weight of 4.2 million, the first particle is UPE, and the particle size of the first particle is less than 100μm; wherein material B contains a second particle with a weight average molecular weight of 450,000, the second particle is HDPE, and the particle size of the second particle is greater than 200μm.

[0096] The mass ratio of material A to material B is 1:7;

[0097] S2, one-time sintering: First, material B is evenly loaded into the sintering mold and compacted. The temperature is first raised to 125℃ and held for 120 minutes at a rate of 5℃ / min. Then, the temperature is raised to 160℃ at a rate of 5℃ / min. After holding for 100 minutes, the temperature is cooled to 30℃.

[0098] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 30min.

[0099] S4, secondary sintering, followed by heating to 175℃ at a rate of 4℃ / min, and holding for 90min;

[0100] S5, natural cooling, yields an asymmetric composite medium.

[0101] Example 2: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0102] S1, equipped with material A and material B; wherein material A contains a first particle with a weight average molecular weight of 4.5 million, the first particle is UPE, and the particle size of the first particle is less than 100μm; wherein material B contains a second particle with a weight average molecular weight of 500,000, the second particle is HDPE, and the particle size of the second particle is greater than 200μm.

[0103] The mass ratio of material A to material B is 1:6;

[0104] S2, one-time sintering: First, material B is evenly loaded into the sintering mold and compacted. The temperature is first raised to 120℃ and held for 110 minutes at a rate of 6℃ / min. Then, the temperature is raised to 160℃ at a rate of 6℃ / min. After holding for 95 minutes, the temperature is cooled to 30℃.

[0105] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 30min.

[0106] S4, secondary sintering, followed by heating to 175℃ at a rate of 4℃ / min, and holding for 85min;

[0107] S5, natural cooling, yields an asymmetric composite medium.

[0108] Example 3: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0109] S1, equipped with material A and material B; wherein material A contains a first particle with a weight average molecular weight of 5 million, the first particle is UPE, and the particle size of the first particle is less than 100μm; wherein material B contains a second particle with a weight average molecular weight of 550,000, the second particle is HDPE, and the particle size of the second particle is greater than 200μm.

[0110] The mass ratio of material A to material B is 1:5;

[0111] S2, one-time sintering: First, material B is evenly loaded into the sintering mold and compacted. The temperature is first raised to 120℃ and held for 105 minutes at a rate of 8℃ / min. Then, the temperature is raised to 170℃ at a rate of 8℃ / min. After holding for 90 minutes, the temperature is cooled to 30℃.

[0112] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 40min.

[0113] S4, secondary sintering, followed by heating to 175℃ at a rate of 6℃ / min, and holding for 82min;

[0114] S5, natural cooling, yields an asymmetric composite medium.

[0115] Example 4: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0116] S1, equipped with material A and material B; wherein material A contains a first particle with a weight average molecular weight of 6 million, the first particle is UPE, and the particle size of the first particle is less than 100μm; wherein material B contains a second particle with a weight average molecular weight of 650,000, the second particle is HDPE, and the particle size of the second particle is greater than 200μm.

[0117] The mass ratio of material A to material B is 1:4;

[0118] S2, one-time sintering: First, material B is evenly loaded into the sintering mold and compacted. The temperature is first raised to 115℃ and held for 95 minutes at a rate of 6℃ / min. Then, the temperature is raised to 170℃ at a rate of 6℃ / min. After holding for 100 minutes, the temperature is cooled to 40℃.

[0119] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 30min.

[0120] S4, secondary sintering, followed by heating to 175℃ at a rate of 4℃ / min, and holding for 80min;

[0121] S5, natural cooling, yields an asymmetric composite medium.

[0122] Example 5: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0123] S1, equipped with material A and material B; wherein material A contains a first particle with a weight average molecular weight of 7 million, the first particle is UPE, and the particle size of the first particle is less than 100μm; wherein material B contains a second particle with a weight average molecular weight of 800,000, the second particle is HDPE, and the particle size of the second particle is greater than 200μm.

[0124] The mass ratio of material A to material B is 1:3;

[0125] S2, one-time sintering: First, material B is evenly loaded into the sintering mold and compacted. The temperature is first raised to 115℃ and held for 90 minutes at a rate of 6℃ / min. Then, the temperature is raised to 160℃ at a rate of 6℃ / min and held for 95 minutes. Finally, the temperature is cooled to 30℃.

