Sulfone polymer hollow fiber ultrafiltration membrane, and preparation method and application thereof

Abstract

The application discloses a sulfone polymer hollow fiber ultrafiltration membrane and a preparation method and application thereof. The ultrafiltration membrane comprises a main body, the main body comprises an outer rejection layer, a finger-shaped hole layer and an inner rejection layer; a plurality of first holes with an SEM average pore diameter of 20-100 nm are arranged on the outer surface, the hole density of the first holes on the outer surface is not less than 10 / 25 mu m 2 ; the thickness of the outer rejection layer is not less than 5 mu m; a plurality of second holes with an SEM average pore diameter of not more than 400 nm are arranged on the inner surface, the thickness of the inner rejection layer is not less than 3 mu m; the ultrafiltration membrane has an ideal membrane structure, the first holes on the outer surface have a relatively large pore diameter, and the outer rejection layer is relatively thick; the membrane is relatively easy to clean, the cleanliness of the membrane is ensured, the flux attenuation is low, the service life is long, and the ultrafiltration membrane is particularly suitable for terminal filtration of ultrapure water; and the preparation method provided by the application can conveniently, quickly and effectively prepare the above sulfone polymer hollow fiber ultrafiltration membrane.

Description

Technical Field

[0001] This invention relates to the field of membrane materials technology, and more specifically to a sulfone polymer hollow fiber ultrafiltration membrane, its preparation method, and its application. Background Technology

[0002] Ultrapure water, also known as UP water, refers to water with a resistivity of 18 MΩ*cm (25℃). This type of water contains virtually no impurities other than water molecules, and is free of bacteria, viruses, dioxins, and other organic matter. It also lacks essential minerals and trace elements, essentially meaning it contains almost all atoms except oxygen and hydrogen. Ultrapure water can be used in the preparation of ultrapure materials (semiconductor components, nano-fine ceramic materials, etc.) through distillation, deionization, reverse osmosis, or other appropriate supercritical fine technologies. With the rapid development of the semiconductor industry, ultrapure water is essential for the production and assembly of components such as single-crystal silicon, semiconductor chips, and liquid crystal displays, leading to an ever-increasing demand for highly purified ultrapure water.

[0003] In the preparation of ultrapure water, modern processes mainly employ steps such as pretreatment, electrodialysis, ultraviolet sterilization, reverse osmosis, ion exchange, and ultrafiltration. For example, Chinese Patent Application No. CN201280074530X (Kurita Kogyo Co., Ltd.) "Ultrapure Water Manufacturing Apparatus" includes... Figure 1 The patent details each step in the preparation of ultrapure water, demonstrating how a well-designed reverse osmosis system achieves high-purity ultrapure water. However, a crucial (and final) step, besides reverse osmosis, is the removal of residual micro-impurities from the water using an ultrafiltration membrane. These micro-impurities negatively impact the practical application of the ultrapure water. These impurities are small (typically around 6K), making removal difficult, and requiring a rejection rate of over 90% for 6K impurities. Even a small leakage of impurities renders the ultrapure water useless. To achieve high rejection efficiency, the ultrafiltration membranes used by those skilled in the art have very small pore sizes on their outer surface (often below 10nm), significantly smaller than the particle size of these micro-impurities. This allows for the sieving mechanism to trap these micro-impurities near the outer surface, resulting in high-purity ultrapure water. However, research has revealed that ultrafiltration membranes with very small pore sizes also present certain problems.

[0004] ① Cleaning before leaving the factory is very difficult. During the cleaning process, many impurities on the membrane itself are difficult to remove. Therefore, a large amount of cleaning solution is needed to clean for a long time to remove the impurities. This is time-consuming and labor-intensive, greatly extending the product delivery cycle. Moreover, the cleaning solution is usually ultrapure water, resulting in significant economic losses.

[0005] ② During the ultrafiltration process, tiny impurities in the ultrapure water to be purified can easily clog the pores on the outer surface of the membrane, leading to a rapid decline in membrane flux and making it impossible to produce ultrapure water quickly over a long period of time; moreover, the dirt-holding capacity is low, affecting the service life.

[0006] The aforementioned problems with existing ultrafiltration membranes have affected the preparation of ultrapure water, and consequently, its widespread application. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a sulfone polymer hollow fiber ultrafiltration membrane, its preparation method, and its application. This ultrafiltration membrane has an ideal membrane structure with relatively large pores on its outer surface and a thick outer retention layer. While ensuring high retention efficiency, the membrane itself is relatively easy to clean, ensuring its own cleanliness. It also has low flux attenuation and a long service life, making it particularly suitable for terminal filtration of ultrapure water.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a sulfone polymer hollow fiber ultrafiltration membrane, comprising a body, one side of which is an inner surface facing the inner lumen, and the other side of which is an outer surface. In the direction from the outer surface to the inner surface, the body sequentially comprises an outer retention layer, a finger-shaped pore layer, and an inner retention layer; one side of the outer retention layer is the outer surface; one side of the inner retention layer is the inner surface; both the outer and inner retention layers have non-directional tortuous pathways; the finger-shaped pore layer has a plurality of finger-shaped pores distributed circumferentially and extending radially along the membrane.

[0009] The outer surface has a plurality of first holes, the average SEM pore size of the first holes is 20-100 nm, and the pore density of the first holes on the outer surface is not less than 10 holes / 25 μm. 2 The outer retaining layer has a thickness of not less than 5 μm; the inner surface has a plurality of second pores, the average SEM pore size of the second pores is not higher than 400 nm, and the thickness of the inner retaining layer is not less than 3 μm.

[0010] In ultrapure water terminal filtration, a key indicator of the ultrafiltration membrane is its retention efficiency. In this invention, the membrane is a 6K ultrafiltration membrane, requiring a retention efficiency of no less than 90% for impurities with a molecular weight of 6K. This means ensuring that there are virtually no impurity particles in the ultrapure water, as even a small amount of impurity particles can significantly impact the various applications of ultrapure water. According to existing technology, ultrafiltration primarily achieves separation and retention through sieving. To ensure the retention efficiency of the ultrafiltration membrane, those skilled in the art typically adjust the pore size of the membrane surface to make it very small, often below 10 nm, generally much smaller than the particle size of tiny impurities (the membrane pore size is often one-tenth the particle size of the impurity). The pore size (even smaller) allows the membrane to trap various minute impurities near its outer surface through a sieving mechanism, thereby obtaining ultrapure water with high purity. However, defects of varying sizes are inevitable during membrane fabrication. Even very small defects (invisible to the naked eye) can affect the membrane's retention efficiency. Therefore, those skilled in the art typically only make the pore size on the outer surface of the membrane smaller and smaller, as this is the only way to ensure the corresponding retention efficiency from a conventional perspective. It is impossible to adjust the pore size by making it slightly larger, because if the pores are slightly larger, those skilled in the art generally consider that the ultrafiltration membrane cannot meet the high retention efficiency requirement and is not practical. The value of this approach (therefore willing to spend a lot of time cleaning the membrane fibers to ensure their cleanliness) is a technological bias. However, continuous research has revealed that this perception is a technological prejudice. This invention utilizes a first pore with a slightly larger diameter on the outer surface (the average SEM pore size of the first pore is 20-100 nm), combined with a relatively thick outer retention layer (the thickness of the outer retention layer is not less than 5 μm) and tortuous pathways within the outer retention layer. These features work together to ensure that this ultrafiltration membrane has good retention efficiency. Furthermore, to further improve retention efficiency (on the one hand, to minimize the impact of membrane fabrication defects on retention efficiency, and on the other hand, for some special applications...), In ultrafiltration (where higher retention efficiency is required), this invention further regulates the pore size of the second pore on the inner surface to ensure it is not too large. Preferably, the SEM average pore size of the second pore is not higher than 400 nm. At the same time, the inner retention layer also has a certain thickness (not less than 3 μm). With the synergistic effect of the second pore with a certain pore size, the inner retention layer with a certain thickness, and the tortuous pathway of the inner retention layer, it further plays a supplementary retention role, thereby ensuring that the ultrafiltration membrane has a high retention efficiency for tiny impurities in ultrapure water, which is beneficial for producing ultrapure water with high purity. This ultrafiltration membrane design overcomes the corresponding technical biases and is therefore innovative.

[0011] Meanwhile, since the membrane pores on the first outer surface of this invention are relatively large, various problems caused by small pores on the outer surface can be avoided. Most importantly, the cleanliness of the membrane itself is greatly improved, and cleaning before leaving the factory is relatively easy (cleaning efficiency is greatly improved). During the cleaning process, impurities in the membrane itself are easily removed. Therefore, it is not necessary to use a large amount of cleaning solution for a long time. Only a relatively small amount of cleaning solution is needed to remove the impurities in the membrane itself in a relatively short time, saving time and effort, increasing production efficiency, and greatly improving economic benefits. (In the semiconductor field, the cleanliness of the membrane fibers themselves is also very important, far exceeding that in other fields. It is desirable to avoid contaminating ultrapure water with impurities contained in the membrane fibers.)

