High-voltage-resistant PES filter membrane and preparation process thereof

Abstract

The application relates to a high-pressure-resistant PES filter membrane and a preparation process thereof, which comprises a porous main body, the porous main body comprises a mesoporous layer, a pre-filter layer and a separation layer in sequence along the thickness direction, the surface of one side of the mesoporous layer is a liquid inlet surface, the SEM average pore diameter of the pre-filter layer is larger than that of the mesoporous layer; the PMI average pore diameter of the filter membrane is 0.15-0.6 microns; a plurality of liquid inlet holes are distributed on the liquid inlet surface, the SEM average pore diameter K of the liquid inlet hole is 0.2-1.5 microns, and the hole area rate of the liquid inlet surface is 5-35%; the pore diameter of the liquid inlet hole is not less than 1.5K, which is a main liquid inlet hole, and the hole area rate of the main liquid inlet hole is 2-25%. After the mesoporous layer is introduced into the filter membrane, the mechanical property of the filter membrane is obviously improved, so that the pore structure of the porous main body on the liquid inlet surface and near the liquid inlet surface of the filter membrane does not deform too much under high pressure, so that the filter membrane still maintains a large effective flow channel area, and the high flux and high load of the filter membrane are ensured.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a high-pressure-resistant PES filter membrane and its preparation process. 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. To ensure good retention of impurities and bacteria in the feed solution, this symmetrical PES filter membrane should not have excessively large pore structures. However, smaller pore structures cause large particles of impurities in the feed solution to be concentrated and retained near the inlet surface, rapidly clogging the membrane pore structure. Therefore, symmetrical filter membranes often have lower dirt-holding capacity (low load capacity) and lower flux (low filtration efficiency).

[0005] Compared to symmetrical filter membranes, asymmetrical filter membranes often exhibit better flux and loading capacity due to their large pore regions with greater dirt-holding capacity and small 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, with the diameter of the flow channels in the porous support structure gradually increasing from the first surface to the second surface. The filter membrane disclosed in the aforementioned patent is a typical asymmetric filter membrane. The pore size of the porous body near the second surface (liquid inlet surface) of the filter membrane and the diameter of the flow channel through which the feed liquid flows are relatively large. On the one hand, this increases the flux of the filter membrane. On the other hand, the filter membrane has a larger dirt-holding space, 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, that is, increasing the load capacity of the filter membrane.

[0006] Generally, the filtration method of the above-mentioned filter membrane (asymmetric flat sheet membrane) is dead-end filtration. In actual use, the feed liquid is often pressurized to obtain a greater filtration driving force, thereby ensuring higher filtration efficiency. It is generally believed that the greater the feed liquid pressure, the greater the rate at which the feed liquid passes through the filter membrane, and the greater the flux of the filter membrane.

[0007] However, the inventors of this application found that when using the aforementioned filter membrane, while the flux of the filter membrane did initially increase to some extent with the increase of the feed pressure, the flux and load of the filter membrane decreased with further increases in the feed pressure. This may be because the large pores on the second surface (inlet surface) of the filter membrane, while giving it higher load and flux, inevitably lead to some loss of mechanical properties. Under high pressure, the porous structure of the filter membrane on the inlet surface may deform or even collapse, reducing the effective area for feed liquid flow and thus decreasing the flux and load of the filter membrane.

[0008] To address these issues, researchers typically employ the following approach: appropriately reducing the pore size of the macropore region of the filter membrane to ensure that the porous body near the liquid inlet surface of the filter membrane possesses higher mechanical properties. However, smaller pore sizes mean increased resistance to the feed liquid in the macropore region and a decrease in the dirt-holding capacity, with the expected result still being a decrease in the flux and load capacity of the filter membrane.

[0009] Therefore, obtaining a PES filter membrane that still has high flux and high load capacity under high pressure is a current technical challenge. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the present invention aims to provide a high-pressure-resistant PES filter membrane and its preparation process, which exhibits high flux and high dirt-holding capacity (high loading capacity). To achieve the above objective, the present invention provides the following technical solution:

[0011] In a first aspect, this application provides a high-pressure-resistant PES filter membrane, which adopts the following technical solution:

[0012] A high-pressure-resistant PES filter membrane includes a porous body with non-directional tortuous pathways within it. One side and the other side of the porous body are liquid inlet surfaces. The porous body sequentially comprises a mesoporous layer, a pre-filtration layer, and a separation layer along its thickness direction. One side of the mesoporous layer is the liquid inlet surface. The SEM average pore size of the pre-filtration layer is larger than that of the mesoporous layer. The PMI average pore size of the filter membrane is 0.15-0.6 μm.

[0013] The liquid inlet surface is provided with a number of liquid inlet holes, the average SEM pore diameter K of the liquid inlet holes is 0.2-1.5μm, and the pore area ratio of the liquid inlet surface is 5-35%; among the liquid inlet holes, those with a pore diameter of not less than 1.5K are the main liquid inlet holes, and the pore area ratio of the main liquid inlet holes on the liquid inlet surface is 2-25%.

[0014] 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 mesoporous layer with a larger pore size, a pre-filtration layer with the largest pore size, and a separation layer with the smallest pore size can be seen sequentially. The overall pore size of the filter membrane first increases and then decreases. There is a critical surface between the pore size increase and decrease. The area between the liquid inlet surface and the critical surface is the mesoporous layer. The mesoporous layer, pre-filtration layer, and separation layer are transitioned by continuous fibers. "Continuous" means that basically all the fibers are interconnected as a whole, as if formed in one 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 mesoporous layer and pre-filtration layer are used to trap large particulate impurities in the feed liquid, preventing them from clogging the separation layer and thus increasing the service life of the filter membrane. The separation layer is used to trap bacteria. The filter membrane of this application has an average pore size of 0.15-0.6 μm (PMI), which has a good filtration effect on bacteria. Furthermore, depending on the required retention effect, the filter membrane of this application can be used as a single layer or multiple layers stacked together to achieve a longer service life and greater retention capacity.

[0015] It is generally believed that compared to the pre-filtration layer (macropore layer), the pore size of the mesopore layer is relatively small, making it more prone to clogging. Furthermore, the introduction of a mesopore layer means an extension of the tortuous pathways within the filter membrane, inevitably increasing the resistance to the feed liquid. Therefore, the introduction of a mesopore layer leads to a decrease in both the overall flux and load capacity (dirt-holding capacity) of the filter membrane. However, the inventors of this application unexpectedly discovered that, in actual use under high pressure, the filter membrane provided in this application exhibits a significant increase in both flux and load capacity, which is surprising.

[0016] This is likely because when filter membranes are used for bacterial filtration, dead-end filtration is generally employed. During the filtration process, external pressure is the primary driving force, resulting in the filter membrane being subjected to significant pressure from the feed liquid (especially under high pressure). For filter membranes without a mesoporous layer, the inlet surface is the side closest to the pre-filtration layer. Due to the larger pore size of the pre-filtration layer, its pore structure (especially the porous structure near the inlet surface) is prone to deformation or even collapse under the pressure of the feed liquid. Once the pore structure of the pre-filtration layer deforms or collapses, both its ability to guide the feed liquid (flux) and its dirt-holding capacity (load capacity) will decrease significantly.

[0017] After the introduction of the mesoporous layer into the filter membrane, the average pore size of the mesoporous layer (SEM) is smaller than that of the pre-filtration layer. Therefore, the mesoporous layer has better mechanical properties (pressure resistance) compared to the pre-filtration layer. With the introduction of the mesoporous layer, the inlet surface is the side closest to the mesoporous layer. This inlet surface has inlet holes with a suitable average pore size (average pore size K is 0.2-1.5 μm). However, the inlet holes are not uniform; some main inlet holes with a pore size not less than 1.5K are introduced. These suitable inlet holes (especially the main inlet holes) provide the inlet surface with a suitable effective flow channel area, thus ensuring that the filtrate has a high feed flow rate. It can be understood that for a single inlet hole, if it is approximated as circular, and the pore size is doubled, then the pore area (the area of ​​the flow channel for feed flow) may become four times larger. Even if the average pore size K of the inlet pores on the inlet surfaces of two filter membranes is the same, if one filter membrane has a certain number of main inlet pores (large pores) on its outlet surface, while the other filter membrane has a relatively uniform overall pore size on its outlet surface, then the filter membrane with a certain number of large pores on its outlet surface will have a larger pore area. In other words, the introduction of main inlet pores (the non-uniformity of the inlet pore structure) further improves the overall flux of the filter membrane, which is different from the current conventional understanding that it is desirable for the inlet pores to be more uniform.

