Moisture-permeable finger-hole hollow fiber membrane and method for producing the same

Abstract

The present application relates to the technical field of moisture permeable membrane materials, and provides a moisture permeable finger-shaped hole hollow fiber membrane and a preparation method thereof.The membrane body comprises a first finger-shaped hole layer and a second finger-shaped hole layer, and a support layer with a sponge-like porous structure is arranged between the first finger-shaped hole layer and the second finger-shaped hole layer; the first finger-shaped hole layer, the support layer and the second finger-shaped hole layer are connected in a transition mode by using continuous fibers; the first finger-shaped hole layer is provided with a plurality of first finger-shaped holes distributed along the circumference of the membrane; the second finger-shaped hole layer is provided with a plurality of second finger-shaped holes distributed along the circumference of the membrane; the average length-diameter of the first finger-shaped hole is not less than 30 μm; and the average length-diameter of the second finger-shaped hole is 10-30 μm longer than that of the first finger-shaped hole.The moisture permeable finger-shaped hole hollow fiber membrane provided in the present application has a high water vapor transmission rate and water conversion efficiency, while ensuring the mechanical strength of the hollow fiber membrane and prolonging the service life thereof.

Description

Technical Field

[0001] This invention relates to the field of moisture-permeable membrane materials technology, and in particular to a moisture-permeable finger-shaped hollow fiber membrane and its preparation method. Background Technology

[0002] Hollow fiber separation membranes include moisture-permeable hollow fiber membranes, which are mainly used in humidifiers. They generally have good hydrophilicity and selective permeability, separating water vapor in the air from other gas components. Water vapor is transferred from the side with high humidity to the side with low humidity through the membrane.

[0003] The water conversion efficiency of the membrane is closely related to the average pore size and porosity of the hollow fiber membrane. The larger the average pore size and the greater the porosity, the higher the water vapor permeation rate and the higher the water conversion efficiency of the hollow fiber membrane. However, as the average pore size of the membrane increases, the increase in porosity leads to a significant reduction in the mechanical strength of the membrane, thus reducing its service life.

[0004] Toray Industries, Inc. of Japan disclosed a water vapor permeable membrane in its 2009 patent CN102481524B, applicable to water vapor permeable membranes, hollow yarn membranes, and hollow yarn membrane assemblies for humidification devices in fuel cell systems. The membrane comprises adjacent dense layers and support layers. The dense layer has pores with a pore length of 0.1 μm or less and a thickness of 0.1 μm to 2 μm. The support layer has pores within 2 μm of the interface between the dense and support layers in the thickness direction, with the longest pore having a length of 0.3 μm or more. Additionally, the longest pore within 2 μm to 4 μm of the interface in the thickness direction has a length of 0.5 μm or more, with the length of the pores exceeding the length of the dense layer. It is known that the support layer has a single-layer finger-like pore structure. Due to the relatively long pore length of the single-layer finger-like pores, the membrane exhibits low mechanical strength.

[0005] Therefore, preparing a moisture-permeable hollow fiber membrane with high water conversion efficiency and strong mechanical properties is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] To address the aforementioned problems, this invention aims to provide a permeable finger-shaped hollow fiber membrane and its preparation method. This hollow fiber membrane exhibits high water vapor permeation rate and water conversion efficiency, while ensuring its mechanical strength and extending its service life.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A permeable hollow fiber membrane with finger-shaped pores includes a main body, one side of which is an inner surface and the other side is an outer surface. The main body has non-directional tortuous pathways. The main body comprises a first finger-shaped pore layer and a second finger-shaped pore layer. The first finger-shaped pore layer is located near the outer surface region of the main body, and the second finger-shaped pore layer is located near the inner surface region of the main body. The side of the second finger-shaped pore layer near the inner surface is a condensation layer for water vapor condensation, and one side of the condensation layer is the inner surface. A sponge-like porous support layer is located between the first finger-shaped pore layer and the second finger-shaped pore layer. The first finger-shaped pore layer, the support layer, and the second finger-shaped pore layer are connected by a continuous fiber transition; the first finger-shaped pore layer has a plurality of first finger-shaped pores distributed along the circumferential direction of the membrane, and the second finger-shaped pore layer has a plurality of second finger-shaped pores distributed along the circumferential direction of the membrane; the major axis extension direction of the first finger-shaped pores and the second finger-shaped pores is radial to the hollow fiber membrane, and the minor axis extension direction of the first finger-shaped pores and the second finger-shaped pores is circumferential to the hollow fiber membrane; the average major axis of the first finger-shaped pores is not less than 30 μm; the average major axis of the second finger-shaped pores is 10-30 μm longer than the average major axis of the first finger-shaped pores.

[0009] It should be noted that the non-directional tortuous pathways refer to irregularly oriented groove structures and / or discretely distributed pore structures, and all non-directional tortuous pathways are interconnected. "Continuous fiber connection" can be understood as the fibers between the protective layer, porous layer, and condensation layer being "integrated," existing in a continuous, integral connection without additional adhesive bonding. Unless torn by external force, the continuous fibers cannot be separated from each other. The first finger-like pore layer is the region of the main body near the outer surface with the first finger-like pores, where water vapor diffuses as a gas. The second finger-like pore layer is the region of the main body near the inner surface with the second finger-like pores. The support layer is the sponge-like network structure region located between the first and second finger-like pore layers, where water vapor diffuses as a gas. The condensation layer is the region where water vapor transforms from gas to liquid. A finger-like pore resembles the mark left by a pressed finger, with its longest inner diameter (i.e., major axis) oriented along the thickness direction of the hollow fiber membrane in the direction of water vapor permeation.