[0012] Furthermore, in existing technologies, if the pore size of the first pore on the outer surface is very small, the number of first pores on the outer surface of the membrane is easily reduced (within a certain range, the number of membrane pores is directly proportional to the pore size; the smaller the pore size, the fewer the number of membrane pores). Therefore, during ultrafiltration, tiny impurities in the ultrapure water can easily clog the pores (first pores) on the outer surface of the membrane, leading to a rapid decline in membrane flux and a significantly reduced lifespan; simultaneously, the overall dirt-holding capacity of the membrane is low. In contrast, the pore size of the first pore on the outer surface of this invention is larger, and after adjustment, the pore density reaches no less than 10 pores / 25μm. 2 The outer surface has an appropriate number of primary pores (not too few), which ensures that tiny impurities in ultrapure water are not easily clogged by the membrane pores, resulting in a slower overall flux decay of the membrane and the ability to maintain a high flux for a long time, quickly producing ultrapure water with high purity. It is worth noting that the pore density is combined with the application of ultrapure water. Since there are not many impurities in ultrapure water during ultrafiltration, an excessive number of primary pores is not required. This number of primary pores is sufficient to meet the needs of practical applications, and it also helps the outer surface to obtain good pressure resistance.

[0013] Furthermore, the main body of this invention sequentially comprises an outer retention layer, a finger-shaped pore layer, and an inner retention layer (i.e., the finger-shaped pore layer is located between the outer retention layer and the inner retention layer); one side of the outer retention layer is the outer surface (the outer retention layer plays the main role in retaining minute impurities); one side of the inner retention layer is the inner surface (the inner retention layer plays the auxiliary role in retaining minute impurities), and the finger-shaped pore layer has several finger-shaped pores distributed along the circumference of the membrane and extending along the radial direction of the membrane. The presence of the finger-shaped pore structure greatly improves the overall porosity of the membrane, thereby facilitating the membrane to obtain a higher flux and producing ultrapure water with high purity in a shorter time.

[0014] It should be noted that, in this invention, the non-directional tortuous path refers to a randomly oriented groove structure and / or a discretely distributed pore structure, and each non-directional tortuous path is interconnected. During filtration, the liquid flows within the tortuous pore structure, and impurities in the liquid are intercepted through sieving, adsorption, and other methods, which is beneficial for the full interception of impurities. The outer interception layer has a certain thickness and corresponding tortuous paths, which makes it easy to intercept various tiny impurities.

[0015] In summary, the ultrafiltration membrane of this invention has large pores on its outer surface and a thick outer retention layer, thus ensuring high retention while being relatively easy to clean, maintaining its own cleanliness, and exhibiting low flux attenuation and a long service life. Furthermore, the inner surface has pores of suitable size and an inner retention layer of a certain thickness, further improving the retention efficiency. In addition to the outer and inner retention layers, the ultrafiltration membrane also has a finger-like pore layer with large pores, ensuring good flux and making it particularly suitable for terminal filtration of ultrapure water.

[0016] Furthermore, the ultrafiltration membrane of the present invention is integrally formed, meaning that the entire structure of the membrane fibers is made of the same material and is formed directly during the membrane preparation process; in the transition from the membrane thickness direction, there is only a change in the membrane structure, which is an asymmetric membrane; in contrast, for example, composite membranes have a multi-layer structure, which is made by applying a dense layer, which serves as the retention layer, onto a porous layer or porous membrane, often a microporous support layer or support membrane, in a separate process step; the materials constituting the support layer and the retention layer in a composite membrane are often different; the integrally formed porous membrane has higher mechanical strength than the composite membrane and has almost no risk of delamination.

[0017] In this invention, the SEM average pore size and pore density of the first pore on the outer surface of the filter membrane, as well as the SEM average pore size and pore density of the second pore on the inner surface, can be characterized by scanning electron microscopy (SEM) of the membrane structure, followed by measurement and calculation using computer software (such as Matlab, NIS-Elements, etc.) or manually. During membrane fabrication, the pore size and pore distribution are generally uniform and consistent in the direction perpendicular to the membrane thickness (planar if the membrane is a flat sheet, and perpendicular to the radius if it is a hollow fiber membrane). Therefore, the overall pore size and pore area ratio on a given plane can be reflected by the pore size and pore area ratio in a specific region. In actual measurement, the inner and outer surfaces of the membrane can be characterized using an electron microscope to obtain corresponding SEM images. Since the pore size and pore distribution on the inner and outer surfaces are generally uniform, a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 100μm 2(10μm x 10μm) or, the specific area size depends on the actual situation. Then, use appropriate computer software or manual measurement to determine the size and number of membrane pores on that area, perform several tests, and take the average value to obtain the average pore size and pore density of membrane pores on the inner and outer surfaces of the membrane by SEM. Of course, those skilled in the art can also obtain the above parameters by other measurement methods. The above measurement methods are for reference only.

[0018] In this invention, the first and second holes may have two morphologies when observed by SEM: one is a relatively regular circular hole, and the other is a hole similar to an ellipse. The SEM average hole diameter claimed in this invention specifically refers to the diameter of the relatively regular circular hole and the length of the minor axis of the hole similar to an ellipse.

[0019] As a further improvement of the present invention, the average SEM pore size of the first hole is 30-80 nm, and the pore density of the first hole on the outer surface is 15-50 holes / 25 μm. 2 The first water contact angle of the outer surface is 40°-85°, preferably 45°-70°.

[0020] To ensure the effective retention of various minute impurities in water by the ultrafiltration membrane, the SEM average pore size of the first pore is preferably 30-80 nm. This more suitable pore size helps to fully retain impurities (the outer retention layer is the most critical area for impurity retention inside the membrane, so appropriately adjusting the size of the outer surface membrane pores can further ensure the retention efficiency). On the other hand, it also ensures the cleanliness of the membrane fibers themselves, as impurities inside the membrane are relatively easy to be cleaned out by the cleaning solution, and have little impact on the overall flux of the membrane.

[0021] Meanwhile, the pore density of the first hole on the outer surface is 15-50 holes / 25μm. 2The outer surface of the membrane has a suitable number of first pores, which ensures that tiny impurities in ultrapure water do not easily clog the membrane pores, thus resulting in a slower decline in the overall membrane flux. On the other hand, in ultrapure water filtration (external pressure filtration), the outer surface, as the inlet surface and the pressure-bearing surface, needs to have higher pressure resistance (i.e., collapse strength). This is especially important for such high-precision retention; (if the pressure resistance is not high, the membrane pores will either deform during the ultrafiltration process, affecting the retention efficiency, or collapse, affecting the flux). At the same time, since ultrapure water is already relatively clean at the end of filtration, the number of tiny impurities it contains is not large, so a large number of membrane pores is not required. In other words, the pore size and number of the first pores on the outer surface of the membrane in this invention are closely related to ultrapure water applications and are quite unique. In this invention, by having a suitable pore size and a suitable number of first pores on the outer surface of the filter membrane, the retention efficiency is ensured while also having good mechanical strength (collapse strength), with minimal impact on membrane flux and a slower decline in membrane flux, making it particularly suitable for use in ultrapure water end filtration.

[0022] Research has shown that during the separation process of ultrafiltration membranes, not only does the pore size of the membrane play a role in separation, but also some properties of the membrane's outer surface (such as roughness and surface energy) affect the retention efficiency to varying degrees. The first water contact angle can reflect certain properties of the membrane surface to a certain extent. Research has found that when the first water contact angle is 40°-85°, preferably 45°-70°, it indicates that the ultrafiltration membrane has good hydrophilicity, allowing ultrapure water to quickly wet the membrane fibers for filtration. On the other hand, it further affects the membrane's retention efficiency, ensuring that the membrane has a high retention efficiency and fully captures various impurities in the ultrapure water. In this invention, the first water contact angle refers to the regular contact angle formed when 10-100 microliters of water droplets are uniformly applied to the material surface instantaneously (within 0.4s) using a contact angle meter with water as the test liquid.

[0023] As a further improvement of the present invention, the SEM average pore size of the second hole is 40-300 nm, and the pore density of the second hole on the inner surface is 10-45 pores / 4 μm. 2 .

[0024] The ultrapure water filtration of this invention is an external pressure filtration, meaning the fluid first passes through the outer surface, then the inner surface, and finally flows out. Therefore, the membrane pores on the inner surface do not need to be very small; preferably, the SEM average pore size of the second pore is 40-300 nm (preferably slightly larger than the pore size of the first pore on the outer surface). On the one hand, under the combined effect of a certain thickness (mainly the thickness of the inner retention layer) and a tortuous path, the slightly larger inner surface membrane pores (second pores) can play a supplementary retention role, further ensuring retention efficiency, while also giving the membrane a good overall flux. Furthermore, if the membrane pores on the inner surface are too small, it will affect the overall cleaning difficulty of the membrane (impurities near the inner surface of the membrane fibers are difficult to clean), and it will also easily cause rapid clogging of the second pores, affecting service life and reducing the overall flux of the membrane, thus slowing down the filtration speed of the ultrapure water. On the other hand, when the inner surface membrane pores are too large, they cannot play a retention role, easily leading to a low overall retention efficiency of the membrane. Furthermore, the pore density of the second pores on the inner surface is 10-45 pores / 4μm. 2 That is, the inner surface has a suitable number of second holes. With the second holes having a suitable pore size, the overall flux of the membrane is guaranteed to be high on the one hand, and the pressure resistance of the inner surface of the membrane is high (the membrane burst strength is high), which facilitates various processing.