[0018] Furthermore, the inlet surface has a suitable pore area ratio (5-35%), indicating that the inlet surface of the filter membrane has a suitable proportion of solid and non-solid parts. This means that the inlet surface and the porous structure near the inlet surface have suitable pressure resistance. Because the inlet surface and the porous structure near the inlet surface have high pressure resistance, under high pressure, compared to filter membranes with the inlet surface in the pre-filtration layer (macropore layer), the filter membrane provided in this application (the filter membrane with an introduced mesopore layer) exhibits significantly reduced pore structure deformation (especially the main inlet pore) at the inlet surface and near the inlet surface. Simultaneously, the high pressure environment also means that the feed liquid has a high flow rate (higher feed liquid filtration driving force). With a fast feed liquid flow rate and minimal deformation of the feed liquid flow path, the filter membrane has a high flux.

[0019] Meanwhile, the pore area ratio of the inlet surface of the filter membrane is 5-35%, and the pore area ratio of the main inlet hole is 2-25%, which are relatively close. This indicates that there are a large number of solid parts around the inlet hole (especially the main inlet hole) to support the pore structure, so that the deformation of the pore structure under high pressure (such as 30Psi or even higher pressure) is relatively small (especially the deformation of the main inlet hole). Large particles of impurities in the feed liquid can pass through the main inlet hole and smoothly enter the pre-filtration layer for interception, thereby reducing the possibility of filter cake formation on the inlet surface of the filter membrane and ensuring the high loading capacity of the filter membrane.

[0020] Furthermore, because the filter membrane of this application introduces a mesoporous layer, the pre-filtration layer, which has the worst pressure resistance, has a mesoporous layer and a separation layer with strong self-supporting capabilities on both sides. This forms a reinforcing layer on both sides of the pre-filtration layer, preventing pore structure deformation under higher pressure. Therefore, compared to filter membranes without a mesoporous layer, the pre-filtration layer collapses under higher pressure, resulting in a significant decrease in dirt-holding capacity and load capacity. The filter membrane with a mesoporous layer in this application still has a large dirt-holding capacity and a large load capacity because the pore structure of the pre-filtration layer is not easily deformed. Therefore, the introduction of the mesoporous layer can actually enable the filter membrane to have an unexpectedly high load capacity.

[0021] If the average pore size of the inlet holes is greater than 1.5 μm and / or the porosity of the inlet holes is greater than 35%, it indicates that the pore size of the inlet holes on the inlet surface is relatively too large and / or the proportion of non-solid parts on the inlet surface is relatively too large. The mechanical properties of the porous matrix near the inlet surface are low. Under high pressure, the pore structure of the filter membrane inlet surface and the porous matrix near the inlet surface may be excessively deformed, or even lead to the collapse of some pore structures. Since the mesoporous layer already has a smaller pore size than the pre-filtration layer, excessive deformation or even collapse will lead to a significant reduction in flux and loading. If the average pore size of the inlet holes is less than 0.2 μm and / or the porosity of the inlet holes is less than 5%, even if no deformation occurs under high pressure, the already insufficient effective flow channels will make it difficult for the feed liquid to enter the filter membrane through the inlet surface. Large particles of impurities are also more likely to accumulate on the surface and form a filter cake, which will also lead to a significant reduction in flux and loading.

[0022] If the inlet orifice is too small (e.g., less than 0.2 μm) and / or the pore area ratio of the inlet orifice is too small (e.g., less than 5%) and / or the pore area ratio of the main inlet orifice is too small (less than 2%), it means that the effective flow channel area for the feed liquid to circulate on the inlet surface is too small, and the flux of the filter membrane cannot be guaranteed. At the same time, this also means that particulate impurities are easily blocked outside the inlet surface of the filter membrane, and particulate impurities easily form a filter cake, thus reducing both the flux and loading capacity of the filter membrane. If the inlet orifice is too large (e.g., greater than 1.5 μm)... If the pore area ratio of the inlet pore (μm) and / or the inlet pore is too small (e.g., greater than 35%) and / or the pore area ratio of the main inlet pore is too large (greater than 25%), it means that there is a relatively large amount of non-solid portion on the inlet surface. The pressure resistance of the porous matrix near the inlet surface cannot be guaranteed. Under high pressure, the pore structure deformation of the inlet surface and the porous matrix near the inlet surface is large, and even pore structure collapse may occur. Once the pore structure is excessively deformed or even collapses, the flux and loading capacity of the filter membrane will both decrease.

[0023] In summary, the inlet surface has inlet holes and main inlet holes with appropriate pore sizes, and the inlet surface has an appropriate pore area ratio for both the inlet holes and the main inlet holes. This ensures that the flux and loading capacity of the filter membrane in this application are significantly improved after the introduction of the mesoporous layer.

[0024] In this application, pores distributed on the inlet surface with a diameter of 0.05-5 μm are defined as inlet 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 diameter is larger than 5 μm, the excessively large pores may lead to bacterial leakage. Therefore, pores on the inlet surface with a diameter larger than 5 μm cannot be defined as inlet pores, and may even be defined as defects.

[0025] When measuring the pore size and porosity of the inlet orifice, the inlet surface of the membrane can be characterized first 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 measure the number, diameter, and area of ​​all liquid inlet holes on this area. The average diameter K of the liquid inlet holes and the porosity of the liquid inlet surface can be obtained by calculation. Of course, those skilled in the art can also obtain the above parameters through other measurement methods, which are for reference only. The porosity of the secondary liquid inlet holes mentioned later can also be obtained by a similar method.

[0026] The average pore size of the filter membrane (PMI) can be directly measured using a PMI pore size meter.

[0027] Optionally, the inlet holes with a diameter not higher than 0.7K are secondary inlet holes, and the pore area ratio of the secondary inlet holes on the inlet surface is 0.4-5%.

[0028] By adopting the above technical solution, since the inlet surface has several main inlet holes (pore diameter not less than 1.5K), meaning the inlet surface contains a "macropore structure," there must also be a portion of "micropore structure" on the inlet surface, thus ensuring that the overall inlet pores of the filter membrane have a suitable average pore diameter (0.2-1.5μm). In this application, inlet holes with a pore diameter less than 0.7K are referred to as secondary inlet holes. Since the pore diameter of the secondary inlet holes is relatively small, this also means that the solid part of the porous body near the secondary inlet holes is relatively large. When the secondary inlet holes are located near the main inlet holes, the porous body near the secondary inlet holes plays a certain reinforcing role on the porous body near the main inlet holes, thereby further improving the overall pressure resistance of the inlet surface, and further reducing the degree of pore structure deformation of the filter membrane inlet surface and the porous body near the inlet surface under high pressure. The flux and loading capacity of the filter membrane are both significantly improved.

[0029] The secondary inlet holes have a suitable pore area ratio, further ensuring the flux and loading capacity of the filter membrane in this application. If the pore area ratio of the secondary inlet holes is too small (e.g., less than 0.4%), it indicates that the number of secondary inlet holes on the overall inlet surface is relatively small and / or the pore size is relatively small. This also means that the number of main inlet holes on the overall inlet surface is relatively small and / or the pore size is relatively large. If the number of secondary and main inlet holes is relatively small, it indicates that the overall flow channel area of ​​the inlet surface is relatively small, and the flux of the filter membrane is not high. If the number of main inlet holes is too small, once impurity particles clog the main inlet holes, the decrease in the flux and loading capacity of the filter membrane may be relatively high. If the secondary inlet hole is relatively small while the main inlet hole is relatively large, the pressure resistance of the porous body near the main inlet hole will be relatively insufficient. Even with the reinforcement effect of the porous body near the secondary inlet hole (there are many solid parts around the main inlet hole, and the solid parts support and reinforce the main inlet hole), under high pressure, the relatively large main inlet hole may still deform to some extent, resulting in low flux and load of the filter membrane.