[0126] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 30min.

[0127] S4, secondary sintering, followed by heating to 175℃ at a rate of 4℃ / min, and holding for 70min;

[0128] S5, natural cooling, yields an asymmetric composite medium.

[0129] Example 6: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0130] S1, comprising material A and material B; wherein material A uses the same first particle as in Example 1, and material B comprises a second particle and a third particle, wherein the second particle is the same as in Example 1; the third particle has a weight-average molecular weight of 3 million, is UPE, and has a bulk density of 0.18 g / cm³. 3 The mass fraction of the third particle in material B is 20%; the mass ratio of material A to material B is 1:7.

[0131] S2, one-time sintering: First, material B is evenly loaded into the sintering mold and compacted. The temperature is first raised to 120℃ and held for 125 minutes at a rate of 5℃ / min. Then, the temperature is raised to 160℃ at a rate of 5℃ / min. After holding for 115 minutes, the temperature is cooled to 30℃.

[0132] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 40min.

[0133] S4, secondary sintering, followed by heating to 165℃ at a rate of 4℃ / min, and holding for 100min;

[0134] S5, natural cooling, yields an asymmetric composite medium.

[0135] Example 7: A process for preparing an asymmetric gradient sintering composite medium, comprising the following steps:

[0136] S1, equipped with material A and material B; wherein the first particle used in material A is the same as in Example 2, and material B includes a second particle and a third particle, wherein the second particle is the same as in Example 2; the third particle has a weight-average molecular weight of 4 million, is UPE, and has a bulk density of 0.22 g / cm3; the mass fraction of the third particle in material B is 30%; the mass ratio of material A to material B is 1:6;

[0137] S2, one-time sintering: First, material B is evenly loaded into the sintering mold and compacted. The temperature is first raised to 125℃ and held for 120 minutes at a rate of 6℃ / min. Then, the temperature is raised to 160℃ at a rate of 6℃ / min. After holding for 110 minutes, the temperature is cooled to 30℃.

[0138] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 130℃ at a heating rate of 5℃ / min, and then hold it for 40min;

[0139] S4, secondary sintering, followed by heating to 165℃ at a rate of 4℃ / min, and holding for 95min;

[0140] S5, natural cooling, yields an asymmetric composite medium.

[0141] Comparative Example 1: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0142] S1, equipped with material A and material B; wherein the first particle selected for material A is the same as that in Example 1, and the second particle selected for material B is the same as that in Example 1; the mass ratio of material A to material B is 1:7;

[0143] S2, one-time sintering: first, material B is evenly loaded into the sintering mold and compacted, then directly heated to 160℃ at a heating rate of 10℃ / min, then held for 30min, and then cooled to 30℃.

[0144] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 10min.

[0145] S4, secondary sintering, followed by heating to 160℃ at a rate of 10℃ / min, and holding for 20min;

[0146] S5, natural cooling, yields an asymmetric composite medium.

[0147] Compared to the sample prepared in Example 1, the sample prepared in Comparative Example 1 has an excessively large average pore size in terms of PMI, resulting in very low retention efficiency for 1 μm impurities and making it impractical.

[0148] Comparative Example 2: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0149] S1, equipped with material A and material B; wherein the first particle selected for material A is the same as that in Example 1, and the second particle selected for material B is the same as that in Example 1; the mass ratio of material A to material B is 1:7;

[0150] S2, one-time sintering: first, material B is evenly loaded into the sintering mold and compacted, then directly heated to 160℃ at a heating rate of 2℃ / min, then held for 220min, and then cooled to 30℃.

[0151] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 60min.

[0152] S4, secondary sintering, followed by heating to 190℃ at a rate of 2℃ / min, and holding for 180min;

[0153] S5, natural cooling, yields an asymmetric composite medium.

[0154] Compared to the sample prepared in Example 1, the sample prepared in Comparative Example 1 has very low porosity, very low air throughput, poor filtration efficiency, and is not practical.

