An asymmetric PES filter membrane, a preparation method thereof and a filter assembly

Abstract

This invention relates to an asymmetric PES filter membrane, its preparation method, and a filtration assembly. The membrane comprises a porous body with non-directional tortuous pathways. One side of the porous body is a first outer surface, and the other side is a second outer surface. The porous body includes a pre-filtration layer, a separation layer, and a support layer. The average pore size measured by SEM of the support layer is larger than that measured by SEM of the separation layer. The average PMI pore size of the filter membrane is 0.15–0.6 μm. The second outer surface has effluent pores and macropores. The average pore size D2 of the effluent pores is 0.4–2.0 μm, and the average pore size D of the macropores is… 大孔 The porosity of the second outer surface is not less than 1.5D2, the surface porosity coefficient I of the second outer surface is 13%-30%, and the density ρ of the macropores on the second outer surface is not less than 1.5D2. 大孔 80-200 per 10000μm 2 The second outer surface of the filter membrane has appropriate pore size and number of liquid outlet holes and macropores, so that after the filter membrane is introduced into the support layer, the internal resistance of the filter membrane only increases slightly while the external resistance decreases significantly, ensuring that the flux of the filter membrane is significantly improved in actual use.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and more specifically to an asymmetric PES filter membrane, its preparation method, and a filtration assembly. Background Technology

[0002] Various biopharmaceutical products may contain bacteria due to contamination from raw materials or introduction during production. If these bacteria are not eliminated and the product is used directly, serious safety issues will arise. Therefore, appropriate sterilization and / or disinfection processes are essential in the production of all biopharmaceuticals. Common sterilization methods include high-temperature sterilization and radiation sterilization. While these methods offer good sterilization effects and high efficiency, both can easily lead to the inactivation of active substances. For biopharmaceuticals containing active substances, this means a decrease in efficacy or even complete failure, a highly unacceptable drawback. Compared to conventional sterilization methods, membrane separation sterilization technology is widely used in the biopharmaceutical field due to its advantages such as low pollution, high separation efficiency, low energy consumption, no need for external chemical reagents, ability to separate systems that conventional methods cannot (such as azeotropic systems), and mild separation conditions that are less likely to cause changes in the properties of active substances.

[0003] Currently, the main membrane materials used for bacterial filtration include nylon, PTFE, PVDF, and PES. Among them, PES material has excellent mechanical properties, superior heat resistance, alkali resistance, corrosion resistance, and gamma ray irradiation resistance, making it particularly suitable for fields with complex working conditions such as biopharmaceuticals. Therefore, PES filter membranes play a very important role in fields such as biopharmaceuticals.

[0004] For example, Chinese invention patent application CN1748847A (application by Zhejiang University) discloses a method for preparing a symmetrical polyethersulfone hydrophilic microporous membrane. The polyethersulfone microporous membrane prepared by this method has advantages such as symmetrical structure, hydrophilicity, and strong temperature resistance. In order to ensure good retention of impurities in the feed solution, this symmetrical PES filter membrane should not have an excessively large pore structure. However, a smaller pore structure causes large particles of impurities in the feed solution to be concentrated and retained near the inlet surface, which quickly clogs the pore structure of the filter membrane. Therefore, symmetrical filter membranes often have a lower dirt holding capacity (low load) and a lower flux (low filtration efficiency).

[0005] Compared to symmetrical filter membranes, asymmetrical filter membranes often exhibit better loading and retention effects due to their larger pore regions with greater dirt-holding capacity and smaller pore regions with better retention efficiency, thus leading to their rapid development. For example, European patent document EP1149624B1 (applied by Parr) discloses a highly asymmetric anion exchange membrane, which can be an ultrafiltration membrane with an average flow pore size of less than about 0.1 μm, about 0.2 μm, or about 0.3 to about 1.0 μm. The membrane can be asymmetric, and the pores on the first surface can be at least about 5 times smaller than those on the second surface. The diameter of the flow channels in the porous support structure gradually increases from the first surface to the second surface.

[0006] The macropore region (the region near the second surface) of the typical V-shaped asymmetric filter membrane disclosed in the aforementioned patent has a larger dirt-holding capacity, which can pre-intercept and accommodate large particulate impurities in the feed liquid, greatly reducing the possibility of large particulate impurities clogging the membrane pore structure; while the micropore region (the region near the first surface) of the asymmetric filter membrane can intercept bacteria in the feed liquid, ensuring a low risk of bacterial leakage; thus, it has a high loading capacity and interception effect. However, when using sterilizing filter membranes, they often need to be placed in a container to form a membrane filter. In order to avoid excessive deformation and damage to the filter membrane during use, which may cause the risk of bacterial leakage, it is often necessary to set a support structure for supporting the filter membrane downstream of the filter membrane or to laminate the filter membrane with a reinforcing layer (such as non-woven fabric) to form a membrane module for use.

[0007] For example, Chinese utility model patent document CN202155092U discloses a needle filter, including an inlet pipe, an outlet pipe, a filter disc, and a filter membrane. The filter disc is disc-shaped and includes a top plate, a bottom plate, and sidewalls for forming a accommodating space. The top plate is connected to the inlet pipe, and the bottom plate is connected to the outlet pipe. A guide block is provided on the bottom plate to support the filter membrane and form a feed channel. While the guide block does reduce membrane deformation, the presence of the guide block, non-woven reinforcing layer, etc., inevitably leads to a decrease in flux. This may be because the pore size of typical V-shaped asymmetric filter membranes gradually decreases along the feed flow direction, resulting in the smallest pore size and lowest pore area ratio at the outlet surface, which is naturally the area with the greatest impact on flux. Both the fiber structure of the nonwoven fabric and the flow guide block are much larger than the pore size of the filter membrane's outlet surface. When the filter membrane's outlet surface is tightly adhered to the flow guide block or nonwoven fabric under upstream feed pressure, some of the pores on the outlet surface are inevitably completely blocked by the flow guide block or nonwoven fabric fibers. This results in a significant reduction in the number of effective pores for feed flow on the outlet surface, and consequently, a significant decrease in the filter membrane's flux. Therefore, although typical V-type asymmetric filter membranes have high loading capacity and good bacterial retention performance, their flux is often low in actual use.

[0008] In summary, obtaining a filter membrane that not only has high loading capacity and good bacterial retention performance, but also high flux in practical use is currently a technical challenge. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the present invention aims to provide an asymmetric PES filter membrane, its preparation method, and a filter assembly. This filter membrane exhibits high bacterial filtration performance and high dirt-holding capacity (high loading capacity). Furthermore, in practical use, the filter membrane also possesses high flux. To achieve the above objectives, the present invention provides the following technical solution:

[0010] In a first aspect, this application provides an asymmetric PES filter membrane, employing the following technical solution:

[0011] An asymmetric PES filter membrane includes a porous body with non-directional tortuous pathways within it. One side of the porous body is a first outer surface, and the other side is a second outer surface. The porous body includes a pre-filtration layer, a separation layer for retaining bacteria, and a support layer. One side of the pre-filtration layer is the first outer surface, and one side of the support layer is the second outer surface. The pre-filtration layer, separation layer, and support layer are connected by continuous fibers. The average pore size of the support layer measured by SEM is larger than that of the separation layer measured by SEM. The average pore size (PMI) of the filter membrane is 0.15-0.6 μm.

[0012] The second outer surface has a plurality of liquid outlet holes, the SEM average pore diameter D2 of which is 0.4-2.0 μm; the second outer surface also has a plurality of macropores, the pore diameter D of which is... 大孔 Not less than 1.5D2; the surface porosity coefficient I of the second outer surface is 13%-30%, and the surface porosity coefficient I is calculated by the following formula: I=(ρ 大孔 / ρ)×100%, where ρ 大孔 ρ represents the density of macropores on the second outer surface; ρ represents the density of effluent pores on the second outer surface, in units of pores / 10000μm. 2 The density ρ of the macropores on the second outer surface 大孔 80-200 per 10000μm 2 .

[0013] By adopting the above technical solution, the PES filter membrane of this application has non-directional tortuous pathways in its main body. These non-directional tortuous pathways refer to randomly oriented groove structures and / or discretely distributed pore structures, and each non-directional tortuous pathway is interconnected. The filter membrane in this application has an asymmetrical membrane structure. Along its thickness direction, a pre-filtration layer, a separation layer, and a support layer can be seen sequentially. The pre-filtration layer, separation layer, and support layer are transitioned by continuous fibers. "Continuous" means that essentially all fibers are integrally connected to each other, as if formed as a single piece, without the need for additional adhesives or the like to connect them. Unless torn by external force, the network of fibers cannot be separated from each other. The pre-filtration layer is used to intercept large particulate impurities in the feed liquid, preventing large particulate impurities from clogging the separation layer, thereby increasing the service life of the sterilization membrane. The separation layer is used to intercept bacteria. The filter membrane of this application can be used in single or multiple layers depending on the actual required interception effect.

[0014] The filter membrane of this application, based on a two-layer structure, introduces a support layer with a larger pore size than the separation layer. Along the thickness direction of the filter membrane, the overall pore size of the filter membrane first gradually decreases and then gradually increases. It is generally believed that the additional support layer has a relatively large pore structure and relatively low feed resistance. However, the introduction of the support layer means an extension of the tortuous path inside the filter membrane, which inevitably increases the internal resistance to the feed, thus leading to a further decrease in the filter membrane flux. However, the inventors of this application unexpectedly discovered that the filter membrane provided by this application still has a high flux in actual use.