[0030] If the pore area ratio of the secondary inlet holes is too large (e.g., greater than 5%), it means that the number of secondary inlet holes on the inlet surface is relatively large and / or the pore diameter is relatively large. This indicates that the number of main inlet holes on the inlet surface is relatively large and / or the pore diameter is relatively small. The overall pore structure of the inlet surface is relatively uneven (a relatively large number of large holes and a relatively large number of small holes). An excessive number of secondary inlet holes (small holes) means that the probability of impurity particles clogging the secondary inlet holes and forming a filter cake is relatively high, which will undoubtedly reduce the overall flux and loading capacity of the filter membrane. Similarly, a relatively small pore diameter of the main inlet holes will also lead to a reduction in the overall flux and loading capacity of the filter membrane.

[0031] In summary, the filter membrane inlet surface has secondary inlet holes with suitable pore size and pore area ratio, which, combined with the main inlet holes with suitable pore size and pore area ratio, further ensures the improvement of the filter membrane's flux and load capacity under high pressure environment.

[0032] Optionally, the ratio of the number of main inlet holes to the number of secondary inlet holes is 0.25-0.5.

[0033] By adopting the above technical solution, the number of main inlet holes and secondary inlet holes on the inlet surface has a suitable ratio, indicating that each main inlet hole is near a suitable number of secondary inlet holes, and the porous body near each main inlet hole has a relatively dense solid part. Each main inlet hole receives good reinforcement, meaning that the inlet surface as a whole has good pressure resistance. Under high pressure, the pore structure of the inlet surface and the porous body near the inlet surface (especially the main inlet hole and the porous body near the main inlet hole) deforms relatively little, thus ensuring high flux and high load capacity of the filter membrane.

[0034] If the ratio of the two is too small (less than 0.25), it indicates that the number of main inlet holes is relatively too small while the number of secondary inlet holes is too large, resulting in a relatively small overall effective flow channel area of ​​the inlet surface and an inability to guarantee the flux of the filter membrane. If the ratio of the two is too large (greater than 0.5), it indicates that the number of main inlet holes is relatively too large while the number of secondary inlet holes is too small, resulting in relatively insufficient pressure resistance of the porous body on and near the inlet surface. Under high pressure, the porous body on and near the inlet surface (especially the porous body near the main inlet holes) will deform to a relatively large degree, and the flux and load of the filter membrane cannot be guaranteed.

[0035] Optionally, the pore density ρ of the inlet holes on the inlet surface is 200-900 holes / 1000μm. 2 The number of main inlet holes accounts for 10-20% of the total number of inlet holes.

[0036] By adopting the above technical solution, in addition to having a suitable pore area ratio and average pore diameter K, the inlet holes also have a suitable pore density ρ (pore density ρ represents the number of inlet holes per unit area). This indicates that the inlet holes on the inlet surface are uniformly distributed. At the same time, the inlet holes also include a suitable number of main inlet holes. With the combined effect of these four factors, it is ensured that each unit area of ​​the inlet surface has a suitable area of ​​solid and non-solid parts, thereby ensuring that each unit area has sufficient flow channel area and mechanical strength, and thus ensuring the overall flux and loading capacity of the filter membrane.

[0037] If the pore density ρ in a certain area of ​​the liquid inlet surface is too small (ρ less than 200 pores / 1000μm) 2 If the proportion of the main inlet orifice is relatively small (less than 10%), it indicates that the solid portion of this unit area is relatively large, the effective flow channel area for the feed liquid entering this unit area is relatively small, and the flux and loading capacity of this area are not high, thus affecting the overall flux and loading capacity of the filter membrane; if the pore density ρ of a certain area of ​​the inlet surface is too large (ρ greater than 900 pores / 1000μm), it indicates that the main portion of the filter membrane is relatively large, the effective flow channel area for the feed liquid entering this unit area is relatively small, and the flux and loading capacity of this area are not high, thus affecting the overall flux and loading capacity of the filter membrane. 2 If the proportion of large pores is relatively high (e.g., greater than 20%), it indicates that the solid part of this area is relatively small, the mechanical properties of this area are deviated, and under high pressure, the deformation degree of the pore structure (especially the large pore structure) in this area is relatively high. The flux and load of this area are both reduced, which in turn affects the overall flux and load of the filter membrane.

[0038] When measuring the pore density ρ of the inlet orifice, the inlet surface of the membrane can be characterized first 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, and then use the corresponding computer software or manually to measure the number of all liquid inlet holes on this area. The pore density ρ of the liquid inlet holes can be obtained by calculation. 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.

[0039] Optionally, the inlet holes with a diameter of not less than 3K are considered extra-large inlet holes, and the number of extra-large inlet holes on the inlet surface accounts for 1-3% of the total number of inlet holes.

[0040] By adopting the above technology, when there are only a few extra-large inlet holes on the inlet surface, the flux and loading capacity of the filter membrane will be further improved during use.

[0041] This is likely because larger particulate impurities in the feed solution can enter the interior of the filter membrane through the extra-large inlet holes and be trapped by the hollow layer or pre-filtration layer of the filter membrane, rather than forming a filter cake on the filter membrane surface and reducing the filter membrane flux. Therefore, this application preferably has a very small number of extra-large inlet holes near the inlet surface, rather than the absence of extra-large inlet holes.

[0042] Of course, the presence of extra-large inlet holes means that the proportion of non-solid parts in the porous matrix near the extra-large inlet holes is relatively large, and the mechanical properties of the porous matrix near the extra-large inlet holes are relatively low. Therefore, the number of extra-large inlet holes should not be too large to ensure that the overall inlet surface still has high mechanical strength, thereby ensuring that the filter membrane inlet surface will not undergo excessive deformation during actual use (especially the main inlet holes and extra-large inlet holes), thus ensuring the overall flux and load capacity of the filter membrane.

[0043] In summary, the inlet surface of the filter membrane has inlet holes and main inlet holes of appropriate size, number, and density, and the inlet surface has only a very small number of ultra-large inlet holes. Under the combined effect of these three factors, the inlet surface of the filter membrane is further guaranteed to have appropriate effective flow channel area and mechanical strength, thereby ensuring high flux and high load capacity in actual use of the filter membrane.

[0044] Optionally, the thickness of the mesoporous layer is 8-20 μm, and the pore area ratio of the cross-section of the mesoporous layer is 10-25%.

[0045] By adopting the above technical solution, the mesoporous layer has a suitable thickness and a suitable pore area ratio, indicating that the mesoporous layer as a whole has a relatively suitable density (the density of the mesoporous layer specifically refers to the ratio of the volume of the solid part of the membrane per unit area to the volume of the non-solid part). The mesoporous layer has relatively suitable mechanical properties, and at the same time, the mesoporous layer has a suitable number of channels for guiding the flow of the feed liquid, as well as a suitable space for accommodating impurity particles, thereby ensuring that the filter membrane as a whole has a high flux and loading capacity.

[0046] If the thickness of the mesoporous layer is too thin (e.g., less than 8 μm) and / or the pore area ratio of the mesoporous layer is too large (e.g., greater than 25%), the overall mechanical properties of the mesoporous layer are relatively insufficient. Under high pressure, the overall deformation of the mesoporous layer of the filter membrane may be relatively high, which may significantly reduce the overall flux and loading capacity of the filter membrane. If the thickness of the mesoporous layer is too thick (e.g., greater than 20 μm) and / or the pore area ratio is too small (e.g., less than 10%), the overall density of the mesoporous layer is relatively low, and the number of channels in the mesoporous layer used to guide the flow of the feed liquid is relatively small. Once the channels are blocked, the overall flux and loading capacity of the filter membrane will be greatly reduced.