[0155] Comparative Example 3: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0156] S1, equipped with material A and material B; wherein the first particle selected for material A is the same as that in Example 1, and the second particle selected for material B is the same as that in Example 1; the mass ratio of material A to material B is 1:7;

[0157] S2, one-time sintering: first, material B is evenly loaded into the sintering mold and compacted, then heated to 160℃ at a heating rate of 5℃ / min, then held for 100min, and then cooled to 30℃.

[0158] S3, secondary sintering, then uniformly load material A into the sintering mold and compact it, then heat it to 179℃ at a heating rate of 10℃ / min, and hold it for 90min.

[0159] S4, naturally cooled, yields an asymmetric composite medium.

[0160] Compared to the sample prepared in Example 1, the sample prepared in Comparative Example 3 has almost no composite layer, and its hardness and compressive strength are very low. The separation layer and the support layer can easily separate under a small external force, making it unable to retain impurities or perform backwashing to recover impurities, thus lacking practicality.

[0161] Table 1

[0162]

[0163]

[0164] Since the composite layer thickness of Example 7 in the table above does not fall within the protection range of a more preferred composite layer thickness, it will affect the overall flux to some extent, resulting in a slightly lower flux of the composite medium; at the same time, its hardness and compressive strength are almost not increased.

[0165] Table 2

[0166]

[0167] Table 3

[0168]

[0169]

[0170] The samples obtained in Examples 1-5 were subjected to retention performance tests (in fact, the particle size of the impurity particles used in Examples 1, 6, Comparative Examples 1 and 2 was 1 micrometer, the particle size of the impurity particles used in Examples 2 and 7 was 3 micrometer, the particle size of the impurity particles used in Example 3 was 5 micrometer, the particle size of the impurity particles used in Example 4 was 10 micrometer, and the particle size of the impurity particles used in Example 5 was 20 micrometer), airflow tests, pressure resistance tests, and Shore A hardness tests. The test results are shown in Table 4 below:

[0171] Retention efficiency Flux L / min@7kpa Pressure resistance / N Shore A hardness / HA Example 1 Greater than 90% 520 500 93 Example 2 Greater than 90% 710 480 90 Example 3 Greater than 90% 950 460 87 Example 4 Greater than 90% 1260 440 84 Example 5 Greater than 90% 1700 400 80 Example 6 Greater than 90% 620 495 92 Example 7 Greater than 90% 820 475 89 Comparative Example 1 25％ 580 250 65 Comparative Example 2 Greater than 90% 100 460 90

[0172] As shown in the table above, the composite media prepared in Examples 1-5 have suitable pore size and porosity, which enables them to effectively capture impurities of a certain particle size, ensuring retention efficiency. They also have good throughput, high hardness, and high compressive strength. Compared to Example 1, Example 6 added a third particle during sample preparation, which significantly improved the throughput of the composite media, but the retention efficiency, hardness, and compressive strength remained almost unchanged. Compared to Example 2, Example 7 added a third particle during sample preparation, which significantly improved the throughput of the composite media, but the retention efficiency, hardness, and compressive strength remained almost unchanged.

[0173] Example 8: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0174] S1, equipped with material A and material B; wherein the first particle selected for material A is the same as that in Example 1, and the second particle selected for material B is the same as that in Example 1; the mass ratio of material A to material B is 1:7;

[0175] S2, one-time sintering: first, material B is evenly loaded into the sintering mold and compacted, then directly heated to 160℃ at a heating rate of 5℃ / min, then held for 120min, and then cooled to 30℃.

[0176] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 50min.

[0177] S4, secondary sintering, followed by heating to 180℃ at a rate of 2℃ / min, and holding for 105min;

[0178] S5, natural cooling, yields an asymmetric composite medium.

[0179] Compared to the sample prepared in Example 1 (the average SEM particle size of the first particle was 12 μm and the average SEM particle size of the second particle was 200 μm), the sample prepared in Example 8 was ultimately tested and found to have an average SEM particle size of 4.5 μm for the first particle and 180 μm for the second particle, with a ratio of 40 between the average SEM particle size of the second particle and the average SEM particle size of the first particle. The smaller particle size of the first particle resulted in a gas flow rate of 300 L / min at 7 kPa for the sample prepared in Example 8, which was significantly lower than that of the sample prepared in Example 1. At the same time, it was found that if the sample was backwashed, the first particle was relatively easy to detach, which would affect the purity of the fluid and shorten the service life of the composite medium.