[0010] In this application, water vapor enters the first finger-shaped pore layer inside the membrane through the outer surface. Since the average major diameter of the first finger-shaped pores is not less than 30 μm, the water vapor has a low mass transfer resistance, which increases the water vapor permeation rate and allows a large amount of water vapor to enter the support layer. The water vapor accumulates in the support layer, creating a large concentration difference between the support layer and the second finger-shaped pore layer. This, in turn, promotes the flow of water vapor from the support layer into the second finger-shaped pore layer, increasing the driving force of the water vapor flow and accelerating the water vapor permeation rate. At the same time, the support layer between the first and second finger-shaped pore layers ensures the tensile strength and deformation resistance of the hollow fiber membrane, preventing the hollow fiber membrane from breaking or the pore structure from collapsing under external forces. Driven by the concentration gradient, water vapor flows to the second finger-shaped pore layer. The average major diameter of the second finger-shaped pore is 10-30 μm longer than that of the first finger-shaped pore. This prevents the first finger-shaped pore from being too long, resulting in an excessively fast water vapor permeation rate and excessive water vapor entering the support layer, which would block the flow channels and create concentration polarization, causing water vapor to flow back to the first finger-shaped pore layer. Simultaneously, it prevents the collapse of the pore structure near the outer surface of the hollow fiber membrane under external pressure. The longer average major diameter of the second finger-shaped pore ensures a relatively high water vapor permeation rate while increasing the water vapor flow path, preventing a large amount of water vapor from simultaneously reaching and accumulating in the condensation layer, thus blocking the flow channels and causing water vapor to flow back, reducing the water vapor permeation rate, and consequently reducing the water vapor conversion efficiency. In this application, a support layer is provided between the first and second finger-shaped pore layers, and the first and second finger-shaped pores have suitable average major diameters, ensuring the mechanical strength of the hollow fiber membrane while maintaining a high water vapor permeation rate and water conversion efficiency.

[0011] Furthermore, the average major diameter of the first finger-shaped aperture is 40-65 μm, and the ratio of the average major diameter of the first finger-shaped aperture to its average minor diameter is 5.5-7; the average major diameter of the second finger-shaped aperture is 60-85 μm, and the ratio of the average major diameter of the second finger-shaped aperture to its average minor diameter is 7.5-9.5.

[0012] It should be noted that the first and second finger-shaped holes are approximately elliptical in shape. The ratio of the major axis to the minor axis of the ellipse is the shape ratio. When the shape ratio is close to 1, both the major and minor axes of the ellipse need to bear a certain stress. It can be seen that when the shape ratio is greater than 1, the smaller the shape ratio, the greater the stress borne by the minor axis. That is, the pressure borne by the hollow fiber membrane is distributed at the major and minor axes to increase the deformation resistance of the hollow fiber membrane and prevent structural collapse. Therefore, in this application, the ratio of the average major axis to the average minor axis of the first and second finger-shaped holes can be regarded as the shape ratio. The shape ratio of the first finger-shaped hole is smaller than that of the second finger-shaped hole. It can be seen that when subjected to pressure, the minor axis of the first finger-shaped hole bears a larger stress, which can disperse the pressure and reduce the radial effect of the pressure on the hollow fiber membrane, making the deformation resistance of the hollow fiber membrane near the outer surface area stronger.

[0013] In this application, the average major diameter of the first finger-shaped pore is 40-65 μm, and the average major diameter of the second finger-shaped pore is 60-85 μm, which enables the hollow fiber membrane to have a higher water vapor permeation rate, thereby increasing the hydration efficiency. Moreover, the shape ratio of the first finger-shaped pore is smaller than that of the second finger-shaped pore, so the pressure borne by the first finger-shaped pore is more evenly distributed. The first finger-shaped pore plays a certain protective role for the second finger-shaped pore, reducing the radial effect of pressure on the hollow fiber membrane, effectively preventing the structural collapse of the hollow fiber membrane, making its structure more stable, and ensuring the mechanical strength of the hollow fiber membrane.

[0014] Furthermore, the average short diameter of the second finger-shaped aperture is 6.5-9.5 μm, and the ratio of the average short diameter of the second finger-shaped aperture to the average short diameter of the first finger-shaped aperture is 0.7-1.2.

[0015] In this application, the average short diameter of the second finger-shaped aperture has a suitable size, allowing water vapor to have a high permeation rate within the second finger-shaped aperture, thus preventing water vapor from stagnating in the support layer and reducing water conversion efficiency. Furthermore, the average short diameter of the second finger-shaped aperture has a suitable ratio to the average short diameter of the first finger-shaped aperture, ensuring a uniform diffusion rate of water vapor within the hollow fiber membrane. This allows water vapor to pass smoothly through the hollow fiber membrane, ensuring water conversion efficiency. It also prevents water vapor from diffusing too quickly within the first finger-shaped aperture, causing concentration polarization within the support layer and resulting in water vapor backflow, increasing mass transfer resistance within the first finger-shaped aperture. Alternatively, it prevents a sudden influx of large amounts of water vapor into the second finger-shaped aperture, where excessive water vapor cannot diffuse through the condensation layer to the outside of the membrane in time, easily causing water vapor backflow, increasing mass transfer resistance, reducing the water vapor permeation rate, and thus reducing water conversion efficiency.

[0016] Furthermore, the sum of the average major diameter of the first finger-shaped aperture and the average major diameter of the second finger-shaped aperture accounts for 60%-80% of the thickness of the hollow fiber membrane.

[0017] In this application, the sum of the average major diameters of the first and second finger-shaped pores accounts for 60%-80% of the thickness of the hollow fiber membrane. This increases the porosity of the hollow fiber membrane, giving it a higher water vapor permeation rate while maintaining its mechanical strength. This effectively prevents the hollow fiber membrane from collapsing due to pressure during operation. If the sum of the average major diameters of the first and second finger-shaped pores constitutes too large a proportion of the hollow fiber membrane, the mechanical strength is significantly reduced, thus greatly shortening its service life. Conversely, if the sum of the average major diameters of the first and second finger-shaped pores constitutes a small proportion, the water vapor permeation rate is reduced, thereby decreasing the water conversion efficiency of the hollow fiber membrane.

[0018] Furthermore, the distance between two adjacent first finger-shaped holes is a first distance, and the average length of the first distance is 2-6 μm; the distance between two adjacent second finger-shaped holes is a second distance, and the ratio of the average length of the second distance to the average length of the first distance is 0.1-0.5.