[0015] This is likely because the factors affecting the filter membrane's resistance to feed liquid are not limited to the membrane's internal resistance, but also include its external resistance. External resistance refers to the resistance to feed liquid flow caused by external factors, such as the increased resistance due to the shielding of the membrane's pore structure by the supporting structure. For example, in the case of a V-shaped asymmetric membrane, if some of the pores at the membrane's outlet surface are blocked, the number of effective pores supplying feed liquid to the outlet surface will be significantly reduced, resulting in a substantial increase in the membrane's external resistance and a significant decrease in its flux.

[0016] This application introduces a support layer with a larger pore size than the separation layer on top of a two-layer filter membrane. Admittedly, the introduction of the support layer increases the thickness of the filter membrane and lengthens the tortuous pathways within it, leading to an increase in internal resistance. However, the filter membrane in this application, after introducing the support layer, has pores with a suitable pore size (D2 of 0.4-2.0 μm) on the liquid outlet surface. Furthermore, the liquid outlet surface has large pores of suitable size, number, and density, minimizing the increase in internal resistance after the introduction of the support layer and maximizing the decrease in external resistance. Moreover, a suitable number of large pores often implies a suitable number of small pores. These small pores compensate for the mechanical losses caused by the introduction of large pores, ensuring that the liquid outlet surface still possesses high mechanical strength. This prevents excessive deformation of the porous structure near the liquid outlet surface during actual use, thus ensuring a significant increase in filter flux. This application specifies the density ρ of the large pores on the liquid outlet surface. 大孔 The appropriate macropore density (ρ) is determined by limiting the porosity I at the liquid surface. 大孔 80-200 per 10000μm 2 The porosity coefficient I represents the number of macropores on the liquid outlet surface per unit area, i.e., the number of macropores; I is calculated using the following formula: I=(ρ 大孔 / ρ)×100%, the liquid outlet surface has a suitable porosity I (surface porosity I is 13%-30%) and a suitable macropore density ρ. 大孔 This also means that the liquid outlet surface has an appropriate number of liquid outlet holes.

[0017] The second outer surface of the filter membrane (the liquid outlet surface) has a suitable number and size of liquid outlet pores (the average SEM pore size D2 of the liquid outlet pores is 0.4-2.0 μm). This, to some extent, means that a suitable number and size of large pores have been introduced into the liquid outlet surface. The suitable pore structure and large pore structure of the liquid outlet surface significantly increase the number of effective pore structures and the effective pore channel area for the feed liquid flow. Even if some pores on the liquid outlet surface are blocked, the number of effective pore structures for the feed liquid flow remains relatively large, and the effective pore channel area remains relatively large, ensuring high fluidity of the feed liquid within the filter membrane. In other words, the external resistance of the filter membrane is significantly reduced after the introduction of the support layer. In actual use, the impact of reduced external resistance on the filter membrane flux is far greater than the impact of increased internal resistance on the filter membrane flux. Therefore, the filter membrane flux is significantly improved.

[0018] If the average pore size of the outlet holes is too small (less than 0.4 μm), it means that the overall pore size and effective flow channel area of ​​the outlet surface are small, resulting in a relatively high overall density of the outlet surface. The density of the outlet surface is defined as the ratio of the area of ​​the solid portion of the outlet surface per unit area of ​​the membrane to the total area of ​​the outlet surface. This high density and relatively small effective flow channel area may lead to a significant increase in the internal resistance of the filter membrane after the introduction of the support layer, while the reduction in external resistance is limited. In actual use, the internal resistance has a greater impact on the filter membrane flux than the external resistance, resulting in a decrease in actual flux. Conversely, if the average pore size of the outlet holes is too large (greater than 2.0 μm), it means that the overall pore size of the outlet surface is too large (especially D...). 大孔 The overall density of the outlet surface is relatively low, and the mechanical properties of the porous matrix near the outlet surface are also relatively low. Since high filtration pressure is required to ensure high filtration efficiency, under high pressure, the porous matrix near the outlet surface of the filter membrane with low mechanical properties may deform excessively, causing some pores to collapse. This reduces the reduction in external resistance and significantly increases internal resistance, resulting in a significant decrease in the filter membrane's flux.

[0019] With an average pore size D2 of 0.4-2 μm at the outlet surface, an excessive number of large pores indicates poor overall uniformity of the outlet pores, meaning there are often a large number of smaller pores. These smaller pores have lower feed throughput; in other words, once the large pores are blocked, the change in external resistance of the filter membrane will increase significantly. In practical use, blockage of the large pores is unavoidable because the size of the supporting structure in contact with the outlet surface is much larger than the pore size, sometimes by orders of magnitude. An excessive number of large pores at the outlet surface also means an excessive number of smaller pores. Blockage of the large pores reduces the reduction in external resistance of the filter membrane, while the presence of smaller pores does not significantly aid feed flow. The combined effect of these two factors actually reduces the filter membrane's flux. Furthermore, if there are too many large pores on the liquid outlet surface, it often means that the mechanical properties of the porous body near the liquid outlet surface are relatively insufficient. The porous body near the liquid outlet surface may be excessively deformed, causing some pores to collapse. This reduces the reduction in the external resistance of the filter membrane while significantly increasing the internal resistance of the filter membrane, thereby leading to a significant reduction in the flux of the filter membrane.

[0020] If the number of large pores on the liquid outlet surface is too small, it indicates that the overall pores on the liquid outlet surface are relatively uniform. While this certainly implies that the liquid outlet surface possesses high mechanical properties, a small number of large pores often also means that the density of the liquid outlet surface is relatively high. This is because, for a single liquid outlet, if it is approximated as circular, and the diameter of the liquid outlet becomes twice its original size, then the pore area (the area of ​​the flow channel for the feed liquid) of the liquid outlet may become four times or even higher. Even if the average pore diameter D2 of the liquid outlet surfaces of two filter membranes is the same, if one filter membrane has a certain number of large pores on its liquid outlet surface, while the overall pore diameter of the other filter membrane is relatively uniform, then the filter membrane with a certain number of large pores on its liquid outlet surface will have a lower density. Therefore, the introduction of an appropriate number of large pores further reduces the density of the liquid outlet surface, resulting in only a small increase in the overall internal resistance of the filter membrane while significantly reducing the external resistance. This differs from the commonly understood support layer structure that serves a "protective" function. For example, Chinese patent application CN113117537A also discloses a PES filter membrane with an introduced "support layer." However, in actual use, the flux of such a membrane is not high. This may be because the support layer introduced in the aforementioned patent serves a "protective" function. Generally, the presence of large pores on the liquid outlet surface means that the proportion of the solid portion of the porous body near the large pores on the liquid inlet surface is relatively small, and the resistance of this solid portion to mechanical damage is often low. Therefore, to improve the "protective" effect of the support layer on the separation layer, the pore structure of the liquid outlet surface is often adjusted to minimize the number of large pores near the liquid outlet surface. This undoubtedly reduces the flux of the filter membrane in actual use.

[0021] As mentioned above, to ensure high flux of the filter membrane in practical use, it is first necessary to ensure that the outlet surface has low density, a large number of effective pore structures, and a relatively large effective pore channel area. This means that after the introduction of the support layer, the internal resistance of the filter membrane only increases slightly, while the external resistance decreases significantly. However, if the density of the outlet surface is too low, although theoretically the internal resistance of the support layer is low, and because the effective flow area of ​​the outlet surface is relatively large, even the partially shielded portion will have a significant decrease in external resistance, in actual use, the feed liquid needs to be pressurized as the driving force. Under pressure, the already large and low-strength pore structures are prone to collapse, and the internal resistance brought by the support layer will actually be relatively large. Therefore, to ensure a significant increase in the flux of the filter membrane in practical use, it is also necessary to ensure that the outlet surface of the filter membrane has appropriate mechanical strength, so as to prevent excessive deformation of the porous structure near the relatively low-density outlet surface.

[0022] In summary, this application controls the pore size, number of pores, pore size, and number of macropores on the liquid outlet surface of the filter membrane, resulting in a lower density, a greater number of effective pore structures, and a larger effective pore flow area. This significantly reduces the increase in internal resistance of the filter membrane and significantly increases the decrease in external resistance. At the same time, the porous body of the liquid outlet surface of the filter membrane also has high mechanical strength, preventing excessive deformation during actual use. Under the combined effect of the above features, the flux of the filter membrane is significantly improved in actual use.

[0023] It is worth noting that the filter membrane of this application is particularly suitable for use in multilayer filter membrane stacks as membrane modules. This is likely because, in actual use, the solid portion of the inlet surface of the downstream filter membrane inevitably blocks the pores of the outlet surface of the upstream filter membrane. Once the pores of the outlet surface of the upstream filter membrane are blocked, the external resistance of the filter membrane will undoubtedly increase, leading to a significant decrease in the filter membrane flux. However, with the filter membrane of this application, even if the outlet pores of the upstream filter membrane are partially blocked, the upstream filter membrane still has a high flux, thereby ensuring that the overall membrane module has a high flux.

[0024] Furthermore, for filter membranes, high retention capacity and high throughput are often mutually exclusive. This is because filter membranes with high retention capacity tend to have high retention capacity for the feed liquid, and vice versa. However, this application, by introducing a support layer with a specific liquid outlet structure, achieves both high retention capacity and high throughput for the filter membrane without significantly adjusting the structure of the separation layer, thereby altering the internal and external resistance of the filter membrane. This is also unexpected.

[0025] In this application, pores distributed on the second outer surface with a pore size of 0.05-5 μm are defined as liquid outlet pores. The PES filter membrane of this invention is mainly used for bacterial filtration. Generally speaking, the diameter of bacteria is 0.5~5 μm. Pores smaller than 0.05 μm are orders of magnitude different from the diameter of bacteria. Therefore, pores smaller than 0.05 μm can be considered dense. If the pore size is larger than 5 μm, the excessively large pores may lead to bacterial leakage. Therefore, pores with a pore size larger than 5 μm on the liquid outlet surface cannot be defined as liquid outlet pores, and may even be defined as defects.