[0047] Optionally, the average SEM pore size of the pores in the mesoporous layer cross-section is 0.8-3 μm, and the average SEM pore size of the mesoporous layer gradually increases along the direction of liquid flow.

[0048] By adopting the above technical solution, the pore size of the mesoporous layer gradually increases along the direction of liquid flow. This indicates that the pore size on the side of the mesoporous layer closest to the liquid inlet surface is relatively the smallest, meaning that the solid portion of the mesoporous layer near the liquid inlet surface accounts for a relatively large proportion, resulting in relatively good pressure resistance and low overall deformation of the mesoporous layer. Simultaneously, the mesoporous layer also possesses a suitable average pore size. Combined with a suitable pore area ratio and thickness, this further ensures appropriate density. Furthermore, the presence of inlet holes, main inlet holes, and extra-large inlet holes on the liquid inlet surface with relatively low deformation and suitable pore size, number, and density further guarantees high flux and high loading capacity of the filter membrane.

[0049] It can be understood that the average pore size and porosity of the mesoporous layer can be measured by the following method: first, the cross-section of the PES filter 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 manually measure the pore diameter of all holes in this area, and calculate their average value to obtain the average pore diameter of the mesoporous layer of this cross section. At the same time, measure the area of ​​all holes in this area, and calculate the pore area ratio of the mesoporous layer of this cross section. The average pore diameter and pore area ratio of the pre-filter layer will be discussed later.

[0050] Optionally, along the direction of feed flow, the average pore size variation gradient of the mesoporous layer measured by SEM is 0.08-0.15 μm / μm.

[0051] By adopting the above technical solution, the mesoporous layer possesses a suitable average pore size variation gradient along the flow direction of the feed liquid. That is, the average pore size (density) of the mesoporous layer changes slowly with thickness, and the density gradually decreases without abrupt changes. Specifically, the average pore size variation gradient refers to the change in average pore size per unit thickness. The larger this value, the faster the pore size changes with thickness; the smaller the value, the smaller the change in pore size with membrane thickness. The average pore size variation gradient is calculated by dividing the difference between the maximum and minimum pore sizes (in μm) within a certain region by the thickness between them (the distance between the maximum and minimum pore sizes within that region, in μm). Note: If there is a certain thickness at the minimum pore size within that region, the thickness between the two locations refers to the minimum thickness between the maximum and minimum pore sizes.

[0052] If the change value is too small (less than 0.08 μm / μm), it means that the overall pore size of the mesoporous layer is relatively small and the mesoporous layer is relatively dense. After introducing a relatively dense mesoporous layer with a certain thickness into the filter membrane, the flux and loading capacity of the filter membrane will not be high. If the change value is too large (greater than 0.15 μm / μm), it means that the overall pore size of the mesoporous layer is too large and the overall mechanical properties of the mesoporous layer are low. Under the action of high feed liquid pressure, the probability of excessive deformation or even collapse of the pore structure of the mesoporous layer is relatively high. Once the pore structure is excessively deformed or collapses, the flux and loading capacity of the filter membrane will be significantly reduced.

[0053] Optionally, the mesoporous layer includes supporting fibers, which are interconnected to form a three-dimensional network structure of the mesoporous layer. The SEM average diameter of the supporting fibers is 0.2-0.9 μm, and the ratio of the SEM average pore diameter of the pores in the cross-section of the mesoporous layer to the SEM average diameter of the supporting fibers is 1.5-4.5.

[0054] By adopting the above technical solution, the mesoporous layer has supporting fibers of suitable thickness, further ensuring high flux and high loading capacity. If the supporting fibers are too fine (less than 0.2 μm), they cannot effectively support the pore structure of the mesoporous layer, resulting in relatively insufficient overall mechanical properties. Under high feed pressure, the pore structure of the mesoporous layer is more likely to deform excessively or even collapse. Once the pore structure is excessively deformed or collapses, the flux and loading capacity of the filter membrane will be significantly reduced. If the supporting fibers are too coarse (greater than 0.9 μm), they will create significant resistance to the feed, meaning that the introduction of the mesoporous layer leads to a lower overall flux of the filter membrane.

[0055] Meanwhile, there should be a suitable ratio between the average pore size of the mesoporous layer and the average diameter of the supporting fibers. If the ratio is too small, it means that the average pore size of the mesoporous layer is relatively small and / or the supporting fibers are relatively coarse, that is, the overall density of the mesoporous layer is relatively high. The introduction of the mesoporous layer will lead to a lower overall flux and loading capacity of the filter membrane. If the ratio is too large, it means that the average pore size of the mesoporous layer is relatively large and / or the supporting fibers are relatively fine. The excessively fine mesoporous layer fibers cannot provide sufficient support for the relatively large pores of the mesoporous layer. The overall mechanical properties of the mesoporous layer are relatively insufficient. Under the action of high feed liquid pressure, the probability of excessive deformation or even collapse of the pore structure of the mesoporous layer is relatively high. Once the pore structure is excessively deformed or even collapses, the flux and loading capacity of the filter membrane will be significantly reduced.

[0056] It can be understood that the diameter of the supporting fibers can be measured by the following method: first, the cross-section of the PES filter 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 manually measure the diameter of all supporting fibers in this area, and then calculate the average value to obtain the average diameter of the supporting fibers in this cross section.

[0057] Optionally, the thickness of the pre-filter layer is 60-90 μm, the SEM average pore size of the pre-filter layer cross-section is 1-5 μm, and the pore area ratio of the pre-filter layer cross-section is 25%-45%.

[0058] By adopting the above technical solution, the pre-filter layer possesses suitable thickness, average pore size, and pore area ratio, indicating that the pre-filter layer as a whole has a relatively suitable density, thus ensuring that the pre-filter layer as a whole has a high flux and relatively high mechanical strength. Simultaneously, since the pre-filter layer is located between the mesoporous layer and the separation layer, a portion of the pressure borne by the pre-filter layer is dispersed into the mesoporous layer and the separation layer (the pores in the mesoporous layer and the separation layer are relatively small, and their self-supporting performance is relatively high). This prevents excessive deformation of the membrane structure under high pressure, further ensuring a significant improvement in the overall flux of the filter membrane.

[0059] Optionally, the porous body includes a protective layer, the separation layer is located between the pre-filter layer and the protective layer, the SEM average pore size of the protective layer is larger than the SEM average pore size of the separation layer, and the thickness of the protective layer is 12-20 μm.

[0060] By adopting the above technical solution, after the protective layer is introduced into the porous body, the porous membrane comprises four layers along the feed flow direction: a mesoporous layer, a pre-filtration layer, a separation layer, and a protective layer. The pore size of the filter membrane gradually increases, then decreases, and then gradually increases again. After the protective layer is introduced, the separation layer is located between the pre-filtration layer and the protective layer, rather than being exposed on the surface of the PES filter membrane. Furthermore, the thickness of the protective layer is not less than 12 μm. The protective layer of appropriate thickness protects the separation layer (external mechanical damage often requires the protective layer to be damaged before further damaging the separation layer structure). Even if the protective layer structure is damaged, as long as the separation layer structure is not damaged, the risk of bacterial leakage from the PES filter membrane remains low. Therefore, the setting of the protective layer greatly reduces the possibility of bacterial leakage due to external mechanical damage.

[0061] Secondly, this application provides a process for preparing a high-pressure-resistant PES filter membrane, which adopts the following technical solution:

[0062] 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: 20-50 parts of polyethersulfone resin, 50-80 parts of casting solution solvent and 10-25 parts of pore-forming agent; the casting solution temperature is 35-60℃.

[0063] S2. Pretreatment: The carrier loaded with the liquid film is placed in a pretreatment bath for 5-15 seconds to obtain a pretreated membrane. The pretreatment bath includes a good pretreatment solvent and a non-pretreatment solvent, with the concentration of the good pretreatment solvent in the pretreatment bath being 45-65 wt%.