[0019] In this application, the average length of the first distance is 2-6 μm, which gives the first finger-shaped pore layer high mechanical strength, preventing structural collapse when the first finger-shaped pore layer is subjected to pressure, and at the same time protecting the second finger-shaped pore layer. In this application, the ratio of the average length of the second distance to the average length of the first distance is 0.1-0.5, that is, the average length of the second distance is less than the average length of the first distance. The pore density of the first finger-shaped pores in the first finger-shaped pore layer is less than the pore density of the second finger-shaped pores in the second finger-shaped pore layer. That is, the second finger-shaped pore layer has more flow channels, which makes the water vapor collected in the support layer uniformly dispersed in the flow channels of the second finger-shaped pores. This allows the water vapor in each flow channel of the second finger-shaped pore layer to pass through at a uniform speed, avoiding different water vapor permeation rates in each flow channel. This would prevent different water vapor flow velocities entering the condensation layer, increase the collision between water vapor and the pore wall, and thus increase the mass transfer resistance of the condensation layer. In this application, the average length of the second distance has a suitable ratio to the average length of the first distance, making the flow rate of water vapor within the hollow fiber membrane more uniform, avoiding collisions between water vapor particles or between water vapor and the pore walls, thus reducing the water vapor permeation rate and consequently decreasing the water conversion efficiency of the hollow fiber membrane. Here, pore density refers to the average number of pores per unit area of ​​the membrane cross-section.

[0020] Furthermore, the first finger-shaped hole has a plurality of first holes in its wall, with the diameter of the first hole near the support layer being larger than that of the first hole near the outer surface; the second finger-shaped hole has a plurality of second holes in its wall, with the diameter of the second hole near the support layer being larger than that of the second hole near the inner surface.

[0021] In this application, several non-directional, tortuous first flow channels exist between adjacent first finger-shaped holes. Some water vapor enters the first finger-shaped holes through these first flow channels and holes, and then enters the support layer through the first finger-shaped holes. As the length of the first flow channel increases, the amount of water vapor entering the channel also increases. The diameter of the first hole closer to the support layer is larger than that of the first hole closer to the outer surface, increasing the diffusion rate of water vapor within the first flow channel and preventing water vapor from accumulating and clogging the channel. This improves the diffusion rate of water vapor from the first flow channel to the first finger-shaped holes and increases the water conversion efficiency of the water vapor. Several non-directional, tortuous second flow channels exist between adjacent second finger-shaped holes, allowing water vapor from the support layer to surge into the second finger-shaped holes instantaneously in large quantities due to the concentration difference. Some water vapor within the second finger-shaped orifice enters the second flow channel through the second hole, effectively diverting the water vapor entering the second finger-shaped orifice layer. This prevents excessive water vapor from entering the condensation layer too quickly and clogging the pores, reducing the water vapor permeation rate, and consequently decreasing the water conversion efficiency. The diameter of the second hole closer to the support layer is larger than that of the second hole closer to the inner surface. When a large amount of water vapor enters the second hole, more water vapor enters the second flow channel through the larger diameter second hole, diverting the water vapor within the second finger-shaped orifice and preventing the instantaneous influx of water vapor from colliding and increasing mass transfer resistance.

[0022] Preferably, the average pore diameter of the first hole is 250-400 nm, and the ratio of the average pore diameter of the first hole to the average pore diameter of the second hole is 1.1-1.6; the pore area ratio of the pore wall of the first finger-shaped hole is 15%-35%, and the ratio of the pore area ratio of the pore wall of the first finger-shaped hole to the pore area ratio of the pore wall of the second finger-shaped hole is 0.5-0.9.

[0023] In this application, the average pore size of the first pore is 250-400 nm, allowing water vapor in the first flow channel to enter the first finger-shaped pores through the first pore, thereby increasing the water vapor permeation rate. If the average pore size of the first pore is too large, the mechanical strength of the first finger-shaped pore layer will decrease; if the average pore size of the first pore is too small, the water vapor permeation rate of the hollow fiber membrane will decrease. The ratio of the average pore size of the first pore to the average pore size of the second pore is 1.1-1.6, ensuring that water vapor passes through the hollow fiber membrane at a uniform speed, eliminating the phenomenon of reduced water vapor permeation rate due to uneven flow rate. If the ratio of the average pore size of the first pore to the average pore size of the second pore is too large, the amount of water vapor entering the first finger-shaped pore increases, thereby increasing the water vapor permeation rate and the amount of water vapor passing through. This can easily lead to blockage of the pores in the support layer or the pores in the condensation layer, preventing water vapor from diffusing to the outside of the membrane in time and reducing the water conversion efficiency; it also reduces the mechanical strength of the first finger-shaped pore layer. If the average pore size of the first pore is smaller than that of the second pore, the amount of water vapor passing through is reduced, which in turn reduces the water conversion efficiency of the hollow fiber membrane.

[0024] The first finger-shaped pores in this application have a suitable pore area ratio, ensuring appropriate water vapor throughput and permeation rate while maintaining the mechanical strength of the first finger-shaped pore layer, thus protecting the second finger-shaped pore layer. The ratio of the pore area ratio of the first finger-shaped pore wall to that of the second finger-shaped pore wall is 0.5-0.9, giving the hollow fiber membrane suitable mechanical strength and ensuring good deformation resistance of the first finger-shaped pore layer near the outer surface. Simultaneously, it allows water vapor to pass through all areas of the hollow fiber membrane at a uniform rate, preventing excessive water vapor velocity in any one area from reducing the water conversion efficiency of the hollow fiber membrane.

[0025] Furthermore, the support layer has support fibers forming a porous structure, the support fibers being strip-shaped, and the average diameter of the support fibers being 80-180 nm.