[0026] When measuring the pore size of the liquid outlet, the second outer surface of the membrane can be characterized using a scanning electron microscope (SEM) to obtain the corresponding SEM image, and a certain area, such as 1000 μm, can be selected. 2 (20μm x 50μm) or 2500μm 2(50μm x 50μm), the specific area size depends on the actual situation. Then, use appropriate computer software or manually to measure the number and diameter of the liquid outlet holes on this area, and calculate their average value to obtain the average pore diameter D2 of the liquid outlet holes. 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. After obtaining the average pore diameter D2 of the liquid outlet holes, the number of macropores on this area can be measured using computer software or manually, and the density ρ of the macropores can be further calculated. 大孔 The density ρ of the pores on the second outer surface can also be obtained using a similar method; furthermore, the porosity I of the second outer surface can be calculated using the following formula: I = (ρ 大孔 / ρ)×100%.

[0027] The average pore size of the sterilization membrane (PMI) can be directly measured using a PMI pore size tester.

[0028] Optionally, the pore area ratio of the liquid outlet is 4-18%, and the density ρ of the liquid outlet is 450-950 per 10000 μm. 2 .

[0029] By adopting the above technical solution, the liquid outlet holes on the liquid outlet surface have a suitable pore area ratio and density, indicating that the liquid outlet surface as a whole has a suitable density and suitable mechanical strength. This further ensures that after the filter membrane is introduced into the support layer, the internal resistance of the filter membrane only increases slightly, while the external resistance of the filter membrane decreases significantly, further ensuring the significant improvement of the filter membrane in actual use.

[0030] If the pore area ratio at the liquid outlet is too small (less than 4%) and / or the pore density at the liquid outlet is too small (ρ < 450 pores / 10000μm) 2 This means that the density of the filter membrane at the liquid outlet is relatively high. Even with the introduction of a suitable number and size of macropores after the introduction of the support layer, the internal resistance of the filter membrane still increases significantly, while the external resistance decreases less. This may result in a limited increase in flux during actual use, or even a decrease in flux. If the pore area ratio at the liquid outlet is too large (greater than 18%) and / or the pore density at the liquid outlet is too large (ρ > 950 pores / 10000μm), further problems may occur. 2The relatively low density of the liquid outlet surface, although this means that the introduction of the support layer results in a smaller increase in the internal resistance of the filter membrane itself, also means that the mechanical properties of the porous body near the liquid outlet surface are relatively low. Under the action of the feed liquid pressure, it is easy to cause excessive deformation of some pores on the liquid outlet surface of the filter membrane, or even some pores to collapse. This will reduce the reduction in the external resistance of the filter membrane and increase the internal resistance of the filter membrane, thus limiting the increase in the flux of the filter membrane, or even causing a decrease in flux.

[0031] The liquid outlet surface has a suitable pore size (0.4-2.0μm) and a suitable number of outlet pores (450-950 per 10000μm). 2 Furthermore, the liquid outlet surface has a suitable pore area ratio (4-18%), and in addition, the liquid outlet surface also has a suitable number (80-200 pores / 10000μm). 2 Furthermore, the appropriately sized pores minimize the density of the liquid outlet surface while ensuring the overall mechanical strength of the surface. In other words, through the combined synergistic effect of these three factors, the increase in the internal resistance (actual internal resistance) of the filter membrane after the introduction of the support layer is minimized, while the decrease in the external resistance of the filter membrane is maximized, resulting in a significant increase in flux during actual use.

[0032] Understandably, the porosity of the second outer surface (liquid outlet surface) can be obtained by using a scanning electron microscope to characterize the morphology of the second outer surface of the filter membrane, selecting a certain area, measuring the area of ​​all the pores on that area, and then calculating the porosity of the second outer surface.

[0033] Optionally, the second outer surface is provided with a plurality of extra-large holes, wherein the diameter D of the extra-large holes is... 特大孔 The pore density ρ of the extra-large pore is not less than 3D2. 特大孔 No more than 20 per 10000μm 2 .

[0034] By adopting the above technical solution, the inventors of this application unexpectedly discovered that when there are only a few extra-large pores on the second outer surface (liquid outlet surface), the flux of the filter membrane will be further improved during actual use.

[0035] This may be because, firstly, the presence of extra-large pores means that the proportion of non-solid parts in the porous matrix near the extra-large pores is relatively large, resulting in relatively low mechanical properties of the porous matrix near the extra-large pores; if the number of extra-large pores is too large (e.g., greater than 20 per 10000 μm)... 2If the overall mechanical properties of the liquid surface are relatively low, it indicates that there are too many areas with low mechanical properties. Under the action of liquid pressure, the probability of excessive deformation or even pore collapse of the porous body near each extra-large hole is relatively high. Once it is excessively deformed or even collapses, it will lead to a significant increase in the internal resistance of the filter membrane and a decrease in the reduction of the external resistance of the filter membrane.

[0036] Secondly, based on the determined average pore diameter D2 of the liquid outlet, the existence of extra-large pores also implies, to some extent, the existence of a certain number of "extra-small pores" with relatively small pore diameters. The existence of "extra-small pores" means that after the filter membrane is introduced into the support layer, the internal resistance of the filter membrane increases significantly. However, in actual use of the filter membrane, it is unavoidable that the "extra-large pores" will be blocked. Once the "extra-large pores" are blocked, the decrease in the external resistance of the filter membrane will also be reduced, further affecting the flux of the filter membrane.

[0037] In summary, the presence of too many extra-large pores can actually lead to a significant increase in the internal resistance of the filter membrane while only a slight decrease in the external resistance, resulting in a limited increase in membrane flux and potentially even a decrease in flux. In this application, the filter membrane's outlet surface has outlet pores and macropores of suitable size, number, and density, with only a very small number of extra-large pores. The combined effect of these three factors further ensures that the porous structure near the outlet surface of the filter membrane possesses suitable density and mechanical strength, thereby guaranteeing high flux during actual use.

[0038] Optionally, the thickness h of the support layer is 10-20 μm, and the ratio of the thickness h of the support layer to the thickness H of the porous body is 0.1-0.18.

[0039] By adopting the above technical solution, the support layer has a suitable thickness. Combined with the liquid outlet holes and macropores of a specific size, number and density on the liquid outlet surface, the three factors work together to ensure that the support layer as a whole has high mechanical strength and the liquid outlet surface has low density. This further ensures that the introduction of the support layer results in only a slight increase in the internal resistance of the filter membrane and a significant reduction in the external resistance, leading to a significant improvement in the filter membrane flux.

[0040] Since the outlet surface has several macropores and extra-large pores, if the support layer is too thin (below 10 μm and / or h:H < 0.1), it indicates that the overall mechanical properties of the support layer are relatively insufficient. Under the pressure of the feed liquid, the area near the macropores and extra-large pores of the filter membrane is prone to excessive deformation, leading to a relatively high probability that its internal resistance will increase significantly while its external resistance will only decrease slightly, thus limiting the improvement in filter membrane flux. If the support layer is too thick (e.g., thicker than 20 μm and / or h:H > 0.18), and the average pore size D2 of the outlet surface is relatively small, it means that the introduction of the support layer will result in a relatively large increase in the overall internal resistance of the filter membrane. Even if several macropores and extra-large pores are introduced into the outlet surface, the overall internal resistance of the filter membrane will still increase significantly, which may prevent a significant improvement in filter membrane flux.

[0041] Optionally, the ratio of the SEM average pore size D2 of the liquid outlet to the thickness h of the support layer is 0.04-0.12 μm / μm.

[0042] For the filter membrane of this application, the pore size D2 of the liquid outlet and the thickness h of the support layer must be strictly controlled. This is because the pore size D2 of the liquid outlet also affects the pore size of macropores and extra-large pores. The presence of macropores and extra-large pores often means a loss of mechanical properties of the porous body (liquid outlet surface) near the macropores and extra-large pores. If the ratio between the pore size D2 of the liquid outlet on the second outer surface and the thickness h of the support layer is too large (D2:h > 0.12 μm / μm), it indicates that the pore size D2 of the liquid outlet is relatively large and / or the thickness h of the support layer is relatively thin. This means that the support layer is thin overall and the pore size is too large, the macropores and extra-large pores are too large, the mechanical properties of the support layer are insufficient, and under the action of the feed liquid pressure, the pore structure of the support layer is excessively deformed or even collapsed, resulting in a significant increase in the internal resistance of the filter membrane while the external resistance only decreases slightly. The probability of this is relatively high, meaning that the filter membrane flux cannot be significantly improved. If the ratio is too small (D2:h < 0.04 μm / μm), it means that the pore size D2 of the liquid outlet is relatively small and / or the thickness h of the support layer is relatively thick. That is, the overall pore size of the support layer is small and the thickness is relatively thick. After the filter membrane is introduced into the support layer, even if there are several large or extra-large pores distributed on the liquid outlet surface of the filter membrane, the internal resistance of the filter membrane will still increase significantly while the external resistance will only decrease slightly, and the filter membrane flux cannot be significantly improved.

[0043] Optionally, the cross-sectional pore area ratio of the support layer is 20-40%, and the SEM average pore diameter of the pores in the cross-section of the support layer is 0.3-1.2 μm.