[0025] As a further improvement of the present invention, the ratio of the SEM average aperture of the second hole to the SEM average aperture of the first hole is 1.2-5:1; and / or,

[0026] The average pore size variation gradient of the ultrafiltration membrane is 0.08-0.8 nm / μm;

[0027] The average pore size variation gradient of the ultrafiltration membrane is calculated as follows: (SEM average pore size of the second pore - SEM average pore size of the first pore) / thickness of the ultrafiltration membrane.

[0028] In existing technologies, ultrafiltration membranes typically have very small pore sizes on their outer surface (i.e., the diameter of the first pore) to ensure retention efficiency. However, very small pore sizes can lead to low overall porosity, resulting in low overall membrane flux. To prevent excessively low flux in existing ultrafiltration membranes, the pore sizes on the inner surface (i.e., the diameter of the second pore) are generally larger, ensuring that the overall membrane flux meets the requirements of practical applications. However, this membrane structure presents the following problems: ① The larger pore size on the inner surface reduces the compressive strength of the inner surface. ① The pore size is not high; ② The difference between the pore sizes on the inner and outer surfaces of the membrane is large, resulting in a large variation in the overall pore size of the membrane, which leads to low overall mechanical strength (tensile strength and elongation at break) of the membrane, affecting the practical application range; In this invention, since the pore size of the first hole on the outer surface is relatively large, the difference between the pore sizes on the inner and outer surfaces of the membrane is not large. After research, it is preferred that the ratio of the average SEM pore size of the second hole to the average SEM pore size of the first hole is 1.2-5:1. At this ratio, the membrane not only has good retention efficiency and flux, but also good tensile strength and elongation at break.

[0029] Since the membrane pore size changes with membrane thickness, this invention further uses the magnitude of the average pore size change gradient to reflect the rate of change of membrane pore size with thickness. A larger value indicates a faster pore size change, and a smaller value indicates a smaller pore size change. This value can be obtained by subtracting the average SEM pore size of the first pore from the average SEM pore size of the second pore, and then dividing by the thickness of the ultrafiltration membrane. Therefore, the unit is nm (representing pore size) / 1 μm (representing thickness). In this invention, the average pore size change gradient of the ultrafiltration membrane is 0.08-0.8 nm / μm. This relatively small gradient indicates that the membrane pore size change is not too rapid, and there are neither excessively large nor excessively small pores. This ensures that the membrane as a whole has good mechanical strength and pressure resistance, and is not easily damaged under high pressure. Furthermore, it ensures efficient membrane retention, effectively capturing various minute impurities in ultrapure water. The ultrafiltration membrane also has a high flux and a large dirt-holding capacity.

[0030] As a further improvement of the present invention, on the outer surface, some adjacent first holes are separated by first fibers; the SEM average length of the first fibers is 50-200 nm; the SEM average width of the first fibers is 10-70 nm.

[0031] The outer retention layer is a crucial area within the membrane matrix for retaining minute impurities in ultrapure water. The outer surface is the first point of direct contact between the outer retention layer and the ultrapure water phase to be purified. Therefore, the stability of the pore size of the first pore on the outer surface significantly impacts the stability of the retention efficiency. If the first pore collapses or shrinks during filtration, the membrane's retention efficiency decreases, making it unable to efficiently produce high-purity ultrapure water for extended periods, resulting in a shorter lifespan. Furthermore, in this invention, the first pores are relatively large, and the number of first pores is relatively high (the pore area ratio of the outer surface of the membrane in this invention is higher than that of existing membranes). Therefore, under prolonged filtration at high pressure, the pore size of the first pores on the outer surface is likely to deform, affecting the retention efficiency and flux. Research has shown that a first fiber is used to separate some adjacent first pores. The first fiber provides support to the first pore, ensuring its stability and enabling long-term, efficient retention of various minute impurities in the water. It also further enhances the pressure resistance of the outer surface. Furthermore, the preferred SEM average length of the first fiber is 50-200 nm, and the average SEM width is 10-70 nm. With the first fiber of this length and width working in conjunction with the appropriate number and size of first pores on the outer surface, it can stably and efficiently retain various impurities in ultrapure water for a long time, resulting in highly purified ultrapure water. Simultaneously, it gives the outer surface of the membrane high pressure resistance (collapse strength), facilitating various processing of the membrane fibers, expanding its application range, and enabling the membrane to have a large flux for rapid filtration of ultrapure water (if the first fiber is too coarse, the membrane flux may decrease, and the filtration speed may slow down).

[0032] As a further improvement of the present invention, on the inner surface, some adjacent second holes are separated by a second fiber; the SEM average length of the second fiber is 60-400 nm; the SEM average width of the second fiber is 15-95 nm.

[0033] The inner retention layer further supplements the area for retaining minute impurities in ultrapure water. The inner surface is the last part of the membrane to come into contact with the ultrapure water fluid, i.e., the outlet surface. Therefore, the stability of the pore size of the second pore on the outer surface has a certain impact on the stability of the retention efficiency, and also affects the overall membrane flux. This is because if the first pore collapses or shrinks during filtration, it will reduce the retention efficiency and pose a risk of leakage of minute impurities, especially in special circumstances such as a sudden power outage, further increasing the risk of leakage and potentially resulting in ultrapure water that does not meet practical application requirements. Furthermore, it will reduce the overall membrane flux because the pore area ratio on the inner surface is relatively higher than that on the outer surface, making the impact on flux more significant. Additionally, the pore size of the second pore is also larger, making it more prone to deformation during long-term filtration. This invention utilizes partial phase... The second pores are separated by second fibers; the second fibers provide support for the second pores, thus ensuring their stability and reducing the possibility of impurity leakage over a long period, ensuring that the membrane can maintain a high flux for an extended period, while also further improving the pressure resistance of the inner surface; furthermore, the SEM average length of the second fibers is preferably 60-400 nm; the SEM average width of the second fibers is 15-95 nm. With the second fibers of such length and width working in conjunction with the appropriate number and size of second pores on the inner surface, it can, on the one hand, supplement the retention function and further improve the retention efficiency, and on the other hand, enable the membrane to have high flux and quickly filter ultrapure water (if the second fibers are too thick, the membrane flux may be reduced and the filtration speed may be slower), and also give the inner surface of the membrane high pressure resistance (burst strength), which is beneficial for various processing of the membrane fibers and has a wide range of applications;

[0034] At the same time, the combined action of the first and second fibers ensures that the membrane as a whole has good mechanical strength, namely high tensile strength and high elongation at break.

[0035] As a further improvement of the present invention, the thickness of the outer retention layer is 15-120 μm, and is 5%-50% of the film thickness; the thickness of the inner retention layer is 10-80 μm.

[0036] The outer retention layer is a crucial area for trapping various minute impurities in ultrapure water. Most minute impurities are trapped in this layer, therefore, it needs a certain thickness. Insufficient thickness significantly reduces the membrane's retention efficiency and capacity (i.e., shortens its lifespan), failing to meet practical application requirements. In this invention, the first pore on the outer surface has a relatively large pore size, necessitating a relatively thick outer retention layer to ensure retention efficiency. Research has shown that the outer retention layer thickness is 15-120 μm. This thickness, combined with the appropriately sized first pore on the outer surface, effectively captures various minute impurities in ultrapure water, facilitating the production of highly purified ultrapure water. Simultaneously, because the outer retention layer has relatively low porosity (compared to finger-like pores), this thickness better ensures the overall mechanical strength of the membrane. Furthermore, the pores within the outer retention layer have relatively small pore sizes, and the porosity in this region is relatively low. The thickness of the outer retention layer is crucial. When the outer retention layer is too thick, and / or its proportion of the overall membrane thickness is too large, the overall membrane flux will decrease significantly. Conversely, when the proportion of the outer retention layer to the overall membrane thickness is too small, it will affect the retention efficiency. Research indicates that the thickness of the outer retention layer should be 5%-50% of the membrane thickness, preferably 10%-45% of the overall membrane thickness, thus ensuring both high retention efficiency and high flux. The inner retention layer is designed to further guarantee the ultrafiltration membrane's retention efficiency, ensuring high retention efficiency. Therefore, the inner retention layer also needs a certain thickness (it cannot be too thin). Furthermore, although the pores on the inner surface are slightly larger than those on the outer surface, the pore size of the inner retention layer is still relatively small, resulting in lower porosity. Therefore, the inner retention layer cannot be too thick, otherwise the overall membrane flux will decrease significantly. Research indicates that the thickness of the inner retention layer is preferably 10-80 μm. This further ensures that the membrane has high retention efficiency, high flux, and excellent mechanical strength.

[0037] In this invention, the thickness of the outer retention layer and the thickness of the inner retention layer can be obtained by characterizing the morphology of the membrane cross-section using a scanning electron microscope, then selecting a certain area and measuring it using computer software (such as Matlab, NIS-Elements, etc.) or manually, and taking the average value to further calculate the corresponding thickness value; of course, it is understood that those skilled in the art can also obtain the above parameters through other measurement methods.

[0038] As a further improvement of the present invention, the ratio of the thickness of the outer retention layer to the thickness of the inner retention layer is 0.6-3:1, preferably 1-2.5:1; the sum of the thickness of the outer retention layer and the thickness of the inner retention layer is 30%-70% of the thickness of the ultrafiltration membrane, preferably 40%-60%.