[0026] In this application, the average diameter of the supporting fibers in the support layer is 80-180 nm, giving the support layer a suitable average pore size, thereby allowing water vapor to have a suitable permeation rate. Simultaneously, the support layer possesses high mechanical strength to ensure the hollow fiber membrane's resistance to deformation and tensile strength. If the average diameter of the supporting fibers is too large, the average pore size of the support layer decreases, thus reducing the porosity of the support layer. This makes it easier for water vapor to clog the pores of the support layer, thereby reducing the water vapor permeation efficiency. If the average diameter of the supporting fibers is too small, the mechanical strength of the support layer decreases, thereby reducing the mechanical strength of the hollow fiber membrane. At the same time, it increases the rate at which water vapor passes through the support layer, causing a large amount of water vapor to enter the second finger-shaped pore layer. This results in a large amount of water vapor entering the condensation layer, easily causing concentration polarization at the condensation layer, thus reducing the water vapor permeation rate and consequently reducing the water conversion efficiency.

[0027] Furthermore, the thickness of the support layer is 5%-20% of the thickness of the hollow fiber membrane, the thickness of the support layer is 10%-30% of the average major diameter of the second finger-shaped pores, and the average pore size of the support layer is 200-300 nm.

[0028] In this application, the thickness of the support layer is 5%-20% of the thickness of the hollow fiber membrane. This ensures that the hollow fiber membrane has high mechanical properties and that water vapor accumulates in an appropriate amount within the support layer, resulting in a suitable amount of water vapor entering the second finger-shaped pore layer. This, in turn, ensures that water vapor flows through the hollow fiber membrane at a uniform speed. If the support layer is too thick, a large amount of water vapor accumulates within it, leading to a larger influx into the second finger-shaped pore layer. This increases the mass transfer resistance within the second finger-shaped pores, thereby reducing the water vapor permeation rate and consequently lowering the water conversion efficiency. Conversely, if the support layer is too thin, the mechanical strength of the hollow fiber is reduced, and the amount of water vapor accumulated within the support layer is smaller, resulting in a smaller concentration difference between the support layer and the second finger-shaped pore layer. This reduces the driving force for water vapor to move from the support layer to the second finger-shaped pore layer, further decreasing the water conversion efficiency.

[0029] In this application, the thickness of the support layer is 10%-30% of the average major diameter of the second finger-shaped pores, ensuring that the amount of water vapor accumulating within the support layer is relatively uniform, and that the water vapor entering the second finger-shaped pores has a relatively uniform flow rate within the support layer. The average pore size of the support layer in this application is 200-300 nm, ensuring both the mechanical strength of the support layer and the amount of water vapor accumulating within it, thus driving the water vapor to flow towards the second finger-shaped pore layer.

[0030] Furthermore, one side of the first finger-shaped pore layer is a first porous layer, and one side of the first porous layer is an outer surface. The thickness of the first porous layer accounts for 1%-10% of the thickness of the hollow fiber membrane, and the average pore size of the first porous layer is 50-150 nm. The first porous layer has a first fiber forming a porous structure. The first fiber is a strip structure, and the average diameter of the first fiber is 10-80 nm.

[0031] In this application, the thickness of the first porous layer accounts for 1%-10% of the thickness of the hollow fiber membrane, increasing the mechanical strength of the outer surface area to protect the first finger-shaped pore layer and enhance its resistance to deformation, thus protecting it and preventing structural collapse under external pressure. When the thickness of the first porous layer constitutes a large proportion of the hollow fiber membrane, the porosity of the hollow fiber membrane is reduced, and the amount of water vapor entering the membrane is also decreased. Conversely, when the thickness of the first porous layer constitutes a small proportion, its mechanical strength is reduced, causing it to lose its protective function for the first finger-shaped pore layer. This makes the first finger-shaped pore layer more susceptible to structural collapse under pressure, thereby reducing the water conversion efficiency of the hollow fiber membrane.

[0032] In this application, the first porous layer has a suitable average pore size, and the average diameter of the first fiber of the first porous layer is 10-80 nm. The first fiber has a suitable average diameter, which makes the first porous layer have a suitable average pore size, so that the water vapor entering the first porous layer has a suitable permeation rate, and the overall permeation rate of the hollow fiber membrane is more uniform; at the same time, it makes the first porous layer have better mechanical properties, which effectively protects the first finger-shaped pore layer.

[0033] Furthermore, the first porous layer also has a first skin region, one side of which is an outer surface, which is a dense surface, and the thickness of the first skin region accounts for 5%-25% of the thickness of the first porous layer.

[0034] In this application, the outer surface is a dense surface. A dense surface is defined as one where, when imaged under a scanning electron microscope at 50,000x magnification, the pore area ratio (i.e., pore area: inner surface area) of the inner surface is no greater than 6%, meaning either there are unobservable pore structures or a very small number of observable pore structures. Water vapor adsorbs on the outer surface, creating a concentration difference between the inside and outside of the hollow fiber membrane. This causes water vapor to migrate in clusters from the outer surface to the inside of the membrane, increasing water vapor permeation while significantly reducing gas permeation. The thickness of the first skin layer accounts for 5%-25% of the thickness of the first porous layer, giving the first porous layer greater mechanical strength and better protection for the first finger-shaped pore layer. If the thickness of the first skin layer is a large proportion of the total thickness of the porous layer, the rate at which water vapor enters the first porous layer decreases, thus reducing water vapor permeation. Conversely, if the thickness of the first skin layer is a small proportion of the total thickness of the porous layer, the mechanical strength of the first porous layer decreases, consequently reducing the mechanical strength of the hollow fiber membrane and its resistance to deformation. The outer surface of this application is dense, and the first skin layer has a suitable thickness, so that the first porous layer has a suitable water vapor permeation rate and mechanical strength.

[0035] Furthermore, the thickness of the condensation layer accounts for 3%-8% of the thickness of the hollow fiber membrane, the average pore size of the first porous layer is 1.1-1.5 times the average pore size of the condensation layer, and the ratio of the thickness of the condensation layer to the thickness of the second finger-shaped porous layer is 0.08-0.18; the condensation layer has a second fiber forming a porous structure, the second fiber is a strip structure, and the average diameter of the second fiber is 20-80 nm.