[0044] By adopting the above technical solution, the filter membrane support layer has a suitable cross-sectional pore area ratio and a suitable average pore diameter, ensuring that the support layer as a whole has a suitable density and mechanical strength. Combined with the filter membrane outlet surface having a suitable pore size, suitable density, and a suitable number of outlet holes and macropores, it is further ensured that the introduction of the support layer results in only a slight increase in the internal resistance of the filter membrane while the external resistance of the filter membrane is greatly improved, and the flux of the filter membrane is significantly enhanced.

[0045] If the pore area ratio of the support layer cross section is <20% and / or the average pore diameter of the support layer is <0.3μm, the pores in the support layer are small and few. The introduction of the support layer will significantly increase the internal resistance of the filter membrane itself, resulting in a low flux of the filter membrane. If the pore area ratio of the support layer cross section is >40% and / or the average pore diameter of the support layer is >1.2μm, the pores in the support layer are large and numerous. This means that the overall mechanical properties of the support layer are relatively insufficient. Under the action of feed liquid pressure, the pore structure of the support layer is likely to deform excessively or even collapse, leading to a significant increase in the internal resistance of the filter membrane while the external resistance only decreases slightly. In other words, the probability that the filter membrane flux cannot be significantly improved is relatively high.

[0046] Understandably, the average pore size and porosity of the support layer can be measured using the following method: first, the cross-section of the PES sterilization membrane can be characterized using an electron microscope to obtain the corresponding SEM image, and then a certain area, such as 1000 μm, can be selected. 2 (20μm x 50μm) or 2500μm 2 (50μm x 50μm), the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to determine the pore diameter of all holes in this area, and then calculate the average value to obtain the average pore diameter of the support layer of this cross section. At the same time, measure the area of ​​all holes in this area, and through calculation, obtain the pore area ratio of the support layer of this cross section.

[0047] Optionally, the average SEM pore size of the support layer gradually increases from the side closer to the first outer surface to the side closer to the second outer surface, and the gradient of the average SEM pore size of the support layer is 0.02~0.12μm / μm.

[0048] By adopting the above technical solution, along the flow direction of the feed liquid, the average pore size of the support layer of the filter membrane of this application gradually increases (the average pore size of the support layer gradually changes with the thickness, and the density gradually decreases without abrupt changes), and the gradient of the average pore size change is appropriate. The average pore size change gradient specifically refers to the change in average pore size per unit thickness; the larger the value, the faster the pore size changes with the thickness; the smaller the value, the smaller the pore size changes with the membrane thickness. The average pore size change gradient is calculated by dividing the difference between the maximum and minimum pore sizes (unit: μm) in a certain region by the thickness between the two positions (the distance between the maximum and minimum pore sizes in that region, unit: μm). Note: If there is a certain thickness at the minimum pore size in that region, the thickness between the two positions refers to the minimum thickness between the maximum and minimum pore sizes.

[0049] If the change value is too small (less than 0.02 μm / μm), it means that the overall pore size of the support layer is relatively small, and the support layer is relatively dense. After introducing a dense support layer with a certain thickness into the filter membrane, the internal resistance of the filter membrane will be significantly higher. Furthermore, if the change value is too small, it may also lead to the overall pore size of the liquid outlet pores on the liquid outlet surface being too small. After introducing the support layer, the decrease in the external resistance of the filter membrane will be small, the internal resistance of the filter membrane will increase significantly while the external resistance will only decrease slightly, and the increase in the filter membrane flux will not be significant. If the change value is too large (greater than 0.12 μm / μm), it means that the overall pore size of the support layer is too large, which also means that the average pore size of the liquid outlet surface (especially the pore size of the large pores) is also relatively large. The overall mechanical properties of the support layer are low. Under the action of high feed liquid pressure, the pore structure of the support layer is likely to deform excessively or even collapse, resulting in a relatively high probability that the internal resistance of the filter membrane will increase significantly while the external resistance will only decrease slightly. That is, the probability that the filter membrane flux cannot be significantly improved is relatively high.

[0050] Optionally, the SEM measurement average aperture increase rate of the support layer near the first outer surface is greater than the SEM measurement average aperture increase rate of the support layer near the second outer surface. The SEM measurement average aperture change gradient of the support layer near the first outer surface is 0.08~0.12μm / μm, and the SEM measurement average aperture change gradient of the support layer near the second outer surface is 0.02~0.05μm / μm.

[0051] By adopting the above technical solution, along the direction of liquid flow, the pore size of the support layer first increases rapidly, then increases slowly. The rapid increase in the pore size of the support layer initially reduces the internal resistance of the filter membrane quickly, thereby minimizing the impact of the support layer on the internal resistance of the filter membrane. After the rapid increase in the pore size of the support layer, the pore size then increases slowly, resulting in a relatively large overall pore size of the filter membrane (especially at the liquid outlet surface), but not excessively large. This ensures that the liquid outlet surface has appropriate pore size, quantity, and density of outlet pores and macropores, significantly reducing the external resistance of the filter membrane. At the same time, it ensures that the porous structure of the support layer (especially near the liquid outlet surface) still possesses high mechanical properties, thereby minimizing the probability of excessive deformation of the porous structure near the liquid outlet surface leading to a significant increase in the internal resistance of the filter membrane.

[0052] In summary, the appropriate "segmented" pore size gradient of the support layer ensures that the support layer as a whole (including the liquid outlet surface) has suitable density and mechanical properties, resulting in only a slight increase in the internal resistance of the filter membrane and a significant decrease in the external resistance, thereby ensuring the high flux of the filter membrane.

[0053] Optionally, the support layer includes support fibers, which are interconnected to form a three-dimensional network structure of the support layer, and the SEM average diameter of the support fibers is 0.1-0.4 μm.

[0054] By adopting the above technical solution, the support layer has support fibers of suitable thickness, further ensuring that the support layer has a high flux. If the support fibers are too fine (less than 0.1 μm), they cannot effectively support the pore structure of the support layer, resulting in relatively insufficient overall mechanical properties of the support layer. Under high feed pressure, the pore structure of the support layer is likely to deform excessively or even collapse, leading to a significant increase in the internal resistance of the filter membrane while the external resistance only decreases slightly. In other words, the probability of the filter membrane flux not being significantly improved is relatively high. If the support fibers are too thick (greater than 0.4 μm), the excessively thick support fibers will create significant resistance to the feed liquid. That is, the introduction of the support layer significantly increases the internal resistance of the filter membrane itself, resulting in a lower overall flux of the filter membrane.

[0055] Optionally, the ratio of the SEM average pore size of the support layer to the SEM average diameter of the support fiber is 2-4 μm / μm.

[0056] By adopting the above technical solution, a suitable ratio is achieved between the average pore size of the support layer and the average diameter of the support fibers. If the ratio is too small, it means that the average pore size of the support layer is relatively small and / or the support fibers are relatively coarse, resulting in a relatively high overall density of the support layer. The introduction of the support layer leads to a significant increase in the internal resistance of the filter membrane, resulting in a low overall flux of the filter membrane. If the ratio is too large, it means that the average pore size of the support layer is relatively large and / or the support fibers are relatively fine. The excessively fine support fibers cannot provide sufficient support for the relatively large pores of the support layer, resulting in insufficient overall mechanical properties of the support layer. Under high feed pressure, the pore structure of the support layer is likely to deform excessively or even collapse, leading to a significant increase in the internal resistance of the filter membrane while the external resistance only decreases slightly. In other words, the probability that the filter membrane flux cannot be significantly improved is relatively high.

[0057] Optionally, the thickness of the separation layer is 10-30 μm, the average SEM pore size of the pores in the cross-section of the separation layer is 0.15-0.95 μm, and the pore area ratio of the cross-section of the separation layer is 15-25%.

[0058] By adopting the above technical solution, the separation layer has a suitable thickness (10-30μm), a suitable average pore size, and a suitable pore area ratio (15-25%), thereby ensuring that the separation layer of the filter membrane has a suitable three-dimensional network structure and the filter membrane as a whole has a relatively suitable internal resistance, thereby further ensuring the filter membrane's retention performance and flux.

[0059] If the separation layer is too thick (thickness greater than 30 μm) and / or the average pore size of the separation layer is too small (less than 0.15 μm), the separation layer with small pores and high thickness will certainly significantly improve the filtration performance of the filter membrane for bacteria, but at the same time, it will inevitably increase the overall internal resistance of the filter membrane, leading to a decrease in the filter membrane flux. If the separation layer is too thin (thickness less than 10 μm) and / or the average pore size of the separation layer is too large (greater than 0.95 μm), the filtration performance of the filter membrane for bacteria may be unsatisfactory. If the cross-sectional pore area ratio of the separation layer is too low (less than 15%), it means that the overall density of the separation layer is relatively high, the internal resistance of the filter membrane is relatively high, and it is easy to cause a decrease in the flux of the filter membrane. If the cross-sectional pore area ratio of the separation layer is too high (greater than 25%), the relatively high pore area ratio of the separation layer also means that the overall density of the separation layer is relatively low, that is, the overall three-dimensional network structure of the separation layer is relatively loose. Although this means that the internal resistance of the filter membrane is relatively low, it may lead to a lower bacterial filtration performance. Since the filter membrane of this application is used as a sterilization and bacteriostatic filter membrane, its bacterial filtration performance must be guaranteed. Therefore, the cross-sectional pore area ratio of the separation layer cannot be too high.

[0060] Optionally, the pore area ratio of the separation layer cross section is less than that of the support layer cross section, and the difference between the pore area ratio of the support layer cross section and the pore area ratio of the separation layer cross section is 5-15%.