[0039] In this invention, both the outer and inner retention layers are regions capable of retaining minute impurities in ultrapure water. Compared to the finger-shaped pore layer, the pore diameters in these two regions are smaller, and the porosity is also lower, making them relatively dense. If the thickness difference between these two regions is too large, it will lead to a large deviation in the uniformity of various strengths of the membrane, which will easily result in various defects. Therefore, after research, the ratio of the thickness of the outer retention layer to the thickness of the inner retention layer is controlled at 0.6-3:1 (the thickness difference between the two regions is not large), thereby ensuring the uniformity of various strengths of the membrane, and thus ensuring that the membrane has stable retention efficiency and flux over a long period of time. Since the outer retention layer is the key region for impurity retention, while the inner retention layer is a supplementary region for retention, in order to ensure retention efficiency, we preferably select that the thickness of the outer retention layer is not less than the thickness of the inner retention layer (the ratio of the two is preferably 1-2.5:1), which is more conducive to the membrane obtaining high retention efficiency and minimizing the leakage of minute impurities.

[0040] Compared to the finger-like pore layer region, the outer and inner retention layers are relatively dense with relatively low porosity. To ensure the overall porosity of the membrane and thus achieve good flux, the sum of the outer and inner retention layer thicknesses should not be too large, and conversely, to ensure overall membrane strength, the sum should not be too small. Research has shown that the sum of the outer and inner retention layer thicknesses should be controlled to be 30%-70% of the ultrafiltration membrane thickness, preferably 40%-60%. This ratio, combined with the finger-like pore structure...

[0041] This is more conducive to ensuring that the membrane has good flux, and on the other hand, it has good strength, which can ensure that the structure of the finger pore layer is hardly affected during long-term filtration.

[0042] As a further improvement of the present invention, the outer retention layer has outer retention fibers for forming a porous structure, and the SEM average diameter of the outer retention fibers is 25-75 nm; the inner retention layer has inner retention fibers for forming a porous structure, and the SEM average diameter of the inner retention fibers is 15-70 nm.

[0043] The outer retention layer is a crucial area for retaining various minute impurities in ultrapure water. Most minute impurities are retained in this layer; therefore, if the pores within the outer retention layer collapse or shrink, it will significantly impact the overall retention efficiency of the membrane. Furthermore, in practical applications, the market desires ultrafiltration membranes with a long service life, ideally exceeding five years. To ensure consistently high retention efficiency over the long term, the membrane pores within the outer retention layer must remain relatively stable. This necessitates appropriately fine outer retention fibers. If the fibers are too fine, the stability of the membrane pores within the outer retention layer cannot be guaranteed, affecting pore size and porosity. The structure is easily affected by external forces, resulting in a shorter service life. Research has found that the average SEM diameter of the external retention fiber is 25-75nm. Under the action of external retention fibers of this thickness, on the one hand, it can support the membrane pores inside the external retention layer, preventing collapse or shrinkage during filtration. That is, the external retention layer can stably and efficiently retain various tiny impurities for a long time. On the other hand, it also gives the external retention layer an ideal pore structure, which is conducive to the membrane to obtain high flux (excessively thick external retention fibers will have a certain impact on membrane flux). Ultimately, it has a longer service life, generally more than 5 years.

[0044] The inner retention layer is a supplementary area used to retain various minute impurities in ultrapure water, playing a role in further supplementing and retaining impurities. At the same time, in order to minimize the leakage of minute impurities, the inner retention fiber of appropriate thickness is required to ensure the stability of the internal pore structure of the inner retention layer. Studies have shown that the average diameter of the inner retention fiber on SEM is 15-70nm. With the help of inner retention fiber of this thickness, it can support the membrane pore structure inside the inner retention layer, preventing collapse or shrinkage during the filtration process. In other words, the inner retention layer can effectively retain various minute impurities for a long time, reducing the risk of impurity leakage.

[0045] Furthermore, the synergistic effect of appropriate external retention fibers and appropriate external retention layer thickness is conducive to the membrane having good collapse strength, while the synergistic effect of appropriate internal retention fibers and appropriate internal retention layer thickness is conducive to good burst strength. At the same time, it was unexpectedly found that when the membrane has these characteristics, the overall tensile strength and elongation at break of the membrane are both high, which can ensure the stability of flux and retention efficiency over a long period of time.

[0046] In this invention, the SEM average diameter and other characteristics of the externally and internally retained fibers can be obtained by characterizing the membrane cross-section using a scanning electron microscope, then selecting a certain area and measuring it using computer software (such as Matlab, NIS-Elements, etc.) or manually to obtain the diameter of the externally and internally retained fibers, taking the average value, and then further calculating the corresponding SEM average diameter. Of course, it is understood that those skilled in the art can also obtain the above parameters through other measurement methods.

[0047] As a further improvement of the present invention, the ratio of the average SEM diameter of the externally retained fiber to the average SEM diameter of the internally retained fiber is 0.8-2; the ratio of the average SEM diameter of the externally retained fiber to the average SEM pore size of the first hole is not less than 0.4; and the ratio of the average SEM diameter of the internally retained fiber to the average SEM pore size of the second hole is not less than 0.3.

[0048] The outer retaining fibers are used to maintain the stability of the pore structure within the outer retaining layer, and the inner retaining fibers are used to maintain the stability of the pore structure within the inner retaining layer. Compared to the finger-like pore layer, the outer and inner retaining layers are relatively dense, and the thicknesses of the two regions are preferably similar. Therefore, the diameters of the outer and inner retaining fibers are also preferably similar. Studies have shown that the ratio of the average SEM diameter of the outer retaining fibers to the average SEM diameter of the inner retaining fibers is 0.8-2, which is more conducive to ensuring higher overall tensile strength and elongation at break of the membrane (i.e., no easily broken areas in the membrane fibers), and greatly reduces the processing difficulty. The outer surface is part of the outer retaining layer, and research has found that the thickness of the outer retaining fibers also affects the stability of the membrane pores on the outer surface. To mitigate the impact of the membrane's internal structure, it is preferable that the ratio of the SEM average diameter of the outer retaining fibers to the SEM average pore size of the first pore is not less than 0.4. This further ensures the stability of the first pore, thereby further guaranteeing the stability of the membrane's retention efficiency. This allows for the long-term high-efficiency retention of various minute impurities, resulting in ultrapure water with high purity. The inner surface is part of the inner retaining layer. Research has shown that the thickness of the inner retaining fibers also affects the stability of the membrane pores on the inner surface. Preferably, the ratio of the SEM average diameter of the inner retaining fibers to the SEM average pore size of the second pore is not less than 0.3. This further ensures the stability of the second pore, thereby further reducing impurity leakage and ensuring the membrane has excellent retention efficiency and flux.

[0049] As a further improvement of the present invention, the extension direction of the long axis of the finger-shaped pores is the radial direction of the filter membrane, and the extension direction of the short axis of the finger-shaped pores is the circumferential direction of the filter membrane; the SEM average long axis of the finger-shaped pores is 60-200μm; the ratio of the SEM average long axis of the finger-shaped pores to its SEM average short axis is 3-13:1.

[0050] The ratio of the average major diameter of the finger-shaped apertures to the thickness of the outer intercepted layer is 1.5-4.

[0051] Since both the outer and inner retention layers can trap minute impurities in ultrapure water, the pore size and porosity in these regions are relatively small. To ensure a high overall porosity and thus a high flux, the membrane body of this invention also includes a finger-shaped pore layer. This layer contains multiple finger-shaped pores (i.e., the cross-sectional structure of the ultrafiltration membrane is preferably a single-finger-shaped pore structure; the finger-shaped pores are finger-like holes with high internal porosity). The long axis of the finger-shaped pores extends in the direction of the membrane fiber diameter. When the long axis is too large, it indicates that the pores in that region are too large, causing the internal pores to collapse easily when fluid passes through that region, resulting in the membrane fiber not being able to function properly. Normal use is not possible; however, it can also lead to low overall mechanical strength of the membrane, greatly increasing the difficulty of processing the membrane fibers into components and reducing its practicality; if its length diameter is too small, the overall flux of the membrane will still be small, failing to meet the needs of actual use; after research, the average length diameter of the finger pores in SEM is 60-200μm, which on the one hand ensures a high overall flux of the membrane, enabling rapid filtration of ultrapure water, and on the other hand has little impact on the mechanical strength of the membrane, so that the membrane still has good mechanical strength; the reason why the ultrafiltration membrane of this invention has a single finger pore structure is based on continuous structural optimization of the outer and inner retention layers under the premise of having appropriate thickness, which is quite special;

[0052] Furthermore, besides the major axis of the finger pores affecting membrane flux and mechanical strength, the minor axis of the finger pores also influences membrane flux and mechanical strength to some extent. Research has shown that by adjusting the ratio of the SEM average major axis to the SEM average minor axis of the finger pores to 3-13:1, the finger pores possess a suitable minor axis, and the ratio of major to minor axis is within an appropriate range. This further ensures high membrane flux, allowing fluid to pass through the membrane body in a shorter time. Simultaneously, it further ensures high overall membrane mechanical strength, with the pore structure within the finger pore layer remaining largely unchanged during long-term filtration. Additionally, fiber analysis revealed that when the ratio of the SEM average major axis of the finger pores to the thickness of the outer retaining layer is 1.5-4, the outer retaining layer provides some support to the finger pore layer, further ensuring the stability of the internal pores of the finger pores.