[0036] The thickness of the condensation layer in this application accounts for 3%-8% of the thickness of the hollow fiber membrane, ensuring a suitable permeation rate for water vapor within the membrane. This prevents excessively rapid water vapor permeation from clogging the pores of the condensation layer, thereby avoiding concentration polarization. The average pore size of the first porous layer is 1.1-1.5 times that of the condensation layer, allowing water vapor to enter the first finger-shaped pore layer at a faster rate, increasing the amount of water vapor entering the hollow fiber membrane and thus increasing the water conversion efficiency of the hollow fiber membrane. Water vapor then enters the second finger-shaped pore layer. The ratio of the thickness of the condensation layer to the thickness of the second finger-shaped pore layer is 0.08-0.18. Water vapor has a longer flow time in the second finger-shaped pore layer, and its permeation rate gradually decreases as it flows within this layer, allowing it to enter the condensation layer at a suitable speed. The suitable average pore size within the condensation layer causes the water vapor to liquefy into water, which then diffuses outwards along the condensation layer. The average pore size of the first porous layer and the condensation layer, the thickness of the condensation layer, and the thickness of the second finger-shaped pore layer all influence each other. Under the combined effect of these conditions, water vapor achieves a suitable permeation rate within the hollow fiber membrane. The second fiber of the condensation layer has a suitable average diameter, giving the condensation layer a suitable pore size, allowing water vapor to liquefy into water and diffuse towards the inner surface at a suitable rate; simultaneously, it gives the condensation layer high mechanical strength, thus contributing to the high mechanical strength of the hollow fiber membrane.

[0037] Furthermore, the condensation layer also has a second skin region, one side of which is an inner surface, which is a dense surface, and the thickness of the second skin region accounts for 1%-8% of the thickness of the condensation layer.

[0038] The inner surface of this application is a dense surface, defined as a surface where, when imaged under a scanning electron microscope at 50,000x magnification, the pore area ratio (i.e., pore area: inner surface area) of the inner surface is no greater than 6%, meaning either there are unobservable pore structures or a very small number of observable pore structures. When water from the condensate layer diffuses to the inner surface, it is carried away by the dry air within the hollow fiber membrane cavity. The thickness of the second skin layer accounts for 1%-8% of the thickness of the condensate layer, providing the condensate layer with suitable mechanical strength and, simultaneously, suitable water vapor permeation and water diffusion rates, thereby increasing the water conversion efficiency of the hollow fiber membrane.

[0039] Furthermore, the hollow fiber membrane has a porosity of 70%-88%, a thickness of 150-250 μm, a water conversion efficiency of 50%-70%, and an air permeability of 1-3 L / min / m³. 2 @80KPa, the water vapor permeation rate is 0.5-2.5g / min.

[0040] Flux refers to the amount of material passing through a unit area of ​​the hollow fiber membrane per unit time under a certain operating pressure during the separation process. In this application, the air flux is 10-25 ml / min / m². 2 @80KPa, its flux is relatively small, indicating that the air permeation flux of the hollow fiber membrane is relatively small; the water conversion efficiency of the hollow fiber membrane provided in this application is 50%-70%, ensuring a high water conversion efficiency, while having a small air permeation, so that the hollow fiber membrane has a good humidification effect.

[0041] The method for preparing the permeable finger-shaped hollow fiber membrane according to any one of the above-mentioned methods comprises the following steps in sequence:

[0042] S1: Preparation of casting solution and core solution;

[0043] The casting solution comprises the following components by weight: 16-21 parts of film-forming polymer, 1-5 parts of hydrophilic additive, and 74-83 parts of a first organic solvent; the temperature of the casting solution is 10-30°C; the film-forming polymer is any one of sulfone polymers, polyarylene ether nitrile, polyarylene ether nitrile, and polyacrylonitrile; the core solution comprises a non-solvent and a second organic solvent, the non-solvent being water, the non-solvent content being 70%-100%, and the temperature of the core solution being 10-30°C.

[0044] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0045] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 1-15 seconds, the relative humidity of the air bath is 80%-100%, and the temperature of the air bath is 5-10℃ lower than the temperature of the casting solution.

[0046] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 40-70℃, and the phase separation time is 15-55s. The coagulation bath is a mixture of water and a third organic solvent, and the water content in the coagulation bath is 70%-100%.

[0047] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0048] Furthermore, the casting solution further includes 1-6 parts of sulfonated polyethersulfone. The hydrophilic additive is at least one of polyvinylpyrrolidone, polyethylene glycol, diethylene glycol, and triethylene glycol; 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 dimethyl carbonate; the sulfone polymer is at least one of polyethersulfone, polysulfone, and polyarylsulfone.