[0061] By adopting the above technical solution, a suitable difference (5-15%) exists between the cross-sectional pore area ratio of the support layer and the cross-sectional pore area ratio of the separation layer. This suitable difference allows for a suitable flow rate difference between the feed liquid and the separation layer, resulting in a relatively high flow rate of the feed liquid in the support layer. This promotes the flow of the feed liquid from the separation layer to the support layer (the feed liquid in the support layer exerts a drag force on the feed liquid in the separation layer), thereby further increasing the flux of the filter membrane. If the difference between the two is small, the flow rate difference between the support layer and the separation layer is small, reducing the drag force of the feed liquid in the support layer on the feed liquid in the separation layer, thus reducing the flux of the filter membrane. If the difference between the pore area ratio of the support layer and the pore area ratio of the separation layer is large, the instantaneous flow rate of the feed liquid in the support layer (especially the liquid outlet surface) is large. The amount of feed liquid that flows into the separation layer instantaneously cannot meet the timely outflow, easily causing blockage of the flow channels inside the membrane, thereby reducing the flux of the filter membrane.

[0062] Optionally, one side of the pre-filter layer is the first outer surface, the thickness of the pre-filter layer is 60-90μm, the SEM average pore size of the pre-filter layer is 0.6-1.5μm, and the pore area ratio of the cross section of the pre-filter layer is 25%-45%.

[0063] By adopting the above technical solution and setting a pre-filtration layer, compared with the separation layer, the pre-filtration layer has a relatively large thickness (60-90μm), relatively large pores (average pore diameter greater than 0.4μm), and a relatively large number of pores (pore area ratio greater than 25%). This can effectively filter out large particles in the feed liquid, reduce the probability of large particles directly clogging the separation layer, and thus extend the service life of the PES sterilization membrane.

[0064] Of course, the average pore size and pore area ratio of the pre-filter layer are not necessarily better the larger they are. This is because if the average pore size of the pre-filter layer is too large (average pore size greater than 0.9μm) and the number of pores is too large (pore area ratio greater than 45%), it means that the pre-filter layer is relatively "loose". During filtration, the pressure of the liquid directly acts on the pre-filter layer. An overly "loose" pre-filter layer is prone to deformation and compression due to the pressure of the liquid, resulting in a decrease in the overall flux and dirt holding capacity of the sterilization membrane.

[0065] Secondly, this application provides a method for preparing an asymmetric PES filter membrane, employing the following technical solution:

[0066] S1. The casting solution is prepared and cast onto a carrier to form a liquid film. The casting solution comprises at least the following raw materials in parts by weight: 20-45 parts of polyethersulfone resin, 55-80 parts of solvent, and 10-25 parts of pore-forming agent; the casting solution temperature is 40-60℃; and the solid content of polyethersulfone resin in the casting solution is 15-35%.

[0067] S2. Pretreatment: The carrier loaded with the liquid film is placed in a pretreatment bath for pretreatment for 2-8 seconds to obtain a pretreated membrane. The pretreatment bath includes a good pretreatment solvent and a non-pretreatment solvent, and the concentration of the good pretreatment solvent in the pretreatment bath is 80-95 wt%.

[0068] S3. Reprocessing: The carrier loaded with the pretreated membrane is placed in a reprocessing bath for secondary treatment for 3-10 seconds to obtain a retreated membrane. The reprocessing bath includes a good reprocessing solvent and a non-reprocessing solvent, and the concentration of the good reprocessing solvent in the reprocessing bath is 50-60 wt%.

[0069] S4. Curing: The carrier loaded with the reprocessed membrane is immersed in a coagulation bath for phase separation and curing. After phase separation, a raw membrane is obtained. The coagulation bath includes a good phase separation solvent and a phase separation non-solvent. The concentration of the phase separation non-solvent in the coagulation bath is 70~95wt%, and the phase separation curing time is 40-150s.

[0070] S5. Membrane formation: The raw membrane is washed with pure water and then dried to obtain the PES filter membrane.

[0071] By adopting the above technical solution, the first step in preparing the PES sterilization membrane is the preparation of the casting solution. In this application, by controlling the casting solution to have a suitable solid content (the solid content refers to the mass ratio of polyethersulfone in the casting solution) and by controlling the temperature of the casting solution, the casting solution has a suitable viscosity and fluidity, which facilitates the subsequent phase separation and curing steps.

[0072] The second step involves pretreatment of the air side of the liquid membrane in a pretreatment bath, forming the support layer required for the PES filter membrane of this application. The pretreatment bath contains a high content of good pretreatment solvent, which dilutes the air side of the liquid membrane, appropriately reducing the solid content in the casting solution and thus facilitating the formation of a support layer with a larger average pore size. The pretreatment time is 2-8 seconds. This suitable pretreatment time allows the casting solution sufficient time to form polymer-rich and solvent-rich phases of appropriate sizes, thus fostering a tendency for the second outer surface to initially form macropores. It is understandable that, due to the high content of good pretreatment solvent in the pretreatment bath, the liquid membrane will undergo phase separation but will not experience excessive solidification (or even any solidification at all).

[0073] The third step involves a reprocessing bath to further treat the air side of the pretreated membrane. This reprocessing bath contains a certain concentration of a good reprocessing solvent and a non-reprocessing solvent. After pretreatment, the polymer-rich phase of the pretreated membrane contains relatively little solvent. When the pretreated membrane is immersed in the reprocessing bath, the polymer-rich phase begins to solidify and form the large pores required for the liquid outlet surface of the PES filter membrane in this application. Furthermore, since the liquid membrane has already undergone pretreatment, the air side of the liquid membrane has been initially diluted, meaning the solid content on the air side of the pretreated membrane is relatively low. Therefore, in the reprocessing bath, on the one hand, under the action of the non-reprocessing solvent, the porous bulk near the air side of the pretreated membrane undergoes initial phase separation, forming relatively large pores for liquid outlet. On the other hand, the good reprocessing solvent in the reprocessing bath further dilutes the liquid outlet surface of the pretreated membrane, further reducing the solid content. In other words, through the synergistic effect of pretreatment, reprocessing, and a suitable solid content, the liquid membrane forms the support layer with a non-uniform pore structure required in this application. Furthermore, by controlling the pretreatment and retreatment times, and combining this with the appropriate viscosity of the casting solution, the thickness of the support layer can be further controlled. The longer the pretreatment and retreatment times, the thicker the support layer.

[0074] The fourth step is curing, specifically, immersing the carrier loaded with the reprocessing membrane in a coagulation bath for phase separation and curing. After curing, a green membrane is obtained. Since the support layer has already formed a preliminary support layer with relatively large and uneven pore sizes, the coagulation bath can quickly penetrate from the air side of the reprocessing membrane into its interior. Under the action of the coagulation bath, the support layer is completely cured. Simultaneously, the non-solvent content in the coagulation bath is relatively high, resulting in a relatively fast phase separation rate inside the reprocessing membrane, which is beneficial for forming a separation layer with a smaller pore size. Furthermore, due to the smaller pore size of the separation layer, after the coagulation bath penetrates into the separation layer, it encounters significant resistance, reducing the coagulation bath penetration rate and slowing down the phase separation rate. This forms a pre-filtration layer on the carrier side, thus forming the desired membrane structure (viewed along the membrane thickness direction, the pore size of the filter membrane first decreases and then increases).

[0075] The fourth step is the film formation step, in which the raw membrane is washed with pure water and then dried to obtain the PES filter membrane.

[0076] Optionally, there is an air section between step S2 and step S3, and the pretreatment membrane stays in the air section for 1-10 seconds.

[0077] By adopting the above technical solution, the air section allows the pretreatment bath to permeate from the second outer surface of the liquid membrane to the first outer surface (carrier side) near the liquid membrane without any additional pretreatment bath being added to the liquid membrane. On the one hand, this avoids excessive dilution of the casting solution near the second outer surface of the liquid membrane, thus preventing the formation of too many and too large pores. On the other hand, the less pretreatment bath is present near the carrier side of the liquid membrane, the smaller the size of the polymer-rich phase formed. That is, the closer the support layer is to the first outer surface of the filter membrane, the smaller the pore size of the support layer, thereby ensuring that the support layer of the filter membrane of this application has a suitable pore size gradient.

[0078] Optionally, in step S2, the temperature on the carrier side is 1-10°C lower than the pretreatment bath temperature.

[0079] By adopting the above scheme, the temperature on the carrier side is relatively low, and the viscosity of the casting liquid near the carrier side is relatively high. When the pretreatment bath penetrates from the second outer surface of the liquid film to the first outer surface (carrier side) near the liquid film to a certain thickness, the pretreatment bath solvent is difficult to continue to penetrate, which is more conducive to forming the support layer with a certain thickness but not too thick as required by this application.

[0080] Optionally, the solvent, pretreatment solvent, retreatment solvent, and phase separation solvent are all one or a mixture of at least two of the following: butyl lactate, dimethyl sulfoxide, dimethylformamide, caprolactam, methyl acetate, ethyl acetate, N-ethylpyrrolidone, dimethylacetamide, and N-methylpyrrolidone.

[0081] The pretreatment non-solvent, the retreatment non-solvent, and the phase separation non-solvent are all water;

[0082] The pore-forming agent is one or a mixture of at least two of polyvinyl alcohol, polyethylene glycol, polyethyleneimine, and polyvinylpyrrolidone.

[0083] Thirdly, this application provides a filtering component, which adopts the following technical solution:

[0084] A filtration assembly includes a housing, within which 1-3 layers of asymmetric PES filter membranes are disposed, preferably 2 layers. Preferably, the 2 layers of asymmetric PES filter membranes are specifically divided into an upstream filter membrane and a downstream filter membrane, and the 2 layers of asymmetric PES filter membranes are stacked together. For example, two 0.45μm-level antibacterial membranes are stacked together; or, for another example, the upstream filter membrane is a 0.45μm-level antibacterial membrane, and the downstream filter membrane is a 0.22μm-level antibacterial membrane.