[0053] As a further improvement of the present invention, the average SEM length of the distance between two adjacent finger-shaped apertures is 3-15 μm; the ratio of the average SEM length of the distance between two adjacent finger-shaped apertures to the average SEM minor diameter of the finger-shaped apertures is 1:1.5-6.

[0054] Finger pores are regions with relatively high porosity within the finger pore layer. The regions between adjacent finger pores are regions with relatively low porosity within the finger pore layer. Therefore, these regions need to have a suitable distance (defined by both absolute and relative values). Preferably, the average SEM length of the distance between two adjacent finger pores is 3-15 μm. The ratio of the average SEM length of the distance between two adjacent finger pores to the average SEM minor axis of the finger pores is 1:1.5-6, thus ensuring that the membrane fibers have suitable tensile strength and providing good support for the finger pores (especially in the circumferential direction of the membrane).

[0055] As a further improvement of the present invention, the molecular weight cutoff of the ultrafiltration membrane is 6K; the water flux of the ultrafiltration membrane is not less than 450 L*h. -1 *m -2 @0.1MPa; the porosity of the ultrafiltration membrane is 40%-85%, and the thickness is 150-350μm.

[0056] The ultrafiltration membrane of this invention has an outer retention layer, a finger-like pore layer, and an inner retention layer, which gives the membrane a good overall porosity of 40%-85%, thereby further ensuring that the membrane fibers have a high flux and can filter ultrapure water quickly, ensuring the preparation of high-purity ultrapure water in a short time. Commonly used porosity testing methods include mercury intrusion porosimetry, density method, and wet-dry membrane weighing method. Of course, those skilled in the art can also obtain the above parameters through other measurement methods, and the above measurement methods are for reference only.

[0057] The membrane thickness can be determined by characterizing the membrane structure using a scanning electron microscope, followed by calculation using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement. When the membrane thickness is too small, its mechanical strength will be low, and the filtration time will be too short, resulting in ineffective filtration. When the membrane thickness is too large, the filtration time will be too long, leading to excessive time costs. In this invention, to ensure retention efficiency, the outer and inner retention layers need to have relatively thick thicknesses. At the same time, to achieve a high overall porosity, the finger-shaped pore layer also needs to have a certain thickness.

[0058] After comprehensive consideration, the thickness of the filter membrane of the present invention is 150-350μm, which is relatively large. This ensures that the membrane not only has high mechanical strength, but also can effectively filter and has high retention efficiency, while also having good flux.

[0059] Retention tests revealed that the ultrafiltration membrane has a molecular weight cutoff of 6K (with a retention efficiency of over 90% for 6K impurities), exhibiting very high retention efficiency. This makes it particularly suitable for terminal filtration of ultrapure water, resulting in highly purified ultrapure water. Water flux tests showed that the membrane's water flux is no less than 450 L / h.-1 *m -2 @0.1MPa, with a relatively large flux, meaning the filter membrane has a good filtration speed, it can produce a large volume of high-purity ultrapure water in a short time, resulting in high economic benefits.

[0060] As a further improvement of the present invention, the tensile strength of the ultrafiltration membrane is 3-8 MPa, and the elongation is 40%-70%; the burst strength of the ultrafiltration membrane is greater than 13 kgf / cm². 2 The collapse strength is greater than 7 kgf / cm 2 ;

[0061] The ultrafiltration membrane exhibits TOC precipitation ≤0.5 ppb and metal ion precipitation ≤10 ppt.

[0062] The tensile strength and elongation at break are important indicators for evaluating the mechanical strength of a filter membrane. Under certain conditions, the greater the tensile strength of the membrane, the better its mechanical strength. Tensile strength refers to the membrane's ability to withstand parallel tensile forces. During testing, the membrane sample is subjected to a tensile load until it breaks. Based on the maximum tensile load at failure and the change in the membrane sample's dimensions (length), the tensile strength and elongation at break can be calculated. Both tensile strength and elongation at break can be measured using a universal tensile testing machine. The testing method for tensile strength is well-known in the field; for example, ASTM D790 or ISO 178 details the procedure for tensile strength testing. In this invention, the filter membrane exhibits a tensile strength greater than 2 MPa and an elongation at break of 40%-70%. This indicates that the ultrafiltration membrane of this invention has good tensile strength and elongation at break, demonstrating good mechanical properties, high industrial practical value, and fully meeting market demands. Furthermore, internal and external pressure strength tests were conducted, revealing that the burst strength of the ultrafiltration membrane is greater than 13 kgf / cm². 2 (Obtained from internal pressure test), collapse strength greater than 7 kgf / cm² 2 (Obtained from external pressure testing) All strengths are high, greatly reducing the difficulty of the process and ensuring that it can be processed in various ways. In addition, because the first pore size on the outer surface of the ultrafiltration membrane of this invention is relatively large, its own impurities are easily cleaned, greatly reducing the cleaning difficulty, saving time and effort. At the same time, after cleaning, its own cleanliness is very high, with TOC precipitation ≤0.5ppb and metal ion precipitation ≤10 ppt, ensuring that no impurities are introduced during long-term filtration, which is more conducive to obtaining ultrapure water with high cleanliness.

[0063] Furthermore, the present invention also provides a method for preparing a sulfone polymer hollow fiber ultrafiltration membrane, comprising the following steps:

[0064] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 10-25 parts of sulfone polymer, 5-15 parts of pore-forming agent, 50-90 parts of first organic solvent and 1-5 parts of water;

[0065] The sulfone polymer is at least one of polyethersulfone, polysulfone, and polyphenylsulfone;

[0066] The core fluid comprises a second organic solvent and water; the water content in the core fluid is 30%-50%.

[0067] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head;

[0068] Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, wherein the length of the air section is 10-30cm and the temperature is 20-40℃;

[0069] Step 4: Pre-gelling: The molded article is placed in a first gel bath for pre-gelling for 30-60 seconds; the first gel bath includes a third organic solvent and water; the water content in the first gel bath is 30%-60%;

[0070] Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 5-20 seconds. The second gel bath is water.

[0071] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane.

[0072] As a further improvement of the present invention, the pore-forming agent is at least one of polyethylene glycol, polypropylene glycol and polyvinyl alcohol, and the number average molecular weight of the pore-forming agent is 1500-5000; the first organic solvent, the second organic solvent and the third organic solvent are all at least one of dimethyl sulfoxide, dimethylformamide, N-ethylpyrrolidone, dimethylacetamide, N-methylpyrrolidone and N,N-diethylformamide.

[0073] As a further improvement of the present invention, the humidity of the air section is not greater than 20%; the temperature of the air section is 10-30°C lower than the temperature of the casting solution.

[0074] As a further improvement of the present invention, the temperature of the first gel bath is 5-15°C lower than the temperature of the casting solution.

[0075] The temperature of the second gel bath is 40-80℃; the spinning speed is 5-20m / min.

[0076] In preparing the sulfone polymer hollow fiber ultrafiltration membrane of the present invention, a casting solution is first prepared. The casting solution includes a sulfone polymer (at least one of polyethersulfone, polysulfone, and polyphenylsulfone) as the membrane-forming substance, an organic solvent (used to dissolve the sulfone polymer, the organic solvent being at least one of dimethyl sulfoxide, dimethylformamide, N-ethylpyrrolidone, dimethylacetamide, N-methylpyrrolidone, and N,N-diethylformamide), a pore-forming agent, and water. As one of the key points of the present invention, the composition of the casting solution is quite special. First, a small amount of water is added to the casting solution (generally, water is not added to casting solutions). Water is currently the most common non-solvent. Through continuous research, it has been found that adding a small amount of water to the casting solution can appropriately adjust the phase separation rate. Under the combined effect of subsequent instantaneous phase separation, it is easy to obtain an ideal single-finger pore structure, which is beneficial for obtaining a high-flux ultrafiltration membrane. Of course, the water content cannot be too high. If too much water is added, it will cause… The phase separation rate is too fast, which prevents the formation of relatively large first pores on the outer surface, and the number of first pores on the outer surface will be too small. In addition, an appropriate amount of pore-forming agent is added. The pore-forming agent is at least one of polyethylene glycol, polypropylene glycol and polyvinyl alcohol, and the number average molecular weight of the pore-forming agent is 1500-5000. The addition of the pore-forming agent is more conducive to the formation of pores, such as forming an ideal number of pores on the inner and outer surfaces of the membrane, thereby ensuring the overall porosity of the membrane. However, the molecular weight of the pore-forming agent cannot be too high. If it is too high, it will be difficult to clean out, thus affecting the cleanliness of the membrane fibers themselves. At the same time, the content of each component in the casting solution is controlled to ensure the formation of an ideal casting solution. The formulation of the casting solution will have a significant impact on the structure and performance of the final ultrafiltration membrane, such as affecting the pore size and fiber thickness of the filter membrane. This ensures that the final filter membrane has an ideal membrane pore structure and fiber thickness, and can then be used for terminal ultrapure water filtration.

[0077] Furthermore, the core used in the extrusion of the hollow fiber membrane in this invention is in liquid form, thus requiring the selection of a suitable core liquid. The core liquid includes an organic solvent and water (water is a non-solvent), with the organic solvent preferably being the organic solvent in the casting solution, although other solvents capable of dissolving the membrane-forming substances can also be used. By selecting a suitable core liquid (the corresponding substances and their proportions), on the one hand, the pressure inside the hollow fiber membrane cavity can be kept in balance with the external pressure, thereby stabilizing the cavity of the hollow fiber membrane and ensuring that the wall thickness of the hollow fiber membrane is basically the same. On the other hand, the core liquid also affects the pore size and pore size distribution of the inner surface. Under the combined effect of the casting solution formulation and coagulation bath conditions, by controlling various conditions in the membrane phase separation process, a filter membrane with an ideal inner surface pore structure (i.e., having a certain pore size and a certain number of second pores on the inner surface) can be manufactured.