[0064] S3. First-stage curing: The carrier loaded with the pretreated film is placed in a pre-coagulation bath for phase separation and curing. After phase separation, a film is obtained. The pre-coagulation bath includes a good pre-coagulation solvent and a non-solvent for pre-coagulation. The concentration of the non-solvent for pre-coagulation in the pre-coagulation bath is 70~95wt%. The first-stage curing time is 5-20s.

[0065] S4. Reprocessing: The carrier loaded with the biofilm is placed in a reprocessing bath for reprocessing for 5-25 seconds to obtain a reprocessed 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 80-95 wt%.

[0066] S5. Secondary curing: The carrier loaded with the reprocessed film is placed in a re-coagulation bath for phase separation and curing. After phase separation is completed, a film is obtained. The re-coagulation bath includes a non-solvent for re-coagulation. The secondary curing time is 40-80 seconds.

[0067] S6. Post-treatment: The membrane is washed with pure water and then dried to obtain the PES filter membrane.

[0068] By adopting the above technical solution, the first step in preparing the PES filter membrane is the preparation of the casting solution. In this application, by controlling the mass fraction of each substance in the casting solution, the casting solution is guaranteed to have a suitable solid content (the solid content refers to the mass ratio of polyethersulfone in the casting solution). Furthermore, by controlling the temperature of the casting solution, the casting solution is made to have a suitable viscosity and fluidity, which facilitates the subsequent phase separation and curing steps.

[0069] The second step involves pretreating the air side of the liquid membrane in a pretreatment bath (one-time treatment). The third step involves a pre-coagulation bath to solidify the liquid membrane after the first treatment. After the first treatment and solidification, the liquid membrane forms the mesoporous layer required for the PES filter membrane of this application. It is understandable that because the pretreatment bath contains a relatively high content of good pretreatment solvent, the good pretreatment solvent dilutes the air side of the liquid membrane, appropriately reducing the solid content in the casting solution on the air side. However, the liquid membrane undergoes phase separation in the pretreatment bath but does not undergo excessive solidification (or even no solidification). During the pretreatment process, the appropriate concentration and time of the good pretreatment solvent allow the air side of the liquid membrane (i.e., the inlet surface) to initially form a polymer-rich phase and a solvent-rich phase of suitable size (with a tendency to initially form the main inlet pore). After dilution, the inlet surface of the liquid membrane initially forms the main inlet pore structure required by this application, while also appropriately reducing the solid content near the inlet surface, thus allowing the inlet surface to initially form the inlet pore structure required by this application.

[0070] Next, the liquid film enters the pre-coagulation bath, where the content of the pre-coagulated non-solvent is relatively high, and the liquid film begins to solidify. Due to the relatively high non-solvent content of the pre-coagulated non-solvent, the phase separation rate is relatively fast, resulting in relatively uneven pores (i.e., forming both the main inlet pores and the secondary inlet pores required in this application). Through the synergistic effect of the pretreatment and primary curing steps, the liquid film forms the mesoporous layer with the uneven pore structure required in this application. Furthermore, by controlling the primary curing time and combining it with a suitable casting solution viscosity, the thickness of the mesoporous layer can be further controlled; the longer the primary curing time, the thicker the mesoporous layer. In addition, because this application reasonably controls the pretreatment time (5-15s), the liquid film inlet surface is not completely phase-separated. The unseparated areas undergo relatively rapid phase separation and solidification in the pre-coagulation bath, forming the secondary inlet pores required in this application.

[0071] The fourth step is to re-treat the air side of the biofilm in a reprocessing bath (secondary treatment). The fifth step is to re-solidify the biofilm after secondary treatment in a re-coagulation bath, thereby forming the pre-filtration layer and separation layer required for the PES filter membrane of this application. After the biofilm enters the reprocessing bath, the reprocessing solvent enters the interior of the biofilm through the mesoporous layer. The reprocessing solvent dilutes the casting solution inside the biofilm. Since the content of the reprocessing solvent in the reprocessing bath is significantly higher than that in the preprocessing bath, the size of the polymer-rich phase and solvent-rich phase formed in the reprocessed membrane will be significantly larger than the size of the polymer-rich phase and solvent-rich phase in the preprocessed membrane. It is understandable that, due to the appropriate time (5-25s) for the biofilm to enter the reprocessing bath during the reprocessing step, along the liquid film thickness direction (from the air side to the carrier side), the portion of the casting solution near the mesoporous layer will be diluted by the reprocessing bath, while the portion of the casting solution far from the mesoporous layer will not be diluted by the reprocessing bath (or the degree of dilution is very small). Therefore, after the recoagulation bath enters the membrane formation process, it first contacts the diluted casting solution, and this portion of the casting solution solidifies to form the pre-filtration layer of the filter membrane of this application. Immediately afterwards, the recoagulation bath penetrates through the pre-filtration layer and permeates into the membrane formation process (contacting the undiluted casting solution). This portion of the casting solution solidifies under the action of the recoagulation bath, thereby forming the separation layer in the filter membrane of this application.

[0072] Meanwhile, the inventors of this application discovered that if the thickness of the liquid film is relatively large, after the separation layer is formed by the recoagulation bath, a portion of the liquid film will still not be separated and solidified. Since the pore size of the separation layer is small, the recoagulation bath is subject to greater resistance from the separation layer, the recoagulation bath permeation rate decreases, and the phase separation rate slows down, thereby forming a protective layer on the carrier side, that is, forming a four-layer filter membrane (viewed along the membrane thickness direction, the pore size of the filter membrane first increases, then decreases, and then increases again).

[0073] The sixth step is the post-processing step, which involves washing the membrane with pure water and finally drying it to obtain the PES filter membrane.

[0074] Optionally, in step S2, the temperature of the pretreatment bath is 1-10°C higher than the temperature of the casting solution, and in step S3, the temperature of the pre-coagulation bath is 10-20°C lower than the temperature of the casting solution.

[0075] By adopting the above technical solution, when the casting solution comes into contact with the pretreatment bath, the temperature of the pretreatment bath is higher than that of the casting solution. Therefore, under the action of the pretreatment bath, the temperature of the casting solution is appropriately increased and the viscosity of the casting solution is appropriately reduced. The pretreatment solvent can more easily enter the interior of the liquid film from the air side of the liquid film, and the pretreatment solvent can more easily dilute the air side of the liquid film, thereby forming a main liquid inlet hole and an ultra-large liquid inlet hole with a more suitable pore size.

[0076] The temperature of the pre-coagulation bath is lower than that of the casting solution. After the pretreated membrane enters the pre-coagulation bath, under the action of thermodynamic driving force, the pretreated membrane has a relatively fast phase separation rate. The faster the phase separation rate, the easier it is to form a non-uniform pore structure. At the same time, since the casting solution has been diluted by the pre-coagulation bath, even if the phase separation rate is fast, the pore size formed will not be too small. Under the synergistic effect of a suitable casting solution system, a suitable pre-coagulation bath, and a suitable pre-coagulation bath, a mesoporous layer with a non-uniform pore structure required for the filter membrane of this application is formed.

[0077] It is understandable that the phase separation rate of the liquid film is affected by a variety of factors, such as temperature (including liquid film temperature and ambient temperature) and viscosity. When the temperature decreases slightly, the viscosity of the casting solution increases. At this time, the effect of the casting solution viscosity on the phase separation rate is greater than the effect of thermodynamic factors on the phase separation rate. Although the temperature decreases, the phase separation rate of the liquid film also decreases slightly. However, when the temperature decreases significantly, thermodynamic factors become dominant. At this time, the effect of temperature on the phase separation rate is greater than the effect of the casting solution on the phase separation rate, and the phase separation rate of the liquid film becomes faster.

[0078] Optionally, the temperature difference between the pretreatment bath and the pre-coagulation bath is 10-25℃.

[0079] By adopting the above technical solution, the pretreatment bath and the pre-coagulation bath have a suitable temperature difference, so that the mesoporous layer (especially the liquid inlet surface) of the prepared filter membrane can be prepared with a more ideal pore structure (this application prefers that the pore structure of the mesoporous layer of the filter membrane is not uniform, but not excessively non-uniform).