[0049] In the above method, a casting solution and a core solution are prepared. The casting solution includes a film-forming polymer, a hydrophilic additive, and a first organic solvent. The hydrophilic additive is at least one of polyvinylpyrrolidone, polyethylene glycol, diethylene glycol, and triethylene glycol to increase the hydrophilicity of the casting solution. During the phase separation process, the organic solvent is more easily dissolved in the coagulation bath through its interaction with the coagulation bath, thereby making it easier for the film-forming polymer to precipitate and form a membrane with a suitable pore size. At the same time, the hydrophilicity of the prepared hollow fiber membrane is increased. When the film-forming polymer in the casting solution is a sulfone polymer, the hydrophilicity of the membrane can be further increased by adding a small amount of sulfonated polyether sulfone. If the content of sulfonated polyether sulfone is too high, the mechanical strength during the film formation process will be lower and the membrane will become brittle, thereby reducing the tensile strength of the hollow fiber membrane. The core liquid includes a second organic solvent and a high content of non-solvent (water). The water content in the core liquid is 70%-100%. When the casting liquid and the core liquid are extruded from the spinning nozzle at the same time, the temperature of the spinning nozzle and the temperature of the casting liquid are the same to avoid the temperature of the casting liquid being affected by the excessively high temperature of the spinning nozzle. As the non-solvent content in the core liquid increases, the porosity of the inner surface of the hollow fiber membrane decreases and the inner surface becomes smoother. As the water content in the core liquid increases, the chemical potential energy between the casting liquid and the core liquid gradually increases, which increases the exchange rate between the solvent in the casting liquid and the core liquid, making the inner surface of the membrane a dense surface. At the same time, a condensation layer is formed. The core liquid enters the interior of the membrane through the condensation layer, which greatly reduces the exchange rate between the solvent in the casting liquid and the core liquid, causing a second finger-like pore layer to form near the inner surface. Furthermore, since sulfonated polyethersulfone is water-soluble, according to the principle of "like dissolves like," it gradually migrates towards the core liquid. This results in a higher content of sulfonic acid groups on the inner surface compared to the outer surface, with the sulfonic acid group content gradually decreasing from the inner to the outer surface, leading to a gradual decrease in hydrophilicity from the inner to the outer surface. Placing the molded product with inner and outer surfaces in a high-humidity airflow accelerates phase separation, creating a dense outer surface. Simultaneously, a first porous layer with a sponge-like pore structure forms near the outer surface. The pre-separated molded product is then placed in a coagulation bath for further phase separation. The coagulation bath penetrates from the inner and outer surfaces along the membrane thickness direction towards the inner surface, causing phase separation and ensuring the full release of the first organic solvent. A suitable temperature in the coagulation bath results in double rows of finger-like pores in the hollow fiber membrane structure. However, if the coagulation bath temperature is too high, the double rows of finger-like pores in the membrane structure transform into a single row. The optimal temperature of the coagulation bath loosens the chain movement between macromolecular chains and polymer aggregates, resulting in double rows of finger-like pores with numerous finger-like structures. However, as the temperature increases further, secondary relaxation of the polymer reduces the pore size of the membrane network, leading to the formation of thicker sponge-like pores and a single layer of finger-like pores. Higher coagulation bath temperatures accelerate the formation of the membrane skin, which to some extent slows down the phase separation rate of the casting solution within the skin layer, resulting in the gradual replacement of the outer row of finger-like pores by sponge-like pores.When the water content in the coagulation bath is low, the coagulation bath penetrates from the outer surface into the hollow fiber membrane, resulting in a slow phase separation rate and the formation of a macroporous structure. It then gradually diffuses towards the inner surface, with the pore size decreasing gradually as the diffusion rate decreases, exhibiting a gradient distribution. When the water content in the coagulation bath is relatively high, the phase separation rate is faster, initially forming small-diameter pores. As the amount of coagulation bath penetrating increases, large-pore finger-like pores form. Once the coagulation bath penetrates to a certain thickness, the penetration rate gradually decreases, forming a support layer with a small-diameter structure. Furthermore, because the temperature of the air bath is lower than that of the casting solution, the air bath cools the membrane fibers, causing the skin layer near the outer surface to form faster. This slows down the phase separation rate of the casting solution within the skin layer to some extent. Therefore, the major axis of the second finger-like pore near the inner surface is larger than that of the first finger-like pore near the outer surface. The formed biofilm is stretched 1-5 times at a stretching rate of 3-12 m / min. This effectively prevents the shrinkage of pores caused by phase separation, thus achieving a shaping effect. Furthermore, at a suitable stretching rate, the pore size within the same layer is more uniform. An appropriate stretching ratio effectively avoids fiber breakage due to excessive stretching or poor stretching results due to insufficient stretching. Finally, the membrane is washed in water and then dried to obtain the hollow fiber membrane.

[0050] This application provides the following beneficial effects: the hollow fiber membrane exhibits a high water vapor permeation rate and water conversion efficiency, while ensuring the mechanical strength of the hollow fiber membrane and extending its service life. The preparation method provided by this invention can conveniently, quickly, and effectively prepare the aforementioned hollow fiber membrane. Attached Figure Description

[0051] The accompanying drawings, which are provided to further illustrate this application and form part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0052] Figure 1 The image shows a scanning electron microscope (SEM) image of the cross-section of the permeable finger-shaped hollow fiber membrane prepared in Example 1, with a magnification of 200×.

[0053] Figure 2 The image shows a scanning electron microscope (SEM) image of the longitudinal section of the second finger-shaped pore layer of the moisture-permeable finger-shaped hollow fiber membrane prepared in Example 1, with a magnification of 2000×.

[0054] Figure 3 The image shows a scanning electron microscope (SEM) image of the longitudinal section of the first finger-shaped pore layer of the moisture-permeable finger-shaped hollow fiber membrane prepared in Example 1, with a magnification of 2000×.

[0055] Figure 4The image shows a scanning electron microscope (SEM) image of the inner surface of the permeable finger-shaped hollow fiber membrane prepared in Example 1, with a magnification of 5000×.

[0056] Figure 5 The image shows a scanning electron microscope (SEM) image of the outer surface of the permeable finger-shaped hollow fiber membrane prepared in Example 1, with a magnification of 5000×.

[0057] Figure 6 The image shows a scanning electron microscope (SEM) image of the longitudinal section of the second finger-shaped pore layer of the moisture-permeable finger-shaped hollow fiber membrane prepared in Example 3, with a magnification of 5000×.

[0058] Figure 7 The image shows a scanning electron microscope (SEM) image of the longitudinal section of the condensation layer of the permeable finger-shaped hollow fiber membrane prepared in Example 3, with a magnification of 20000×.

[0059] Figure 8 The image shows a scanning electron microscope (SEM) image of the inner surface of the permeable finger-shaped hollow fiber membrane prepared in Example 3, with a magnification of 10000×.

[0060] Figure 9 The image shown is a scanning electron microscope (SEM) image of the surface of the permeable finger-shaped hollow fiber membrane prepared in Example 3, with a magnification of 10000×.

[0061] Figure 10 The image shows a scanning electron microscope (SEM) image of the longitudinal section of the first finger-shaped pore layer of the moisture-permeable finger-shaped hollow fiber membrane prepared in Example 3, with a magnification of 5000×.

[0062] Figure 11 The image shown is a scanning electron microscope (SEM) image of the first porous layer of the permeable finger-shaped hollow fiber membrane prepared in Example 3, with a magnification of 20000×.