[0078] The second step is spinning: the casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the molded product is a hollow fiber membrane; the extruded hollow fiber membrane has a surface facing the cavity, i.e., the inner surface, and a surface opposite to the cavity, i.e., the outer surface.

[0079] In ultrapure water terminal filtration, a crucial performance characteristic is retention efficiency. Existing technologies, to ensure this efficiency, often make the pore size on the outer surface of the membrane very small. However, in this invention, to achieve a suitable pore size (slightly larger) and a suitable number of primary pores on the outer surface, the molded product is pretreated in an air section. This air section is 10-30 cm long and at a temperature of 20-40°C. Combined with the appropriate casting solution, this facilitates phase separation on the outer surface of the molded product, resulting in an ideal pore structure. Preferably, the humidity in the air section is no greater than 20%, and the air temperature is 10-30°C lower than the casting solution temperature. This further ensures a suitable phase separation rate on the outer surface of the molded product, ultimately resulting in more uniform pore size and a larger number of primary pores (compared to ultrapure water terminal filtration).

[0080] Because the pores on the outer surface of the membrane in this invention are slightly larger, a thicker outer retention layer is needed to ensure retention efficiency. After the molded product undergoes pretreatment, a pregeling process is performed. The phase separation rate at this stage cannot be too fast, as this would result in an overly dense pore structure within the outer retention layer, while a slow rate would lead to an overly porous structure. Therefore, a suitable first gel bath and a suitable pregeling time are required. Research indicates that the pregeling time is 30-60 seconds. The first gel bath includes a third organic solvent and water. The water content in the first gel bath is 30%-60% (this is by mass; for example, 5g of water and 5g of the third organic solvent result in a water content of 50%). Based on the pretreatment, by gelling and separating the phases under the action of this first gel bath for a certain period, a suitable number and size of first pores with a relatively thick outer retention layer are ensured on the outer surface of the membrane, thereby ensuring the overall retention efficiency of the membrane and facilitating cleaning, thus guaranteeing the cleanliness of the membrane fibers themselves.

[0081] Next, transient phase separation is performed: the pre-gelled molded product is placed in the second gel bath for transient phase separation to form a raw membrane, with a phase separation time of 5-20 seconds; the second gel bath is water; after transient phase separation, a finger-like pore layer structure is formed, with finger-like pores of a certain length and width, thereby ensuring that the membrane has high porosity, which is conducive to obtaining high flux; finally, the raw membrane is washed in water to further remove organic solvents and other substances contained in the membrane fibers, and finally dried (natural drying or other drying methods can be selected) to finally obtain a hollow fiber ultrafiltration membrane.

[0082] Preferably, the temperature of the first gel bath is 5-15℃ lower than that of the casting solution, and the temperature of the second gel bath is 40-80℃. Under these temperatures, combined with the appropriate casting solution formulation and the dual-bath effect, ideal pore size and pore area ratio are achieved on both the inner and outer surfaces. This further ensures the membrane's retention efficiency while also giving it good flux and excellent mechanical strength. Preferably, the spinning speed is 5-20 m / min, and combined with the appropriate casting solution and air section pretreatment, the membrane as a whole will not have particularly small or large pores (fewer defects), thus ensuring that the filter membrane has both high retention efficiency and good flux, while also having high slump strength and burst strength.

[0083] As a further improvement of the present invention, an application of a sulfone polymer hollow fiber ultrafiltration membrane is provided, wherein the ultrafiltration membrane is used for terminal filtration in the preparation of ultrapure water.

[0084] The beneficial effects of this invention are as follows: The sulfone polymer hollow fiber ultrafiltration membrane provided by this invention comprises a main body, which includes an outer retention layer, a finger-shaped pore layer, and an inner retention layer; one side of the outer retention layer is the outer surface; one side of the inner retention layer is the inner surface; both the outer and inner retention layers have non-directional tortuous pathways; the finger-shaped pore layer has a plurality of finger-shaped pores distributed along the circumference of the membrane and extending radially along the membrane; the outer surface has a plurality of first pores, the SEM average pore size of the first pores is 20-100 nm, and the pore density of the first pores on the outer surface is not less than 10 pores / 25 μm. 2 The outer retention layer has a thickness of not less than 5 μm; the inner surface has several second pores, the average SEM pore size of the second pores is not higher than 400 nm, and the thickness of the inner retention layer is not less than 3 μm. This ultrafiltration membrane has an ideal membrane structure, with relatively large pores on its outer surface and a thick outer retention layer. While ensuring high retention efficiency (greater than 90% retention efficiency for 6K small molecules), the membrane itself is relatively easy to clean, ensuring its own cleanliness. It also has low flux decay and a long service life, making it particularly suitable for terminal filtration of ultrapure water. Attached Figure Description

[0085] Figure 1 A scanning electron microscope (SEM) image of the overall cross-section of the ultrafiltration membrane was prepared for Example 2, with a magnification of 50×.

[0086] Figure 2 The image shown is a scanning electron microscope (SEM) image of the outer retention layer in the ultrafiltration membrane prepared in Example 2, with a magnification of 20K×.

[0087] Figure 3 The image shows a scanning electron microscope (SEM) image of the inner retention layer in the ultrafiltration membrane prepared in Example 2, with a magnification of 20K×.

[0088] Figure 4 The image shows a scanning electron microscope (SEM) image of the outer surface of the ultrafiltration membrane prepared in Example 3, with a magnification of 20K×.

[0089] Figure 5 The image shown is a scanning electron microscope (SEM) image of the inner surface of the ultrafiltration membrane prepared in Example 3, with a magnification of 10K×. Detailed Implementation

[0090] To more clearly illustrate the overall concept of this application, detailed descriptions are provided below using embodiments. Unless otherwise specified, the raw materials and equipment used to prepare the filter membrane in the following embodiments are commercially available. Specifically, a Hitachi S-5500 scanning electron microscope was used to characterize the structural morphology of the filter membrane.

[0091] Example 1

[0092] A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane includes the following steps:

[0093] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 16 parts of sulfone polymer, 11 parts of pore-forming agent, 70 parts of first organic solvent, and 2 parts of water; the sulfone polymer is polysulfone; the core solution comprises a second organic solvent and water; the water content in the core solution is 40%; the pore-forming agent is polyethylene glycol; both the first and second organic solvents are N,N-diethylformamide; the casting solution temperature is 50℃.

[0094] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the spinning speed is 10m / min;

[0095] Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, wherein the air section is 20cm long, the temperature is 30℃, and the humidity of the air section is 10%.

[0096] Step 4: Pre-gelling: The molded article is placed in the first gelling bath for pre-gelling for 45 seconds; the first gelling bath includes a third organic solvent and water; the water content in the first gelling bath is 45%.

[0097] The temperature of the first gel bath is 10°C lower than that of the casting solution; the third organic solvent is N,N-diethylformamide.

[0098] Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 10 seconds. The second gel bath is water. The temperature of the second gel bath is 60°C.

[0099] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane. Example 2

[0100] A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane includes the following steps:

[0101] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 18 parts of sulfone polymer, 12 parts of pore-forming agent, 75 parts of first organic solvent and 3 parts of water; the sulfone polymer is polysulfone;

[0102] The core fluid comprises a second organic solvent and water; the water content in the core fluid is 40%; the pore-forming agent is polyethylene glycol;

[0103] The first and second organic solvents are dimethyl sulfoxide; the casting solution temperature is 47°C.

[0104] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the spinning speed is 10m / min;

[0105] Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, wherein the air section is 18cm long, the temperature is 27℃, and the humidity of the air section is 10%.

[0106] Step 4: Pre-gelling: The molded article is placed in a first gel bath for pre-gelling for 40 seconds; the first gel bath includes a third organic solvent and water; the water content in the first gel bath is 50%; the third organic solvent is dimethyl sulfoxide; the temperature of the first gel bath is 10°C lower than the casting solution temperature.

[0107] Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 20 seconds. The second gel bath is water. The temperature of the second gel bath is 70°C.

[0108] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane. Example 3

[0109] A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane includes the following steps:

[0110] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 20 parts of sulfone polymer, 13 parts of pore-forming agent, 80 parts of first organic solvent and 4 parts of water; the sulfone polymer is polyphenylsulfone;

[0111] The core fluid comprises a second organic solvent and water; the water content in the core fluid is 45%; the pore-forming agent is polypropylene glycol;

[0112] Both the first and second organic solvents are dimethylformamide; the casting solution temperature is 54°C.

[0113] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the spinning speed is 15m / min;

[0114] Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, wherein the air section is 15cm long, the temperature is 24℃, and the humidity is 15%.

[0115] Step 4: Pre-gelling: The molded article is placed in a first gel bath for pre-gelling for 35 seconds; the first gel bath includes a third organic solvent and water; the water content in the first gel bath is 55%; the third organic solvent is dimethylformamide; the temperature of the first gel bath is 15°C lower than the casting solution temperature.