[0080] If the temperature difference between the two is too large (e.g., greater than 25℃), it indicates that the temperature of the pretreatment bath is relatively too high and / or the temperature of the pre-coagulation bath is relatively too low. If the temperature of the pretreatment bath is relatively too high, the dilution degree on the air side of the liquid film is relatively too large, resulting in excessively large sizes of the solvent-rich and polymer-rich phases. If the temperature of the pre-coagulation bath is too low, it means that the phase separation rate on the air side of the liquid film is too fast, resulting in excessively uneven pores. Under the combined effect of these two factors, the pore size of the main inlet pores in the mesopore layer of the filter membrane (especially the inlet surface) may be too large while the pore size of the secondary inlet pores is too small. The pore structure of the mesopore layer (especially the inlet surface) is excessively uneven, and the flux and loading of the filter membrane cannot be significantly improved.

[0081] If the temperature difference between the two is too small (e.g., less than 10℃), it indicates that the temperature of the pretreatment bath is relatively too low and / or the temperature of the pre-coagulation bath is relatively too high. If the temperature of the pretreatment bath is relatively too low, the size of the solvent-rich phase and polymer-rich phase formed will be too small; if the temperature of the pre-coagulation bath is too high, it means that the phase separation rate on the air side of the liquid film is too slow, and the pores formed are too uniform. Under the combined effect of the two, it may be possible that the pore layer in the filter membrane (especially the liquid inlet surface) does not have obvious main liquid inlet pores and secondary liquid inlet pores, and the flux and loading of the filter membrane cannot be significantly improved.

[0082] Optionally, the recoagulation bath may further include a good recoagulation solvent, and the concentration of the non-solvent in the recoagulation bath is 80-95 wt%.

[0083] By adopting the above technical solution and controlling the concentration of the coagulation non-solvent in the recoagulation bath, the size of the pore structure of the separation layer of the filter membrane of this application can be reasonably controlled, thereby enabling the filter membrane of this application to meet different application scenarios.

[0084] Optionally, the casting solution solvent, pretreatment solvent, pre-coagulation solvent, retreatment solvent, and re-coagulation 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.

[0085] The pretreatment non-solvent, the pre-coagulation non-solvent, the retreatment non-solvent, and the re-coagulation non-solvent are all water;

[0086] The pore-forming agent is one or a mixture of at least two of polyvinyl alcohol, polyethylene glycol, polyethyleneimine, and polyvinylpyrrolidone.

[0087] The present application provides the following beneficial effects: the PES filter membrane exhibits high pressure resistance; under high pressure, the inlet surface and the porous structure near it do not undergo excessive deformation, thus ensuring high flux and high loading capacity. Furthermore, in practical use, the filter membrane also possesses high bacterial retention performance. The preparation method provided by this invention allows for convenient, rapid, and effective preparation of the aforementioned filter membrane. Attached Figure Description

[0088] Figure 1 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the PES filter membrane (four-layer structure filter membrane) prepared in Example 1, with a magnification of 700×.

[0089] Figure 2 This is a schematic diagram of the liquid inlet surface of the PES filter membrane prepared in Example 1, with a magnification of 2000×.

[0090] Figure 3 This is a scanning electron microscope (SEM) schematic diagram of the cross-section of the PES filter membrane (two-layer structure filter membrane) prepared in Comparative Example 3, with a magnification of 500×.

[0091] Figure 4 This is a schematic diagram of the apparatus for testing the PES filter membrane loading in this application. Detailed Implementation Example 1

[0092] This application discloses a high-pressure-resistant PES filter membrane, which is prepared using the following process steps:

[0093] 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: 36 parts polyethersulfone resin, 64 parts solvent and 16 parts pore-forming agent; the casting solution temperature is 45℃; the solvent is butyl lactate and the pore-forming agent is polyvinyl alcohol.

[0094] S2. Pretreatment: The carrier loaded with the liquid film is placed in a pretreatment bath for pretreatment for 8 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 55 wt%. The good pretreatment solvent is butyl lactate, and the non-pretreatment solvent is water. The temperature of the pretreatment bath is 48°C.

[0095] S3. One-time curing: The carrier loaded with the pretreated film is immersed in a pre-coagulation bath for phase separation and curing. After phase separation, a green film is obtained. The pre-coagulation bath includes a good pre-coagulation solvent and a non-coagulation solvent. The concentration of the non-coagulation solvent in the pre-coagulation bath is 85 wt%, and the one-time curing time is 12 s. The good pre-coagulation solvent is butyl lactate, and the non-coagulation solvent is water. The temperature of the pre-coagulation bath is 32℃.

[0096] S4. Reprocessing: The carrier loaded with the biofilm is placed in a reprocessing bath for reprocessing for 14 seconds to obtain a reprocessed 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 88 wt%. The good reprocessing solvent is butyl lactate, and the non-reprocessing solvent is water.

[0097] S5. Secondary curing: The carrier loaded with the reprocessed film is immersed in a re-coagulation bath for phase separation and curing. After phase separation, a film is obtained. The re-coagulation bath includes a good re-coagulation solvent and a non-re-coagulation solvent. The concentration of the non-re-coagulation solvent is 90 wt%, and the secondary curing time is 60 s. The good re-coagulation solvent is butyl lactate, and the non-re-coagulation solvent is water.

[0098] S6. Post-treatment: The membrane is washed with pure water and then dried to obtain the PES filter membrane.

[0099] Examples 2-7

[0100] 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.

[0101] It should be noted that in Example 4, the temperature of the pretreatment bath in the S2 pretreatment step is the same as the temperature of the casting liquid, and the temperature of the pre-solidification bath in the S3 primary curing step is the same as the temperature of the casting liquid. Comparative Example 1

[0102] 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. Comparative Example 2

[0103] The difference between Comparative Example 2 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 2 does not include a pretreatment step; the carrier loaded with the liquid film is directly immersed in the pretreatment bath for phase separation and solidification. Comparative Example 3

[0104] The filter membrane of Comparative Example 3 was prepared using the following process steps:

[0105] 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: 35 parts polyethersulfone resin, 64 parts solvent and 17 parts pore-forming agent; the casting solution temperature is 60℃; the solvent is butyl lactate and the pore-forming agent is polyvinyl alcohol.

[0106] S2. Pretreatment: In an environment with a temperature of 40°C, an airflow with an absolute humidity of 20 g H2O / kg is blown onto the surface of the liquid film for treatment. The relative velocity between the airflow and the liquid film is 1.5 m / min, and the duration is 45 s, to obtain a pretreated film.

[0107] S3: Phase separation curing. The pretreated membrane is immersed in water at a temperature of 20°C for 60 seconds to achieve phase separation curing, thus obtaining the film.

[0108] S4. Post-treatment: The membrane is washed with pure water and then dried to obtain the PES filter membrane.

[0109] The filter membrane formed in Comparative Example 3 consists only of a pre-filtration layer and a separation layer, and is a typical V-shaped asymmetric membrane.

[0110] Table 1. Casting solution formulations for each embodiment and comparative example.

[0111] polyethersulfone resin mass fraction Solvent mass parts Pore-forming agent mass fraction Casting solution temperature / ℃ Solid content / % Example 1 36 64 16 45 31.03 Example 2 38 66 14 42 32.20 Example 3 32 76 12 36 26.67 Example 4 45 74 22 44 31.91 Example 5 22 77 11 55 20.00 Example 6 50 78 20 40 33.78 Example 7 30 80 10 60 25.00 Comparative Example 1 45 73 25 50 31.47 Comparative Example 2 34 65 18 65 29.06 Comparative Example 3 35 64 17 60 30.17

[0112] Table 2. Process parameters for each embodiment and comparative example.