[0085] This application provides the following beneficial effects: the PES filter membrane, the method for preparing the PES filter membrane, and a filtration assembly provided in this application, wherein the prepared PES sterilization membrane has high bacterial filtration performance and high dirt-holding capacity (high loading capacity). Furthermore, in actual use, the filter membrane also has a high flux. The preparation method provided by this invention can conveniently, quickly, and effectively prepare the above-mentioned sterilization membrane. Attached Figure Description

[0086] Figure 1 This is a schematic diagram of the second outer surface of the PES filter membrane prepared in Example 1 using a scanning electron microscope (SEM), with a magnification of 2000×.

[0087] Figure 2 This is a schematic diagram of the second outer surface of the PES filter membrane prepared in Example 1 using a scanning electron microscope (SEM), with a magnification of 5000×.

[0088] Figure 3 This is a schematic diagram of the cross-section of the PES filter membrane prepared in Example 1 using a scanning electron microscope (SEM), with a magnification of 300×.

[0089] Figure 4 This is a schematic diagram of the second outer surface of the PES filter membrane prepared in Example 4 using a scanning electron microscope (SEM), with a magnification of 1000×.

[0090] Figure 5 This is a schematic diagram of the apparatus for PES filter membrane flux testing in this application. Detailed Implementation Example 1

[0091] This application discloses an asymmetric PES filter membrane, which is prepared using the following process steps:

[0092] S1. The casting solution is prepared and cast onto a carrier to form a liquid film. The casting solution includes the following raw materials in parts by weight: 32 parts polyethersulfone resin, 68 parts solvent and 18 parts pore-forming agent; the casting solution temperature is 50℃; the solvent is butyl lactate and the pore-forming agent is polyvinyl alcohol.

[0093] S2. Pretreatment: The carrier loaded with the liquid film is placed in a pretreatment bath for pretreatment for 5 seconds to obtain a pretreated membrane. The pretreatment bath includes a good pretreatment solvent and a non-pretreatment solvent. The concentration of the good pretreatment solvent in the pretreatment bath is 85 wt%. The good pretreatment solvent is butyl lactate, and the non-pretreatment solvent is water. The temperature on the carrier side is 5°C lower than the temperature of the pretreatment bath.

[0094] After pretreatment, the pretreated membrane remains in the air section for 5 seconds.

[0095] S3. Reprocessing: The carrier loaded with the pretreated membrane is placed in a reprocessing bath for secondary treatment. The reprocessing time is 6.5s to obtain a retreated membrane. The reprocessing bath includes a good reprocessing solvent and a non-reprocessing solvent. The concentration of the good reprocessing solvent in the reprocessing bath is 55wt%. The good reprocessing solvent is butyl lactate, and the non-reprocessing solvent is water.

[0096] S4. Curing: The carrier loaded with the reprocessed membrane is immersed in a coagulation bath for phase separation and curing. After phase separation and curing, a green film is obtained. The coagulation bath includes a good phase separation solvent and a non-phase separation solvent. The concentration of the non-phase separation solvent in the coagulation bath is 80 wt%, and the phase separation and curing time is 95 s. The good phase separation solvent is butyl lactate, and the non-phase separation solvent is water.

[0097] S5. Membrane formation: The raw membrane is washed in pure water and then dried to obtain the PES filter membrane.

[0098] Examples 2-7

[0099] The difference between Examples 2-7 and Example 1 lies in the different casting solution formulations and process parameters, as detailed in Tables 1 and 2.

[0100] It should be noted that in Example 4, the pretreatment membrane did not stay in the air section between steps S2 and S3; in Example 5, the pretreatment membrane stayed in the air section for a longer period of time (greater than 10 seconds) between steps S2 (pretreatment) and S3 (retreatment). Comparative Example 1

[0101] The difference between Comparative Example 1 and Example 1 is that the casting solution formulation and various process parameters are different, as detailed in Tables 1 and 2. It should be noted that Comparative Example 1 does not include a pretreatment step, and the carrier loaded with the liquid film is directly immersed in the reprocessing bath for phase separation and solidification. Comparative Example 2

[0102] The difference between Comparative Example 1 and Example 1 lies in the different casting solution formulations and process parameters, as detailed in Tables 1 and 2. It should be noted that in step S2 of Comparative Example 2, the content of good pretreatment solvent in the pretreatment bath is higher (above 90 wt%), while in step S3, the content of good retreatment solvent in the retreatment bath is lower (below 50 wt%).

[0103] Application Example 1

[0104] A filter assembly is disclosed in Chinese Utility Model Patent Document CN202155092U, which is a needle filter. The needle filter contains a PES filter membrane, wherein the PES filter membrane is the filter membrane prepared in Example 1 of this application.

[0105] Application Example 2

[0106] The difference between Application Example 2 and Application Example 1 is that the PES filter membrane placed inside the needle filter is the filter membrane prepared in Example 3 plus the filter membrane prepared in Example 1. The two filter membranes are used in a stacked manner, with the filter membrane prepared in Example 3 on top and the filter membrane prepared in Example 1 on the bottom.

[0107] Comparative Application Example 1

[0108] The difference between Comparative Example 1 and Comparative Example 2 is that the PES filter membrane placed inside the needle filter is the filter membrane prepared in Comparative Example 1.

[0109] Comparative Application Example 2

[0110] The difference between Application Example 2 and Application Example 1 is that the PES filter membrane placed inside the needle filter is the filter membrane prepared in Comparative Example 2 + the filter membrane prepared in Comparative Example 1. The two filter membranes are used in a stacked manner, with the filter membrane prepared in Comparative Example 2 on top and the filter membrane prepared in Comparative Example 1 on the bottom.

[0111] Table 1. Casting solution formulations for each embodiment and comparative example.

[0112] polyethersulfone resin mass fraction Solvent mass parts Pore-forming agent mass fraction Casting solution temperature / ℃ Solid content / % Example 1 30 66 18 50 26.32% Example 2 45 75 20 40 32.14% Example 3 20 75 15 60 18.18% Example 4 22 55 22 42 22.22% Example 5 38 68 24 48 29.23% Example 6 23 53 20 58 23.96% Example 7 20 60 25 46 19.04% Comparative Example 1 32 68 20 54 26.67% Comparative Example 2 33 74 16 56 26.83%

[0113] Table 2. Process parameters for each embodiment and comparative example.

[0114]

[0115] Performance testing and data

[0116] The detection methods are as follows:

[0117] PMI average pore size: The PES sterilization membranes prepared in each example and comparative example were used as samples, and the PMI average pore size of each sample was tested using a CFP-1J00AEX PMI pore size tester.

[0118] LRV: PES filter membranes prepared in each example and comparative example were used as samples for bacterial retention challenge tests. The detection method was based on the guidance document TR26 issued by the PDA. During the test, Pseudomonas degenerativeae (ATCC 19146) with a bacterial diameter of 0.3-0.4 μm was used as the retained bacteria. The bacterial retention test was performed on the samples according to the standard ASTM F838-2015ae1 to test the LRV value of the filter membrane.

[0119] Flux testing (testing equipment such as) Figure 5 )

[0120] ①: Preparation of membrane module; The filter membrane to be tested is cut into a square membrane sheet of 1.5cm*0.5cm, and the non-woven fabric is cut into a square sheet of 1.5cm*0.5cm. The filter membrane and the non-woven fabric are stacked to form a membrane module.

[0121] ②: Test solution (water) adjustment; Adjust the temperature of the test solution (water) to 20℃;

[0122] ③: Test solution injection; close all valves and inject the test solution (water) into the pressure vessel;

[0123] ④: Venting; Install the membrane module on the pressure filter bracket, apply low pressure to the pressure vessel, open valve 2 and vent valve 2 to purge air from the piping. Confirm that all air has been expelled by the start of test solution discharge from vent valve 2. After venting, close vent valve 2 and the valve.

[0124] ⑤: Pressure adjustment; Adjust the pressure to 0.03 MPa using an air pressure regulator;

[0125] ⑥: Test; Open the valve, place the measuring cylinder on the outlet side of the pressure filter bracket, and measure the amount of test liquid filtered by the membrane module in one minute.

[0126] The morphological parameters of the PES antibacterial membranes prepared in each embodiment and comparative example are detailed in Tables 3, 4 and 5, and the performance parameters are detailed in Table 6.

[0127] Table 3. Morphological parameters of the liquid outlet surface of the PES filter membranes prepared in each embodiment and comparative example.

[0128] <![CDATA[Average pore diameter D2 of liquid outlet hole / μm]]> Surface porosity coefficient I / % <![CDATA[Macropore density ρ 大孔 > Pore ​​area ratio of liquid outlet / % Liquid outlet density ρ <![CDATA[Extra-large pore density ρ 特大孔 > Example 1 1.17 19.8% 133 12.4 672 3 Example 2 0.43 21.1% 188 4.1 892 14 Example 3 1.92 17.6% 82 17.8 465 1 Example 4 1.45 13.6% 156 28 1145 4 Example 5 0.68 20.6% 192 7.3 934 27 Example 6 1.28 25.4% 161 15.9 635 2 Example 7 1.73 29.2% 152 19.7 521 1 Comparative Example 1 0.54 2.0% 20 6.6 988 / Comparative Example 2 2.10 30.4% 143 30.1 471 2

[0129] Remark:

[0130] Macropore density ρ 大孔 1. Liquid outlet pore density ρ, Extra-large pore density ρ 特大孔 The units are all: cells / 10000μm 2 .

[0131] Table 4. Morphological parameters of the support layer of the PES filter membranes prepared in each embodiment and comparative example.