[0180] Example 9: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0181] S1, equipped with material A and material B; wherein the first particle selected for material A is the same as that in Example 1, and the second particle selected for material B is the same as that in Example 1; the mass ratio of material A to material B is 1:7;

[0182] S2, one-time sintering: first, material B is evenly loaded into the sintering mold and compacted, then directly heated to 160℃ at a heating rate of 5℃ / min, then held for 100min, and then cooled to 30℃.

[0183] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 5℃ / min, and then hold it for 30min.

[0184] S4, secondary sintering, followed by heating to 170℃ at a rate of 5℃ / min, and holding for 70min;

[0185] S5, natural cooling, yields an asymmetric composite medium.

[0186] Compared to the sample prepared in Example 1 (with an average SEM width of 10 μm for the connection nodes and a composite layer thickness of 100 μm), the sample prepared in Example 9, after testing, showed almost no connection nodes on its cross-section. Furthermore, the composite layer thickness was only 45 μm. Consequently, the sample prepared in Example 9 had a compressive strength of 470 N and a Shore A hardness of 85 HA, which were significantly lower than those of the sample prepared in Example 1, posing certain problems during high-pressure backwashing.

[0187] Example 10: A preparation process for an asymmetric gradient sintering composite medium, comprising the following steps:

[0188] S1, equipped with material A and material B; wherein the first particle selected for material A is the same as that in Example 1, and the second particle selected for material B is the same as that in Example 1; the mass ratio of material A to material B is 1:2;

[0189] S2, one-time sintering: first, material B is evenly loaded into the sintering mold and compacted, then directly heated to 160℃ at a heating rate of 10℃ / min, then held for 100min, and then cooled to 30℃.

[0190] S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 135℃ at a heating rate of 10℃ / min, and then hold it for 30min.

[0191] S4, secondary sintering, followed by heating to 175℃ at a rate of 10℃ / min, and holding for 90min;

[0192] S5, natural cooling, yields an asymmetric composite medium.

[0193] Compared to the sample prepared in Example 1 (separation layer thickness of 2 mm, overall thickness of 15 mm), the separation layer in Example 10 was thicker (6 mm) and the overall thickness was 15 mm due to the higher amount of material A used in the separation layer. The ratio of the separation layer thickness to the composite medium thickness was 40%, resulting in a gas flow rate of 350 L / min@7 kPa for the sample prepared in Example 8, which was significantly lower than that of the sample in Example 1, while the retention efficiency did not improve significantly. At the same time, it was found that the retained impurities were difficult to backwash out during backwashing, and the recovery rate of impurities was very low, which was not conducive to the recovery of catalyst and precious metals.

[0194] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. An asymmetric gradient sintering composite medium, comprising a body having non-directional tortuous pathways within the body, characterized in that: The main body includes a support layer, a composite layer, and a separation layer for trapping various fine substances; the composite layer is located between the support layer and the separation layer; the average pore size of the separation layer is smaller than the average pore size of the support layer; The separation layer includes first particles for forming a porous structure; the support layer includes second particles for forming a porous structure; the composite layer includes first and second particles for forming a porous structure; both the first and second particles are polyethylene-based materials. The thickness of the composite layer is not less than 0.1 μm, and the crystallinity of the separation layer is 40%-85%. The composite medium has an average PMI pore size of 0.1-25 μm and an overall porosity of 25%-75%.

2. The asymmetric gradient sintering composite medium according to claim 1, characterized in that: The average SEM particle size of the first particle is 5-60 μm, and the average SEM particle size of the second particle is 80-500 μm.

3. The asymmetric gradient sintering composite medium according to claim 1, characterized in that: The thickness of the composite layer is 1-1000 μm; Within the composite layer, a connection node is formed between the first particle and the second particle, and the SEM average width of the connection node is 3-50 μm.

4. The asymmetric gradient sintering composite medium according to claim 3, characterized in that: The thickness of the composite layer is 10-800 μm.

5. The asymmetric gradient sintering composite medium according to claim 3, characterized in that: The thickness of the composite layer is 50-500 μm.