[0113] Preprocessing time / s Pretreatment solvent concentration / wt% Pretreatment bath temperature / °C Curing time per second Pre-solvent concentration / wt% Pre-coagulation bath temperature / ℃ Temperature difference between pretreatment bath and pre-coagulation bath / ℃ Reprocessing time / s Pretreatment solvent concentration / wt% Secondary curing time / s Re-solvent concentration / wt% Example 1 8 55 48 12 85 32 16 14 88 60 88 Example 2 10 60 50 13 92 28 22 16 91 65 90 Example 3 12 46 38 14 80 18 20 9 84 52 92 Example 4 9 52 48 9 94 34 14 15 90 55 91 Example 5 6 45 55 18 75 55 0 23 94 77 82 Example 6 5 65 49 6 95 32 17 6 80 42 95 Example 7 15 62 70 15 70 50 20 20 89 70 80 Comparative Example 1 8 75 65 9 65 25 40 14 92 54 90 Comparative Example 2 / / / 16 60 60 / 15 86 58 90

[0114] Performance testing and data

[0115] The detection methods are as follows:

[0116] PMI average pore size: The PES filter 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.

[0117] Flux: The PES filter membranes prepared in each example and comparative example were used as samples. The samples (the filter membranes to be tested) were cut into membrane sheets with a diameter of 47 mm. The membrane sheets were placed in an environment with a temperature of 20°C and a pressure of 30 psi, and the time required for 50 ml of water to pass through the membrane sheets was measured. The 30 psi pressure test environment can be considered a relatively high pressure environment. For example, in the European invention patent document with authorization publication number EP1149624B1 (applied by Parr Corporation), the water permeability (flux test) of the filter membrane was tested at 6 psi (approximately 41.2 kPa).

[0118] Load capacity:

[0119] ①: Membrane preparation; take the PES filter membranes prepared in each example and comparative example as samples, and cut the samples (the filter membranes to be tested) into membranes with a diameter of 47 mm;

[0120] ②: Test setup (test setup such as...) Figure 4 ); Load the filter membrane into the membrane holder and assemble the device in the following order: gas source → pressure regulating valve → pressure gauge → pressure vessel → φ47mm membrane holder → liquid collection container, place the liquid collection container on the electronic balance;

[0121] ③: Pour the test solution into the pressure vessel and adjust the pressure to 30 psi. The test solution is a 0.1% BSA protein solution.

[0122] ④: Place the liquid collection container on the electronic balance and tare it, open the valve of the pressure vessel, and immediately start the automatic counting device;

[0123] ⑤: Record the change in membrane filtration quality as filtration time increases. Record once every 10 seconds in the first minute, once every 30 seconds from the first to the tenth minute, and once every minute thereafter. Stop filtration when the material filtration flow rate decreases to 90%. Record the change in membrane filtration quality over time, and calculate the filtration volume of the test solution using the density of the test solution.

[0124] 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.

[0125] The morphological parameters of the PES filter membranes prepared in each embodiment and comparative example are detailed in Tables 3 and 4, and the performance parameters are detailed in Table 5.

[0126] Table 3. Morphological parameters of the inlet surface of the PES filter membranes prepared in each embodiment and comparative example.

[0127] Average pore diameter of inlet hole K / μm Liquid inlet surface porosity / % Main inlet hole area ratio of liquid inlet surface / % Inlet surface secondary inlet hole porosity ratio / % The ratio of the number of primary to secondary inlet holes Inlet porosity ρ Percentage of main inlet holes / % Percentage of extra-large inlet holes / % Example 1 0.56 17.3 10.2 0.98 0.32 536 14.2 1.4 Example 2 0.67 19.5 8.7 0.35 0.34 438 12.3 1.1 Example 3 0.97 32.5 15.3 4.32 0.18 412 11.2 1.2 Example 4 0.41 18.2 13.7 0.88 0.32 1060 18.5 2.3 Example 5 1.23 29.4 9.8 1.22 0.28 223 8.5 / Example 6 0.27 7.3 3.78 0.40 0.45 875 15.3 1.1 Example 7 1.47 34.9 17.2 3.22 0.25 201 10.1 / Comparative Example 1 0.47 39.3 31.2 4.23 0.25 1405 28.8 3 Comparative Example 2 0.61 22.5 / / / 581 / / Comparative Example 3 2.1 39.3 / / / 105 / /

[0128] Remark:

[0129] The unit of inlet pore density ρ is: pores / 10000μm 2 .

[0130] Table 4. Morphological parameters of the cross-sections of PES filter membranes obtained in each embodiment and comparative example.

[0131] Pore ​​area ratio of mesoporous layer / % Average pore size of mesoporous layer / μm Gradient of average pore size variation in mesoporous layer Average diameter of supporting fibers / μm Aperture ratio Pre-filter layer thickness / μm Average pore size of pre-filter layer / μm Pre-filter layer pore area ratio / % Protective layer thickness / μm Example 1 17.4 1.67 0.11 0.58 2.88 77.1 2.74 33.9 14.2 Example 2 19.1 1.88 0.13 0.64 2.94 80.2 3.37 37.2 16.4 Example 3 20.8 2.01 0.09 0.75 2.68 68.9 3.08 35.4 12.1 Example 4 14.8 1.43 0.12 0.44 3.25 78.7 3.12 36.2 14.9 Example 5 22.1 2.66 0.09 0.61 4.36 88 4.34 43.2 / Example 6 10.3 0.81 0.08 0.23 3.52 62 1.23 27.9 13.4 Example 7 24.8 2.97 0.14 0.88 3.38 82.1 3.98 40.1 / Comparative Example 1 15.2 1.51 0.13 0.48 3.15 78.2 3.15 36.2 11.9 Comparative Example 2 18.5 1.72 0.12 0.65 2.65 76.9 2.74 32.8 13.9 Comparative Example 3 / / / / / 76.7 4.22 44.1 12.7

[0132] Remark:

[0133] The unit of the average pore size variation gradient of the mesoporous layer is μm / μm; the pore size ratio specifically refers to the ratio of the average pore size of the pores in the cross section of the mesoporous layer to the average diameter of the supporting fiber.

[0134] Table 5 Performance parameters of PES filter membranes prepared in each embodiment and comparative example

[0135] PMI average pore size / μm LRV Membrane flow rate / s <![CDATA[Loading amount / L / m 2 > Example 1 0.27 ＞7 10.25 4475.8 Example 2 0.24 ＞7 13.12 3578.9 Example 3 0.52 ＞4 8.79 3872.1 Example 4 0.25 ＞7 15.68 2783.4 Example 5 0.57 ＞4 9.93 3054.09 Example 6 0.16 ＞8 19.59 1433.5 Example 7 0.43 ＞5 10.72 2542.9 Comparative Example 1 0.26 ＞7 28.25 953.2 Comparative Example 2 0.29 ＞7 21.33 1321.8 Comparative Example 3 0.28 ＞7 38.85 536.8

[0136] in conclusion

[0137] 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 to achieve the desired bacterial filtration effect, depending on the actual needs. For example, the PES filter membrane of Example 3 has a relatively high average pore size (0.52 μm) and relatively poor bacterial retention capacity (LRV < 7). Therefore, in actual use, PES membranes can be stacked to maintain a high bacterial retention capacity. For example, two layers of PES filter membranes from Example 3 can be stacked, or, for example, a combination of the PES filter membrane from Example 3 and the PES filter membrane from Example 1 can be stacked.

[0138] By comparing Example 4 and Comparative Example 1, it can be found that the average pore diameter K and pore density of the inlet holes in Comparative Example 1 are slightly higher than those in Example 4, and the thickness of the pore layer in Comparative Example 1 is slightly lower than that in Example 4. The pore area ratio of the pore layer in Comparative Example 1 is slightly higher than that in Example 4. The expected result is that the number of effective flow channels and the effective flow channel area of ​​the inlet surface of the filter membrane in Comparative Example 1 are higher than those of the filter membrane in Example 4. The load capacity (dirt holding capacity) of the filter membrane in Comparative Example 1 is basically close to that of Example 4. However, in actual use, the flux and loading of Comparative Example 1 are much lower than those of Example 4. This may be because the pore area ratio (especially the pore area ratio of the main inlet hole) of Comparative Example 1 is too large, there are too many main inlet holes and the main inlet holes are too large, the non-uniformity of the inlet surface is too high, the non-solid part of the inlet surface is relatively large, and the pressure resistance of the porous body near the inlet surface cannot be guaranteed. Under high pressure, the pore structure deformation of the inlet surface and the porous body near the inlet surface is large, and the pore structure may even collapse. Once the pore structure is excessively deformed or even collapses, the flux and loading of the filter membrane will both decrease.