[0132] Support layer thickness h / μm h / H <![CDATA[D2 / h]]> Support layer cross-sectional void area ratio / % Support layer SEM average pore size / μm Gradient of average pore size variation in support layer / μm / μm Average diameter of supporting fibers / μm The ratio of the average pore size of the support layer to the average diameter of the support fibers Example 1 14.8 0.136 0.079 31.2 0.79 0.061 0.24 3.29 Example 2 10.2 0.123 0.042 21.3 0.33 0.025 0.14 2.36 Example 3 18.8 0.138 0.102 39.6 1.16 0.059 0.37 3.14 Example 4 12.9 0.112 0.112 34.9 0.91 0.086 0.29 3.14 Example 5 11.3 0.120 0.060 25.8 0.67 0.039 0.18 3.72 Example 6 8.4 0.079 0.152 33.5 0.86 0.115 0.27 3.19 Example 7 19.9 0.177 0.087 38.1 1.09 0.054 0.34 3.21 Comparative Example 1 13.8 0.142 0.039 22.5 0.42 0.025 0.19 2.21 Comparative Example 2 17.9 0.132 0.117 41.8 1.44 0.071 0.42 3.43

[0133] Table 5. Morphological parameters of the pre-filtration layer and separation layer of the PES filter membranes prepared in each embodiment and comparative example.

[0134] Separation layer thickness / μm Average pore size of the separation layer / μm Pore ​​area ratio of the separation layer section / % Difference in pore area ratio between support layer and separation layer / % Pre-filter layer thickness / μm SEM average pore size of pre-filter layer (μm) Pore ​​area ratio of pre-filter layer cross section / % Example 1 19.3 0.27 19.4 11.8 74.5 0.77 35.9 Example 2 11.8 0.18 15.9 5.4 61.2 0.52 27.3 Example 3 29.4 0.81 24.7 14.9 88.4 1.45 44.5 Example 4 22.1 0.34 23.5 11.4 80.4 0.88 39.4 Example 5 14.5 0.24 17.2 8.6 68.1 0.59 31.1 Example 6 20.8 0.31 22.4 11.1 77.3 0.83 37.6 Example 7 27.1 0.65 23.4 14.7 65.5 1.33 42.5 Comparative Example 1 11.3 0.19 16.1 6.4 72.4 0.78 36.1 Comparative Example 2 25.6 0.83 26.5 15.3 91.8 1.74 45.2

[0135] Table 6 Performance parameters of PES filter membranes prepared in each embodiment and comparative example

[0136] PMI average pore size LRV Flux / ml Film thickness H / μm Example 1 0.22 ＞7 10.4 108.6 Example 2 0.15 ＞8 7.9 83.2 Example 3 0.57 ＞4 19.6 136.6 Example 4 0.28 ＞7 8.5 115.4 Example 5 0.18 ＞8 6.6 93.9 Example 6 0.25 ＞7 7.3 106.5 Example 7 0.43 ＞5 9.8 112.5 Comparative Example 1 0.16 ＞7 3.6 97.5 Comparative Example 2 0.60 ＞4 9.1 135.3

[0137] Remark:

[0138] Flux specifically refers to the amount of test liquid (water) that passes through a membrane module (PES filter membrane and non-woven fabric laminated) with dimensions of 1.5cm*0.5cm within 1 minute under conditions of pressure of 0.03Mpa and temperature of 20℃.

[0139] Table 6 Performance parameters of PES filter membranes prepared in each application example and comparative application example

[0140] LRV Flux / ml Application Example 1 ＞7 11.2 Application Example 2 ＞10 7.1 Comparative Application Example 1 ＞7 4.2 Comparative Application Example 2 ＞10 1.9

[0141] in conclusion

[0142] The PES filter membrane in this application is not limited to single-layer use. In actual use, a single-layer PES filter membrane can be selected for use, or two or more layers of PES filter membranes can be stacked together to obtain the desired bacterial filtration effect, depending on the actual needs. For example, although the PES filter membrane of Example 3 has a high flux, its average pore size (PMI) is relatively high (0.57 μm), and its bacterial retention capacity is relatively poor (LRV < 7). Therefore, in actual use, PES membranes can be stacked together to maintain a high bacterial retention capacity. For example, two layers of PES filter membranes from Example 3 can be stacked together, or, for example, a combination of the PES filter membrane from Example 3 and the PES filter membrane from Example 1 can be stacked together.

[0143] By comparing Example 2 and Comparative Example 1, it is easy to see that the separation layer thickness and overall membrane thickness of the PES filter membrane in Comparative Example 1 are both smaller than those in Example 2. Furthermore, the average pore size of the PMI, the average pore size of the effluent pores, and the average pore size of the separation layer of the PES filter membrane in Comparative Example 1 are all larger than those in Example 2. The expected effect is that, in actual use, the flux of the filter membrane in Comparative Example 1 is higher than that of the filter membrane in Example 2. However, in actual use, the flux of the filter membrane in Comparative Example 1 is significantly lower than that of the filter membrane in Example 2. This may be because the pores on the pore surface of the filter membrane in Comparative Example 1 are too uniform, that is, the pore surface does not contain large pore structures, resulting in a high density of the pore surface. After the introduction of the support layer, the internal resistance of the filter membrane increases significantly, while the external resistance of the filter membrane decreases only slightly. Furthermore, under the action of the feed liquid pressure, the pore surface of the filter membrane prepared in Comparative Example 1 is pressed against the nonwoven fabric, and the nonwoven fabric blocks the pores of the filter membrane in Comparative Example 1, which will cause a significant increase in the external resistance of the filter membrane. Therefore, the flux of the filter membrane in Comparative Example 1 is much lower than that of the filter membrane in Example 2.

[0144] By comparing Example 3 and Comparative Example 2, it is easy to see that the separation layer thickness and overall membrane thickness of the PES filter membrane in Comparative Example 2 are both smaller than those in Example 3. Furthermore, the average pore size (PMI), average pore size (outlet pores), and average pore size (separation layer) of the PES filter membrane in Comparative Example 1 are all larger than those in Example 1. Moreover, the filter membrane in Comparative Example 2 contains a large number of macroporous structures (the surface porosity of this filter membrane is much higher than that of Example 3). The expected effect is that the flux of the filter membrane in Comparative Example 2 is higher than that of the filter membrane in Example 1. However, in actual use, the flux of the filter membrane in Comparative Example 2 is much lower than that of the filter membrane in Example 3. This may be because the outlet pores on the outlet surface of the filter membrane in Comparative Example 2 are too uneven, i.e., the outlet surface does not contain many macroporous structures. Admittedly, a large number of macroporous structures on the outlet surface indicates a lower density of the filter membrane's outlet surface. Low density will inevitably cause a loss of mechanical properties in the porous matrix near the outlet surface. If the loss of mechanical properties is too great, the degree of deformation of the filter membrane will be greater during actual use. If the filter membrane undergoes excessive deformation, on the one hand, the pores on the liquid outlet surface of the filter membrane will collapse and become blocked; on the other hand, the filter membrane and the nonwoven fabric will become even more tightly pressed together, and the nonwoven fabric will block the liquid outlet pores of the filter membrane in Comparative Example 1. Under the combined effect of these two factors, the internal resistance of the filter membrane will actually increase significantly. Therefore, the flux of the filter membrane in Comparative Example 2 is much lower than that of the filter membrane in Example 3.

[0145] By comparing Examples 1 and 4, it can be found that the average pore size of the liquid outlet pores in Example 4 is higher than that in Example 1, and the pore area ratio and density of the liquid outlet pores in Example 4 are much higher than those in Example 1. The expected effect is that the density of the liquid outlet surface in Example 4 is much lower than that in Example 1. In actual use, the flux of the PES filter membrane in Example 4 is higher than that in Example 1. However, in actual use, the flux of the PES filter membrane in Example 4 is lower than that in Example 1. This may be because the density of the PES filter membrane at the liquid outlet surface in Example 4 is relatively low. Although this means that the introduction of the support layer results in a smaller increase in the internal resistance of the filter membrane itself, the lower density at the liquid outlet surface also means that the mechanical properties of the porous body near the liquid outlet surface are relatively low. Under the action of the feed liquid pressure, it is easy to cause excessive deformation of some pores at the liquid outlet surface of the filter membrane, or even the collapse of some pores. This will reduce the reduction in the external resistance of the filter membrane and increase the internal resistance of the filter membrane, thus limiting the increase in the flux of the filter membrane. As a result, in actual use, the flux of the PES filter membrane in Example 4 is higher than that in Example 1.

[0146] Comparing Examples 2 and 5, it can be found that the average pore size of the PMI, the average pore size of the separation layer, the average pore size of the liquid outlet pores, and the macropore density of the liquid outlet surface of the PES filter membrane in Example 5 are all greater than those in Example 2. Furthermore, the number of extra-large pores on the liquid outlet surface of the PES filter membrane in Example 5 is also higher than that in Example 2. The expected effect is that the density of the liquid outlet surface of the PES filter membrane in Example 5 is much lower than that in Example 2. After the introduction of the support layer, the increase in internal resistance of the PES filter membrane in Example 5 is less than that in Example 2, while the decrease in external resistance is greater than that in Example 2. The actual flux of the PES filter membrane in Example 5 is lower than that in Example 2. However, in actual use, the actual flux of the PES filter membrane in Example 2 is higher than that in Example 5. This may be because the number of extra-large pores on the liquid outlet surface of the filter membrane in Example 5 is too high (greater than 20 pores / 10000 μm). 2 The PES filter membrane in Example 5 has a relatively large number of areas with low overall mechanical properties. Under the pressure of the feed liquid, the porous body near each extra-large hole is more likely to undergo excessive deformation or even collapse. Once it undergoes excessive deformation or collapses, the internal resistance of the filter membrane will increase significantly, and the reduction in the external resistance of the filter membrane will decrease. As a result, the actual flux of the PES filter membrane in Example 5 is lower than that in Example 2.