[0063] Figure 12 The image shown is a scanning electron microscope (SEM) image of the cross-section of the permeable finger-shaped hollow fiber membrane support layer prepared in Example 3, with a magnification of 10000×. Detailed Implementation

[0064] To more clearly illustrate the overall concept of this application, detailed descriptions are provided below using examples. Unless otherwise specified, the raw materials and equipment used in the preparation of the hollow fiber membranes in the following examples are commercially available. Specifically, a Hitachi S-5500 scanning electron microscope was used to characterize the structural morphology of the filter membrane.

[0065] Example 1

[0066] S1: Preparation of casting solution and core solution;

[0067] The casting solution comprises the following components by weight: 18 parts polyethersulfone, 3.5 parts polyvinylpyrrolidone, 74 parts dimethylformamide, and 1 part sulfonated polyethersulfone. The temperature of the casting solution is 20°C. The core solution comprises water and dimethyl sulfoxide, with a water content of 85%. The temperature of the core solution is 27°C.

[0068] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0069] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 8 seconds, the relative humidity of the air bath is 85%, and the temperature of the air bath is 6.5℃ lower than the temperature of the casting solution.

[0070] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 45°C, and the phase separation time is 35s. The coagulation bath is a mixture of water and N-ethylpyrrolidone, and the water content in the coagulation bath is 80%.

[0071] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0072] Example 2

[0073] S1: Preparation of casting solution and core solution;

[0074] The casting solution comprises the following components by weight: 17 parts polysulfone, 2 parts diethylene glycol, and 76 parts dimethylacetamide, and the temperature of the casting solution is 15°C; the core solution comprises water and dimethylformamide, the water content is 90%, and the temperature of the core solution is 28°C.

[0075] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0076] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 12 seconds, the relative humidity of the air bath is 90%, and the temperature of the air bath is 7°C lower than the temperature of the casting solution.

[0077] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 50°C, and the phase separation time is 40s. The coagulation bath is a mixture of water and dimethyl sulfoxide, and the water content in the coagulation bath is 90%.

[0078] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0079] Example 3

[0080] S1: Preparation of casting solution and core solution;

[0081] The casting solution comprises the following components by weight: 17.5 parts polyarylsulfone, 2.5 parts triethylene glycol, 77 parts dimethyl sulfoxide, and 3 parts sulfonated polyethersulfone. The temperature of the casting solution is 18°C. The core solution comprises water and N-methylpyrrolidone, with a water content of 95%. The temperature of the core solution is 25°C.

[0082] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0083] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 10 seconds, the relative humidity of the air bath is 83%, and the temperature of the air bath is 8°C lower than the temperature of the casting solution.

[0084] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 55°C, and the phase separation time is 55s. The coagulation bath is a mixture of water and N-ethylpyrrolidone, and the water content in the coagulation bath is 95%.

[0085] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0086] Example 4

[0087] S1: Preparation of casting solution and core solution;

[0088] The casting solution comprises the following components by weight: 16 parts polyethersulfone, 3 parts polyethylene glycol, and 79 parts dimethylacetamide, and the temperature of the casting solution is 12°C; the core solution comprises water and N-methylpyrrolidone, the water content is 80%, and the temperature of the core solution is 20°C.

[0089] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0090] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 13 seconds, the relative humidity of the air bath is 95%, and the temperature of the air bath is 7.5°C lower than the temperature of the casting solution.

[0091] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a green film. The temperature of the coagulation bath is 60°C, and the phase separation time is 45s. The coagulation bath is a mixture of water and dimethylformamide, and the water content in the coagulation bath is 85%.

[0092] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0093] Example 5

[0094] S1: Preparation of casting solution and core solution;

[0095] The casting solution comprises the following components by weight: 18 parts polyarylsulfone, 1 part diethylene glycol, and 80 parts N-ethylpyrrolidone, and the temperature of the casting solution is 25°C; the core solution comprises water and dimethylacetamide, the water content is 75%, and the temperature of the core solution is 18°C.

[0096] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0097] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 6 seconds, the relative humidity of the air bath is 87%, and the temperature of the air bath is 8.5℃ lower than the temperature of the casting solution.

[0098] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 65°C, and the phase separation time is 25s. The coagulation bath is a mixture of water and dimethyl sulfoxide, and the water content in the coagulation bath is 75%.

[0099] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0100] Example 6

[0101] S1: Preparation of casting solution and core solution;

[0102] The casting solution comprises the following components by weight: 19.5 parts polysulfone, 4 parts triethylene glycol, 81 parts dimethylformamide, and 4 parts sulfonated polyethersulfone. The temperature of the casting solution is 23°C. The core solution comprises water and N-ethylpyrrolidone, with a water content of 78%. The temperature of the core solution is 15°C.

[0103] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0104] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 7 seconds, the relative humidity of the air bath is 94%, and the temperature of the air bath is 9°C lower than the temperature of the casting solution.

[0105] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 40°C, and the phase separation time is 30s. The coagulation bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulation bath is 70%.

[0106] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0107] Example 7

[0108] S1: Preparation of casting solution and core solution;

[0109] The casting solution comprises the following components by weight: 20 parts polyarylsulfone, 4.5 parts diethylene glycol, 82 parts N-ethylpyrrolidone, and 5 parts sulfonated polyethersulfone. The temperature of the casting solution is 27°C. The core solution comprises water and N-methylpyrrolidone, with a water content of 83%. The temperature of the core solution is 12°C.

[0110] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0111] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 5 seconds, the relative humidity of the air bath is 98%, and the temperature of the air bath is 9.5℃ lower than the temperature of the casting solution.

[0112] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a green film. The temperature of the coagulation bath is 70°C, and the phase separation time is 50s. The coagulation bath is a mixture of water and dimethylformamide, and the water content in the coagulation bath is 93%.

[0113] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0114] Example 8

[0115] S1: Preparation of casting solution and core solution;

[0116] The casting solution comprises the following components by weight: 21 parts polysulfone, 5 parts polyvinylpyrrolidone, 83 parts dimethylacetamide, and 6 parts sulfonated polyethersulfone. The temperature of the casting solution is 25°C. The core solution comprises water and dimethyl sulfoxide, with a water content of 92%. The temperature of the core solution is 23°C.