[0139] By comparing Example 1 and Comparative Example 2, it can be found that the average pore diameter K and pore density of the inlet holes in Comparative Example 2 are slightly higher than those in Example 1. Furthermore, the thickness and pore area ratio of the mesoporous layer in Comparative Example 2 and Example 1 are basically similar. The expected result is that the flux of Comparative Example 2 is slightly higher than that of Example 1, and the loading capacity of Comparative Example 2 is basically close to that of Example 1. However, in actual use, the flux and loading capacity of Comparative Example 2 are far lower than those of Example 4. This may be because the inlet surface of the filter membrane in Comparative Example 2 does not include the main inlet hole, and its inlet surface is too uniform. Large particles of impurities easily clog the inlet holes and form a filter cake, thus reducing both the overall flux and loading capacity of the filter membrane.

[0140] The filter membrane prepared in Comparative Example 3 consists only of a pre-filtration layer (macropore layer) and a separation layer (micropore layer), and is a typical V-shaped asymmetric filter membrane. In actual use, the flux and loading capacity of this filter membrane are very low. This may be because, for a two-layer filter membrane, the inlet surface is the side closest to the pre-filtration layer. Due to the large pore size of the pre-filtration layer, under high feed pressure (50 psi), the pore structure of the pre-filtration layer (especially for the porous body near the inlet surface) is prone to deformation or even collapse. Once the pore structure of the pre-filtration layer is deformed or collapses, both the ability to guide the feed (flux) and the dirt-holding capacity (loading capacity) will decrease significantly.

[0141] 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. A high-pressure-resistant PES filter membrane, comprising a porous body having non-directional tortuous pathways within the porous body, one side of the porous body being an inlet surface and the other side being an outlet surface, characterized in that, The porous body comprises, along its thickness direction, a mesoporous layer, a pre-filtration layer, and a separation layer in sequence. One side of the mesoporous layer is the liquid inlet surface. The SEM average pore size of the pre-filtration layer is larger than the SEM average pore size of the mesoporous layer. The average pore size of the filter membrane is 0.15-0.6 μm. The liquid inlet surface is provided with a plurality of liquid inlet holes, the average SEM pore size K of the liquid inlet holes is 0.2-1.5 μm, and the pore area ratio of the liquid inlet surface is 5-35%. The main inlet holes are those with a diameter of not less than 1.5K, and the pore area ratio of the main inlet holes on the inlet surface is 2-25%.

2. The high-pressure-resistant PES filter membrane according to claim 1, characterized in that, The inlet holes with a diameter not higher than 0.7K are secondary inlet holes, and the pore area ratio of the secondary inlet holes on the inlet surface is 0.4-5%.

3. The high-pressure-resistant PES filter membrane according to claim 2, characterized in that, The ratio of the number of main inlet holes to the number of secondary inlet holes is 0.25-0.

5.

4. The high-pressure-resistant PES filter membrane according to claim 1, characterized in that, The pore density ρ of the inlet holes on the inlet surface is 200-900 holes / 1000μm. 2 The number of main inlet holes accounts for 10-20% of the total number of inlet holes.

5. The high-pressure-resistant PES filter membrane according to claim 1, characterized in that, The inlet holes with a diameter of not less than 3K are considered extra-large inlet holes, and the number of extra-large inlet holes on the inlet surface accounts for 1-3% of the total number of inlet holes.

6. The high-pressure-resistant PES filter membrane according to claim 1, characterized in that, The thickness of the mesoporous layer is 8-20 μm, and the pore area ratio of the cross-section of the mesoporous layer is 10-25%.

7. The high-pressure-resistant PES filter membrane according to claim 1, characterized in that, The average SEM pore size of the mesoporous layer cross-section is 0.8-3 μm, and the average SEM pore size of the mesoporous layer gradually increases along the direction of liquid flow.

8. A high-pressure-resistant PES filter membrane according to claim 7, characterized in that, Along the flow direction of the liquid feed, the average pore size variation gradient of the mesoporous layer, measured by SEM, is 0.08-0.15 μm / μm.

9. A high-pressure-resistant PES filter membrane according to claim 1, characterized in that, The mesoporous layer includes supporting fibers, which are interconnected to form a three-dimensional network structure of the mesoporous layer. The SEM average diameter of the supporting fibers is 0.2-0.9 μm, and the ratio of the SEM average pore diameter of the mesoporous layer cross-section to the SEM average diameter of the supporting fibers is 2.5-4.

5.

10. A high-pressure-resistant PES filter membrane according to claim 1, characterized in that, The thickness of the pre-filter layer is 60-90μm, the average SEM pore size of the pre-filter layer cross-section is 1-5μm, and the pore area ratio of the pre-filter layer cross-section is 25%-45%.

11. A high-pressure-resistant PES filter membrane according to claim 1, characterized in that, The porous body includes a protective layer, the separation layer is located between the pre-filter layer and the protective layer, the SEM average pore size of the protective layer is larger than the SEM average pore size of the separation layer, and the thickness of the protective layer is 12-20 μm.

12. The preparation process of a high-pressure-resistant PES filter membrane according to any one of claims 1-11, 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: 20-50 parts of polyethersulfone resin, 50-80 parts of solvent and 10-25 parts of pore-forming agent; the casting solution temperature is 35-60℃. S2. Pretreatment: The carrier loaded with the liquid film is placed in a pretreatment bath for pretreatment for 5-15 seconds to obtain a pretreated membrane. The pretreatment bath includes a good pretreatment solvent and a non-pretreatment solvent, with the concentration of the good pretreatment solvent in the pretreatment bath being 45-65 wt%. S3. First-stage curing: The carrier loaded with the pretreated film is immersed in a pre-coagulation bath for phase separation and curing. After phase separation, a film is obtained. The pre-coagulation bath includes a good pre-coagulation solvent and a non-pre-coagulation solvent. The concentration of the non-pre-coagulation solvent in the pre-coagulation bath is 70~95wt%. The first-stage curing time is 5-20s. S4. Reprocessing: The carrier loaded with the biofilm is placed in a reprocessing bath for reprocessing for 5-25 seconds to obtain a reprocessed 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 80-95 wt%. S5. Secondary curing: The carrier loaded with the reprocessed film is immersed in a re-coagulation bath for phase separation and curing. After phase separation is completed, a film is obtained. The re-coagulation bath includes a non-solvent for re-coagulation. The secondary curing time is 40-80 seconds. S6, Post-processing; The membrane was washed with pure water and then dried to obtain the PES filter membrane.

13. The preparation process of a high-pressure-resistant PES filter membrane according to claim 12, characterized in that, In step S2, the temperature of the pretreatment bath is 1-10°C higher than the temperature of the casting solution, and in step S3, the temperature of the pre-coagulation bath is 10-20°C lower than the temperature of the casting solution.

14. The preparation process of a high-pressure-resistant PES filter membrane according to claim 13, characterized in that, The temperature difference between the pretreatment bath and the pre-coagulation bath is 10-25℃.

15. The preparation process of a high-pressure-resistant PES filter membrane according to claim 12, characterized in that, The recoagulation bath also includes a good recoagulation solvent, and the concentration of the non-solvent in the recoagulation bath is 80-95 wt%.

16. The preparation process of a high-pressure-resistant PES filter membrane according to claim 15, characterized in that, The casting solution solvent, pretreatment solvent, pre-solidification solvent, retreatment solvent, and re-solidification 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 pre-coagulation non-solvent, the retreatment non-solvent, and the re-coagulation 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.

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