[0147] By comparing Examples 1 and 6, it can be found that the thickness of the support layer of the filter membrane in Example 6 is smaller than that in Example 1, and the average pore size of the outlet pores of the filter membrane in Example 6 is larger than that in Example 1. The expected effect is that after the introduction of the support layer, the increase in internal resistance of the filter membrane in Example 6 is lower than that in Example 1, while the decrease in external resistance is higher than that in Example 1, and the actual flux of the filter membrane in Example 6 is higher than that in Example 1. However, in actual use, the actual flux of the PES filter membrane in Example 1 is higher than that in Example 6. This may be because the thickness of the support layer in Example 6 is too thin, and its overall mechanical properties are relatively insufficient. Under the action of feed pressure, excessive deformation is likely to occur in the area near the macropore structure and the extra-large pore structure of the filter membrane, leading to a relatively high probability that its internal resistance will increase significantly while its external resistance will only decrease slightly. This results in a limited increase in the flux of the filter membrane in Example 6, thus causing the actual flux of the filter membrane in Example 6 to be lower than that in Example 1 in actual use.

[0148] By comparing Application Examples 1-2 and Comparative Application Examples 1-2, it can be found that the filter membrane prepared in this application is particularly suitable for stacking in membrane filters. This is likely because, in actual use, the solid portion of the inlet surface of the downstream filter membrane inevitably blocks the pores of the outlet surface of the upstream filter membrane. For ordinary filter membranes, once the pores of the outlet surface of the upstream filter membrane are blocked, the external resistance of the filter membrane will undoubtedly increase, leading to a significant decrease in the flux. Furthermore, it is also unavoidable that the pores of the outlet surface of the downstream filter membrane will be blocked by the internal support structure of the membrane filter. Once the pores of the outlet surface of the downstream filter membrane are blocked, the external resistance of the filter membrane will undoubtedly increase. Under the combined effect of these two factors, the overall flux within the membrane filter will be significantly reduced. However, using the filter membrane of this application, even if the outlet pores of the upstream and downstream filter membranes are partially blocked, both still have high flux, thus ensuring that the overall membrane filter has a high flux.

[0149] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. An asymmetric PES filter membrane, comprising a porous body having non-directional tortuous pathways within the porous body, one side of the porous body being a first outer surface, and the other side of the porous body being a second outer surface, characterized in that: The porous body includes a pre-filtration layer, a separation layer for retaining bacteria, and a support layer. One side of the pre-filtration layer is a first outer surface, and one side of the support layer is a second outer surface. The pre-filtration layer, the separation layer, and the support layer are connected by continuous fibers. The average pore size measured by SEM of the support layer is greater than that measured by SEM of the separation layer. The average pore size of the filter membrane is 0.15-0.6 μm. The second outer surface has a plurality of liquid outlet holes, the SEM average pore diameter D2 of which is 0.4-2.0 μm; the second outer surface also has a plurality of macropores, the pore diameter D of which is... 大孔 Not less than 1.5D2; The surface porosity coefficient I of the second outer surface is 13%-30%, and the surface porosity coefficient I is calculated by the following formula: I=(ρ 大孔 / ρ)×100%, where ρ 大孔 ρ represents the density of macropores on the second outer surface; ρ represents the density of effluent pores on the second outer surface, in units of pores / 10000μm. 2 ; The density ρ of the large pores on the second outer surface 大孔 80-200 per 10000μm 2 .

2. The asymmetric PES filter membrane according to claim 1, characterized in that: The pore area ratio of the liquid outlet holes is 4-18%, and the density ρ of the liquid outlet holes on the second outer surface is 450-950 holes / 10000μm. 2 .

3. The asymmetric PES filter membrane according to claim 1, characterized in that: The second outer surface has a plurality of extra-large holes, wherein the diameter D of the extra-large holes is... 特大孔 The pore density ρ of the extra-large pore is not less than 3D2. 特大孔 No more than 20 per 10000μm 2 .

4. The asymmetric PES filter membrane according to claim 1, characterized in that: The thickness h of the support layer is 10-20 μm, and the ratio of the thickness h of the support layer to the thickness H of the porous body is 0.1-0.

18.

5. The asymmetric PES filter membrane according to claim 4, characterized in that: The ratio of the SEM average pore size D2 of the liquid outlet to the thickness h of the support layer is 0.04-0.12 μm / μm.

6. The asymmetric PES filter membrane according to claim 1, characterized in that: The cross-sectional pore area ratio of the support layer is 20-40%, and the average SEM pore size of the support layer is 0.3-1.2 μm.

7. The asymmetric PES filter membrane according to claim 1, characterized in that: The average pore size of the support layer under SEM measurements gradually increases from the side closer to the first outer surface to the side closer to the second outer surface, and the gradient of the average pore size of the support layer under SEM measurements is 0.02~0.12μm / μm.

8. The asymmetric PES filter membrane according to claim 1, characterized in that: The rate of increase of the average pore size measured by SEM on the side of the support layer near the first outer surface is greater than the rate of increase of the average pore size measured by SEM on the side of the support layer near the second outer surface. The gradient of the average pore size measured by SEM on the side of the support layer near the first outer surface is 0.08~0.12μm / μm, and the gradient of the average pore size measured by SEM on the side of the support layer near the second outer surface is 0.02~0.05μm / μm.

9. The asymmetric PES filter membrane according to claim 1, characterized in that: The support layer includes support fibers, which are interconnected to form a three-dimensional network structure of the support layer. The SEM average diameter of the support fibers is 0.1-0.4 μm.

10. An asymmetric PES filter membrane according to claim 8, characterized in that: The ratio of the average SEM pore size of the support layer to the average SEM diameter of the support fiber is 2-4 μm / μm.

11. An asymmetric PES filter membrane according to claim 1, characterized in that: The thickness of the separation layer is 10-30 μm, the average SEM pore size of the pores in the cross-section of the separation layer is 0.15-0.95 μm, and the pore area ratio of the cross-section of the separation layer is 15-25%.

12. The asymmetric PES filter membrane according to claim 11, characterized in that: The pore area ratio of the separation layer cross section is less than that of the support layer cross section, and the difference between the pore area ratio of the support layer cross section and the pore area ratio of the separation layer cross section is 5-15%.

13. The asymmetric PES filter membrane according to claim 1, characterized in that: The surface of one side of the pre-filter layer is the first outer surface. The thickness of the pre-filter layer is 60-90 μm, the average SEM pore size of the pre-filter layer is 0.6-1.5 μm, and the pore area ratio of the cross-section of the pre-filter layer is 25%-45%.

14. The preparation process of an asymmetric PES filter membrane according to any one of claims 1-13, characterized in that: The process includes the following steps: S1. The casting solution is prepared and cast onto a carrier to form a liquid film. The casting solution includes at least the following raw materials in parts by weight: 20-45 parts of polyethersulfone resin, 55-80 parts of solvent and 10-25 parts of pore-forming agent; the casting solution temperature is 40-60℃. S2. Pretreatment: The carrier loaded with the liquid film is placed in a pretreatment bath for pretreatment for 2-8 seconds to obtain a pretreated membrane. The pretreatment bath includes a good pretreatment solvent and a non-pretreatment solvent, and the concentration of the good pretreatment solvent in the pretreatment bath is 80-95 wt%. S3. Reprocessing: The carrier loaded with the pretreated membrane is placed in a reprocessing bath for secondary treatment for 3-10 seconds to obtain a retreated membrane. The reprocessing bath includes a good reprocessing solvent and a non-reprocessing solvent, and the concentration of the good reprocessing solvent in the reprocessing bath is 50-60 wt%. S4. Curing: The carrier loaded with the reprocessed membrane is immersed in a coagulation bath for phase separation and curing. After phase separation, a raw membrane is obtained. The coagulation bath includes a good phase separation solvent and a phase separation non-solvent. The concentration of the phase separation non-solvent in the coagulation bath is 70~95wt%, and the phase separation curing time is 40-150s. S5, film formation; The raw membrane was washed with pure water and then dried to obtain the PES filter membrane.

15. The preparation process of an asymmetric PES filter membrane according to claim 14, characterized in that: There is an air section between steps S2 and S3, and the pretreatment membrane stays in the air section for 1-10 seconds.

16. The preparation process of an asymmetric PES filter membrane according to claim 14, characterized in that: In step S2, the temperature on the carrier side is 1-10°C lower than the pretreatment temperature.

17. The preparation process of an asymmetric PES filter membrane according to claim 14, characterized in that: The solvent, pretreatment solvent, retreatment solvent, and phase separation solvent are all one or a mixture of at least two of the following: butyl lactate, dimethyl sulfoxide, dimethylformamide, caprolactam, methyl acetate, ethyl acetate, N-ethylpyrrolidone, dimethylacetamide, and N-methylpyrrolidone. The pretreatment non-solvent, the retreatment non-solvent, and the phase separation non-solvent are all water; The pore-forming agent is one or a mixture of at least two of polyvinyl alcohol, polyethylene glycol, polyethyleneimine, and polyvinylpyrrolidone.

18. A filter assembly, comprising a housing, characterized in that: The housing is provided with 1-3 layers of asymmetric PES filter membrane as described in any one of claims 1-13.

19. A filter assembly according to claim 18, characterized in that: The housing contains two layers of asymmetric PES filter membranes, which are stacked together.

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