[0116] Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 15 seconds. The second gel bath is water. The temperature of the second gel bath is 75°C.

[0117] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane. Example 4

[0118] A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane includes the following steps:

[0119] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 14 parts of sulfone polymer, 8 parts of pore-forming agent, 65 parts of first organic solvent and 1 part of water; the sulfone polymer is polyethersulfone; the core solution comprises a second organic solvent and water; the water content in the core solution is 35%; the pore-forming agent is polypropylene glycol;

[0120] Both the first and second organic solvents are dimethylacetamide; the casting solution temperature is 45°C.

[0121] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the spinning speed is 5 m / min;

[0122] Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, wherein the air section is 25cm long, the temperature is 35℃, and the humidity of the air section is 5%.

[0123] Step 4: Pre-gelling: The molded product is placed in the first gelling bath for pre-gelling for 54 seconds; the first gelling bath includes a third organic solvent and water; the water content in the first gelling bath is 40%; the third organic solvent is dimethylacetamide; the temperature of the first gelling bath is 5°C lower than the casting solution temperature.

[0124] Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 6 seconds. The second gel bath is water. The temperature of the second gel bath is 45°C.

[0125] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane. Example 5

[0126] A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane includes the following steps:

[0127] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 12 parts of sulfone polymer, 6 parts of pore-forming agent, 55 parts of first organic solvent and 1 part of water; the sulfone polymer is polyethersulfone; the core solution comprises a second organic solvent and water; the water content in the core solution is 30%; the pore-forming agent is polyvinyl alcohol;

[0128] Both the first and second organic solvents are N-ethylpyrrolidone; the casting solution temperature is 46°C.

[0129] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the spinning speed is 2m / min;

[0130] Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, the length of which is 30cm, the temperature is 40℃, and the humidity of the air section is 5%.

[0131] Step 4: Pre-gelling: The molded product is placed in the first gelling bath for pre-gelling for 60 seconds; the first gelling bath includes a third organic solvent and water; the water content in the first gelling bath is 35%; the third organic solvent is N-ethylpyrrolidone; the temperature of the first gelling bath is 4°C lower than the casting solution temperature.

[0132] Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 8 seconds. The second gel bath is water. The temperature of the second gel bath is 55°C.

[0133] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane. Example 6

[0134] A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane includes the following steps:

[0135] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 24 parts of sulfone polymer, 15 parts of pore-forming agent, 85 parts of first organic solvent, and 5 parts of water; the sulfone polymer is polyphenylene sulfone; the core solution comprises a second organic solvent and water; the water content in the core solution is 50%; the pore-forming agent is polyvinyl alcohol;

[0136] Both the first and second organic solvents are N-methylpyrrolidone; the casting solution temperature is 50°C.

[0137] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the spinning speed is 15m / min;

[0138] Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, the length of which is 12cm, the temperature is 20℃, and the humidity of the air section is 21%.

[0139] Step 4: Pre-gelling: The molded product is placed in the first gel bath for pre-gelling for 30 seconds; the first gel bath includes a third organic solvent and water; the water content in the first gel bath is 60%; the third organic solvent is N-methylpyrrolidone; the temperature of the first gel bath is 18°C ​​lower than the casting solution temperature.

[0140] Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 6 seconds. The second gel bath is water. The temperature of the second gel bath is 35°C.

[0141] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane. Comparative Example 1

[0142] A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane includes the following steps:

[0143] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 24 parts of sulfone polymer, 15 parts of pore-forming agent, 85 parts of first organic solvent and 5 parts of water; the sulfone polymer is polyphenylene sulfone; the core solution comprises a second organic solvent and water; the water content in the core solution is 50%; the pore-forming agent is polyvinyl alcohol;

[0144] Both the first and second organic solvents are N-methylpyrrolidone; the casting solution temperature is 50°C.

[0145] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the spinning speed is 15m / min;

[0146] Step 5: Instantaneous phase separation: The molded product is placed in a gel bath for instantaneous phase separation to form a film. The phase separation time is 6 seconds. The gel bath is water. The temperature of the second gel bath is 50°C.

[0147] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane.

[0148] Because the molded product extruded from the die undergoes instantaneous phase separation during the membrane fabrication process (i.e., without pretreatment and pregelation), the resulting ultrafiltration membrane has very small pore size and a low number of pores on its outer surface, resulting in a low overall porosity. This makes the ultrafiltration membrane difficult to clean, requiring a large amount of cleaning agent and a lengthy rinsing process, which is time-consuming and labor-intensive. Furthermore, it reduces the membrane's flux, making it unable to filter ultrapure water quickly. During filtration, the membrane pores are prone to clogging, leading to a rapid decrease in flux and significantly reducing the membrane's lifespan.

[0149] Comparative Example 2

[0150] A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane includes the following steps:

[0151] Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 24 parts of sulfone polymer, 15 parts of pore-forming agent, and 85 parts of first organic solvent; the sulfone polymer is polyphenylene sulfone; the core solution comprises a second organic solvent and water; the water content in the core solution is 50%; the pore-forming agent is polyvinyl alcohol;

[0152] Both the first and second organic solvents are N-methylpyrrolidone; the casting solution temperature is 50°C.

[0153] Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; the spinning speed is 10m / min;

[0154] Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, the length of which is 50cm, the temperature is 45℃, and the humidity of the air section is 5%.

[0155] Step 4: Pre-gelling: The molded product is placed in the first gelling bath for pre-gelling for 80 seconds; the first gelling bath includes a third organic solvent and water; the water content in the first gelling bath is 20%; the third organic solvent is N-methylpyrrolidone; the temperature of the first gelling bath is 2°C lower than the casting solution temperature.

[0156] Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 30 seconds. The second gel bath is water. The temperature of the second gel bath is 50°C.

[0157] Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane.

[0158] Because no water was added to the formulation during the membrane fabrication process, and the phase separation rate during pretreatment and pregelation was too slow, the pore size of the outer surface of the ultrafiltration membrane was too large. As a result, the ultrafiltration membrane produced in this way had too low retention efficiency for 6K small molecule impurities, and could not produce ultrapure water with high purity, thus having no practical value.

[0159] 1. Structural Characterization

[0160] The morphology of the PES hollow fiber membranes obtained in each embodiment was characterized using scanning electron microscopy, and the required data were then obtained; the specific results are shown in the table below:

[0161] Table 1:

[0162] SEM average pore size of the first hole (nm) <![CDATA[Hole density of the first hole / (holes / 25μm 2 )]]> Second hole SEM average pore size (nm) <![CDATA[Hole density of the second hole / (holes / 4μm 2 )]]> Example 1 60 30 180 28 Example 2 50 26 160 25 Example 3 40 22 120 22 Example 4 75 35 220 32 Example 5 85 44 250 36 Example 6 28 15 80 20 Comparative Example 1 10 2 30 5 Comparative Example 2 200 32 500 30

[0163] Table 2

[0164] SEM average length of the first fiber (nm) SEM average width of the first fiber (nm) SEM average length of the second fiber (nm) SEM average width of the second fiber (nm) Average pore size variation gradient (nm / μm) Example 1 130 40 250 50 0.48 Example 2 110 30 200 45 0.55 Example 3 90 25 150 35 0.40 Example 4 150 45 300 55 0.48 Example 5 180 55 350 65 0.55 Example 6 70 20 100 30 0.26

[0165] Table 3

[0166] First water contact angle of outer surface / ° Thickness of the outer retaining layer / μm Thickness of inner retaining layer / μm SEM average diameter of externally retained fibers (nm) SEM average diameter of internally retained fibers (nm) Example 1 55 60 40 50 45 Example 2 60 50 30 40 35 Example 3 65 35 25 35 30 Example 4 50 70 50 55 60 Example 5 44 85 60 60 70 Example 6 71 25 15 20 25 Comparative Example 1 89 5 2 5 10 Comparative Example 2 61 9 4 80 90

[0167] Table 4

[0168] SEM average major diameter of finger-shaped apertures / μm SEM average short diameter of finger-shaped apertures / μm SEM average length-to-short diameter ratio of finger-shaped apertures SEM average length of the distance between two adjacent finger-shaped apertures / μm Membrane porosity / % Film thickness / μm Example 1 150 20 7.5 8 65 250 Example 2 120 18 6.7 7 60 200 Example 3 140 16 8.8 5 55 200 Example 4 180 25 7.2 10 70 300 Example 5 155 30 5.2 14 75 300 Example 6 160 14 11.4 4 50 200 Comparative Example 1 197 10 19.7 2 20 200 Comparative Example 2 187 18 10.4 5 60 200

[0169] As shown in Tables 1-4, the hollow fiber ultrafiltration membranes prepared in Examples 1-6 of this invention are all integrally formed without any composite process, making the preparation process simple and suitable for large-scale application. Furthermore, the ultrafiltration membranes prepared in Examples 1-6 all have ideal membrane structures, with suitable pore sizes and pore areas on both the inner and outer surfaces, ensuring high-quality retention of various impurities. At the same time, since the first pore on the outer surface has a relatively large pore size, it is very easy to clean, ensuring the cleanliness of the membrane fibers themselves. They are particularly suitable for terminal filtration of ultrapure water.