6. The asymmetric gradient sintering composite medium according to claim 3, characterized in that: The ratio of the average SEM particle size of the second particle to the average SEM particle size of the first particle is 5-30. The ratio of the average SEM width of the connecting node to the average SEM particle size of the first particle is 1:1.1-4.

7. The asymmetric gradient sintering composite medium according to claim 1, characterized in that: The thickness of the separation layer is 0.1-5 mm, and the ratio of the thickness of the separation layer to the thickness of the composite medium is 0.01-0.

2.

8. The asymmetric gradient sintering composite medium according to claim 1, characterized in that: The distribution density of the second particle is 1-30 particles / mm. 2 The composite medium has a basis weight of 0.5-1.2 g / cm³. 2 .

9. The asymmetric gradient sintering composite medium according to claim 1, characterized in that: The support layer also includes a third particle, which is a polyethylene material, and the SEM average particle size of the third particle is 8-80 μm.

10. The asymmetric gradient sintering composite medium according to claim 9, characterized in that: The ratio of the average SEM particle size of the second particle to the average SEM particle size of the third particle is 5-35:1; and the average SEM particle size of the third particle is greater than the average SEM particle size of the first particle.

11. The asymmetric gradient sintering composite medium according to claim 1, characterized in that: The surface of the separation layer facing away from the support layer is the first surface, and the surface of the support layer facing away from the separation layer is the second surface. The porosity of the second surface is 10%-70%. The ratio of the pore area ratio of the first surface to the pore area ratio of the second surface is 0.3-0.9:

1.

12. The asymmetric gradient sintering composite medium according to claim 11, characterized in that: The first surface has a plurality of mold wall contact areas, the SEM average width of the mold wall contact areas is 5-35 μm; the area ratio of the mold wall contact areas is 10%-65%; The area ratio of the mold wall contact area is equal to the SEM area of ​​the mold wall contact area / the SEM area of ​​the first surface.

13. The asymmetric gradient sintering composite medium according to claim 1, characterized in that: The thickness of the composite medium is 10-50 mm; The composite medium has a rejection efficiency of no less than 80% for impurity particles with a particle size of 1-20 micrometers. The flux of the composite medium is 200-2000 L / min, and the test pressure is 7 kPa; The Shore A hardness of the composite medium is not less than 70HA.

14. The preparation process of an asymmetric gradient sintering composite medium according to claim 1, characterized in that: Includes the following steps: S1, equipped with material A and material B; Material A contains a first particle with a weight-average molecular weight of 3 million to 8 million, the first particle being UPE, and the particle size of the first particle being less than 100 μm. Material B contains a second particle with a weight-average molecular weight of 200,000 to 800,000, the second particle is HDPE, and the particle size of the second particle is greater than 200 μm. S2, one-time sintering: first, material B is evenly loaded into the sintering mold and compacted, then the temperature is raised to 150-180℃ at a rate of 3-10℃ / min, then held for 80-120min, and then cooled to 20-40℃. S3, pretreatment, then uniformly load material A into the sintering mold and compact it, then heat it to 110-140℃, and then hold it for 20-50 minutes; S4, secondary sintering, followed by heating to 150-180℃, with the holding time being 70%-95% of the holding time in S2; S5, natural cooling, yields an asymmetric composite medium.

15. The preparation process of an asymmetric gradient sintering composite medium according to claim 14, characterized in that: Material B further comprises a third particle with a weight-average molecular weight of 2 million to 6 million, wherein the third particle is UPE and its bulk density is 0.15-0.25 g / cm³. 3 The mass fraction of the third particle in material B is 10%-40%.

16. The preparation process of an asymmetric gradient sintering composite medium according to claim 14, characterized in that: In the first sintering of S2, the temperature is first raised to 110-140℃, and the holding time is 2-5 times that of S3. Then the temperature is raised to 150-180℃.

17. The preparation process of an asymmetric gradient sintering composite medium according to claim 14, characterized in that: The mass ratio of material A to material B in S1 is 1:3-8; the heating rate in S3 is 3-10℃ / min; the heating rate in S4 is 60%-90% of the heating rate during the first sintering in S2.

18. The application of an asymmetric gradient sintering composite medium as described in any one of claims 1-13, characterized in that, The composite medium is used for the recovery of catalysts and precious metals.

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