[0170] Performance characteristics

[0171] Membrane flux is calculated as follows: The formula for calculating membrane flux (J) is: J = V / (T×A) Where:

[0172] J -- Membrane flux unit: L*h -1 *m -2

[0173] V -- Sampling volume (L); T -- Sampling time (h); A -- Effective membrane area (m²) 2 )

[0174] The operating conditions used for measuring the membrane separation performance in this invention are as follows: the feed liquid is deionized water, the operating pressure is 0.1 MPa, the operating temperature is 25°C, and the solution pH is 7.

[0175] Retention test: The retention efficiency of the filter membranes obtained for each example was tested, with the molecular weight of the retained substance being 6K;

[0176] <![CDATA[Flux L*h -1 *m -2 @0.1MPa]]> Retention efficiency Tensile strength / MPa Elongation at break / % Example 1 600 Greater than 95% 5.5 60 Example 2 580 Greater than 95% 6.5 55 Example 3 550 Greater than 95% 7 50 Example 4 620 Greater than 95% 5 65 Example 5 680 Greater than 95% 4 60 Example 6 480 Greater than 90% 6 50 Comparative Example 1 150 Greater than 90% 4 15 Comparative Example 2 500 20% 2 35

[0177] As shown in the table above, the hollow fiber ultrafiltration membranes prepared in Examples 1-6 of this invention have high flux and high retention efficiency, as well as good mechanical strength, making them particularly suitable for terminal filtration of ultrapure water. Furthermore, various leaching tests were conducted, revealing that TOC leaching was less than 0.5 ppb and metal ion precipitation was less than 1 ppt, indicating that the membrane fibers themselves are very clean and will not introduce new impurities, further ensuring the production of ultrapure water with high purity. Moreover, the membranes are easy to clean, requiring very little cleaning agent and a short cleaning time, resulting in high economic efficiency. Furthermore, burst strength and collapse strength tests were conducted, and we found that the burst strength of the ultrafiltration membranes prepared in Examples 1-6 is greater than 13 kgf / cm². 2 The collapse strength is greater than 7 kgf / cm 2 It has excellent performance and can be processed in various ways, greatly reducing the difficulty of processing.

[0178] 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 sulfone polymer hollow fiber ultrafiltration membrane, comprising a body, wherein one side of the body is an inner surface facing the inner lumen, and the other side of the body is an outer surface, characterized in that, In the direction from the outer surface to the inner surface, the main body sequentially includes an outer retention layer, a finger-shaped pore layer, and an inner retention layer; one side of the outer retention layer is the outer surface; One side of the inner retaining layer is the inner surface; Both the outer and inner retention layers have non-directional tortuous pathways; the finger-shaped pore layer has a number of finger-shaped pores distributed along the circumferential direction of the membrane and extending along the radial direction of the membrane; The outer surface has a plurality of first holes, the average SEM pore size of the first holes is 20-100 nm, and the pore density of the first holes on the outer surface is not less than 10 holes / 25 μm. 2 The thickness of the outer interception layer is not less than 5 μm; The inner surface has a plurality of second holes, the average SEM pore size of the second holes is not higher than 400 nm, and the thickness of the inner retaining layer is not less than 3 μm.

2. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The average SEM pore size of the first hole is 30-80 nm, and the pore density of the first hole on the outer surface is 15-50 pores / 25 μm. 2 The first water contact angle of the outer surface is 40°-85°.

3. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The average SEM pore size of the second pore is 40-300 nm, and the pore density on the inner surface of the second pore is 10-45 pores / 4 μm. 2 .

4. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The ratio of the average SEM aperture of the second hole to the average SEM aperture of the first hole is 1.2-5:1; And / or, The average pore size variation gradient of the ultrafiltration membrane is 0.08-0.8 nm / μm; The average pore size variation gradient of the ultrafiltration membrane is calculated as follows: (SEM average pore size of the second pore - SEM average pore size of the first pore) / thickness of the ultrafiltration membrane.

5. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, On the outer surface, some adjacent first holes are separated by first fibers; the average SEM length of the first fibers is 50-200 nm; the average SEM width of the first fibers is 10-70 nm.

6. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, On the inner surface, some adjacent second holes are separated by a second fiber; the SEM average length of the second fiber is 60-400 nm; the SEM average width of the second fiber is 15-95 nm.

7. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The outer retention layer has a thickness of 15-120 μm and accounts for 5%-50% of the membrane thickness; the inner retention layer has a thickness of 10-80 μm.

8. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The ratio of the thickness of the outer retention layer to the thickness of the inner retention layer is 0.6-3:1; the sum of the thicknesses of the outer retention layer and the inner retention layer is 30%-70% of the thickness of the ultrafiltration membrane.

9. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 8, characterized in that, The ratio of the thickness of the outer retention layer to the thickness of the inner retention layer is 1-2.5:

1.

10. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 8, characterized in that, The sum of the thickness of the outer retention layer and the thickness of the inner retention layer is 40%-60% of the thickness of the ultrafiltration membrane.

11. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The outer retaining layer contains outer retaining fibers for forming a porous structure, and the SEM average diameter of the outer retaining fibers is 25-75 nm. The inner retaining layer contains inner retaining fibers for forming a porous structure, and the SEM average diameter of the inner retaining fibers is 15-70 nm.

12. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 11, characterized in that, The ratio of the average SEM diameter of the externally retained fibers to the average SEM diameter of the internally retained fibers is 0.8-2. The ratio of the average SEM diameter of the externally retained fiber to the average SEM pore size of the first hole is not less than 0.4; The ratio of the average SEM diameter of the internally retained fiber to the average SEM pore size of the second hole is not less than 0.

3.

13. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The long axis of the finger-shaped pore extends in the radial direction of the filter membrane, and the short axis of the finger-shaped pore extends in the circumferential direction of the filter membrane. The SEM average major diameter of the finger-shaped aperture is 60-200 μm; the ratio of the SEM average major diameter of the finger-shaped aperture to its SEM average minor diameter is 3-13:

1. The ratio of the average major diameter of the finger-shaped apertures to the thickness of the outer intercepted layer is 1.5-4.

14. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The average SEM length of the distance between two adjacent finger-shaped apertures is 3-15 μm; The ratio of the average SEM length of the distance between two adjacent finger apertures to the average SEM minor diameter of the finger aperture is 1:1.5-6.

15. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The ultrafiltration membrane has a molecular weight cutoff of 6K; The water flux of the ultrafiltration membrane is not less than 450 L*h -1 *m -2 @0.1MPa; The ultrafiltration membrane has a porosity of 40%-85% and a thickness of 150-350 μm.

16. The sulfone polymer hollow fiber ultrafiltration membrane according to claim 1, characterized in that, The ultrafiltration membrane has a tensile strength of 3-8 MPa and an elongation of 40%-70%. The burst strength of the ultrafiltration membrane is greater than 13 kgf / cm². 2 The collapse strength is greater than 7 kgf / cm 2 ; The ultrafiltration membrane exhibits TOC precipitation ≤0.5 ppb and metal ion precipitation ≤10 ppt.

17. A method for preparing a sulfone polymer hollow fiber ultrafiltration membrane according to any one of claims 1 to 16, characterized in that, Includes the following steps: Step 1: Preparation of casting solution and core solution: The casting solution comprises the following components by weight: 10-25 parts of sulfone polymer, 5-15 parts of pore-forming agent, 50-90 parts of first organic solvent and 1-5 parts of water; The sulfone polymer is at least one of polyethersulfone, polysulfone, and polyphenylsulfone; The core fluid comprises a second organic solvent and water; the water content in the core fluid is 30%-50%. Step 2: Spinning: The casting solution and the core solution are extruded together from the die head, and the casting solution forms a molded product with an inner surface and an outer surface in the die head; Step 3: Pretreatment: The molded product is pretreated by passing it through an air section, wherein the length of the air section is 10-30cm and the temperature is 20-40℃; Step 4: Pre-gelling: The molded article is placed in a first gel bath for pre-gelling for 30-60 seconds; the first gel bath includes a third organic solvent and water; the water content in the first gel bath is 30%-60%; Step 5: Instantaneous phase separation: The pre-gelled molded product is placed in the second gel bath for instantaneous phase separation to form a film. The phase separation time is 5-20 seconds. The second gel bath is water. Step 6: Wash the raw membrane in water and dry it to obtain the ultrafiltration membrane.

18. The method for preparing a sulfone polymer hollow fiber ultrafiltration membrane according to claim 17, characterized in that, The pore-forming agent is at least one of polyethylene glycol, polypropylene glycol and polyvinyl alcohol, and the number average molecular weight of the pore-forming agent is 1500-5000. The first organic solvent, the second organic solvent, and the third organic solvent are all at least one of dimethyl sulfoxide, dimethylformamide, N-ethylpyrrolidone, dimethylacetamide, N-methylpyrrolidone, and N,N-diethylformamide.

19. The method for preparing a sulfone polymer hollow fiber ultrafiltration membrane according to claim 17, characterized in that, The humidity of the air section is no greater than 20%; the temperature of the air section is 10-30℃ lower than the temperature of the casting solution.

20. The method for preparing a sulfone polymer hollow fiber ultrafiltration membrane according to claim 17, characterized in that, The temperature of the first gel bath is 5-15°C lower than that of the casting solution; the temperature of the second gel bath is 40-80°C; and the spinning speed is 5-20 m / min.

21. The application of a sulfone polymer hollow fiber ultrafiltration membrane according to any one of claims 1 to 16, characterized in that, The ultrafiltration membrane is used for terminal filtration in the preparation of ultrapure water.

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