[0117] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0118] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 9 seconds, the relative humidity of the air bath is 92%, and the temperature of the air bath is 6°C lower than the temperature of the casting solution.

[0119] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 58°C, and the phase separation time is 48s. The coagulation bath is a mixture of water and dimethylformamide, and the water content in the coagulation bath is 87%.

[0120] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0121] Example 9

[0122] S1: Preparation of casting solution and core solution;

[0123] The casting solution comprises the following components by weight: 19 parts polyarylene ether nitrile, 4.5 parts polyvinylpyrrolidone, and 80 parts N-methylpyrrolidone, and the temperature of the casting solution is 27°C; the core solution comprises water and dimethyl carbonate, with a water content of 90%, and the temperature of the core solution is 20°C.

[0124] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0125] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 12 seconds, the relative humidity of the air bath is 94%, and the temperature of the air bath is 5°C lower than the temperature of the casting solution.

[0126] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a green film. The temperature of the coagulation bath is 62°C, and the phase separation time is 47s. The coagulation bath is a mixture of water and dimethylacetamide, and the water content in the coagulation bath is 85%.

[0127] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0128] Example 10

[0129] S1: Preparation of casting solution and core solution;

[0130] The casting solution comprises the following components by weight: 20 parts polyarylene ether nitrile, 5 parts polyvinylpyrrolidone, and 82 parts dimethylacetamide, and the temperature of the casting solution is 22°C; the core solution comprises water and N-methylpyrrolidone, with a water content of 79%, and the temperature of the core solution is 24°C.

[0131] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0132] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 8 seconds, the relative humidity of the air bath is 91%, and the temperature of the air bath is 7°C lower than the temperature of the casting solution.

[0133] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 57°C, and the phase separation time is 49s. The coagulation bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulation bath is 88%.

[0134] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0135] Example 11

[0136] S1: Preparation of casting solution and core solution;

[0137] The casting solution comprises the following components by weight: 17 parts polyacrylonitrile, 2 parts triethylene glycol, and 76 parts dimethyl sulfoxide, and the temperature of the casting solution is 17.5°C; the core solution comprises water and dimethylacetamide, the water content is 93%, and the temperature of the core solution is 24°C.

[0138] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0139] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 9 seconds, the relative humidity of the air bath is 82%, and the temperature of the air bath is 7.5°C lower than the temperature of the casting solution.

[0140] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 53°C, and the phase separation time is 54s. The coagulation bath is a mixture of water and dimethylformamide, and the water content in the coagulation bath is 94%.

[0141] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0142] Comparative Example 1

[0143] S1: Preparation of casting solution and core solution;

[0144] The casting solution comprises the following components by weight: 18 parts polyethersulfone, 3.5 parts polyvinylpyrrolidone, 74 parts dimethylformamide, and 1 part sulfonated polyethersulfone. The temperature of the casting solution is 20°C. The core solution comprises water and dimethyl sulfoxide, with a water content of 55%. The temperature of the core solution is 27°C.

[0145] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0146] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 8 seconds, the relative humidity of the air bath is 89%, and the temperature of the air bath is 5°C higher than the temperature of the casting solution.

[0147] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 45°C, and the phase separation time is 35s. The coagulation bath is a mixture of water and N-ethylpyrrolidone, and the water content in the coagulation bath is 70%.

[0148] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0149] Compared with Example 1, Comparative Example 1 increased the temperature of the air bath, making the average length diameter of the first finger-shaped hole much larger than that of the second finger-shaped hole, which greatly reduced the mechanical strength of the hollow fiber membrane.

[0150] Comparative Example 2

[0151] S1: Preparation of casting solution and core solution;

[0152] The casting solution comprises the following components by weight: 18 parts polyethersulfone, 3.5 parts polyvinylpyrrolidone, 74 parts dimethylformamide, and 1 part sulfonated polyethersulfone. The temperature of the casting solution is 20°C. The core solution comprises water and dimethyl sulfoxide, with a water content of 85%. The temperature of the core solution is 27°C.

[0153] S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface;

[0154] S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 8 seconds, the relative humidity of the air bath is 80%, and the temperature of the air bath is 6.5℃ lower than the temperature of the casting solution.

[0155] S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a film. The temperature of the coagulation bath is 80°C, and the phase separation time is 35s. The coagulation bath is a mixture of water and N-ethylpyrrolidone, and the water content in the coagulation bath is 80%.

[0156] S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

[0157] Under the same conditions as in Comparative Example 2 and Example 1, the temperature of the coagulation bath was increased, resulting in a single-layer finger-shaped pore structure with only the first finger-shaped pore. This significantly reduced the mechanical strength of the hollow fiber membrane and also reduced its water conversion efficiency.

[0158] Performance Experiment

[0159] Structural characterization

[0160] The hollow fiber membranes obtained in each embodiment and comparative example were characterized by longitudinal section, inner surface, and outer surface morphology. The thickness, average pore size, and fiber density of each layer in the main body were measured, as well as the average fiber diameter, porosity, and thickness of the hollow fiber membrane. The measurement data are shown in Tables 1-4. The morphology characterization results of Examples 1-11 are shown in... Figures 1-12 .

[0161] Table 1 Characterization of each example membrane structure

[0162]

[0163]

[0164] Table 2 Characterization of each example membrane structure

[0165]

[0166] Table 3 Characterization of each example membrane structure

[0167]

[0168]

[0169] Table 4 Characterization of each example membrane structure

[0170]

[0171] Performance testing

[0172] The tensile strength and elongation of the hollow fiber membranes obtained in each example were tested using a tensile testing machine.

[0173] The water conversion efficiency of the hollow fiber membranes obtained in each example was tested.

[0174] A homemade hollow fiber component was used, with humid air entering through the wet in end and dry air through the dry in end. Digital display thermometers and hygrometers were used to monitor the humidification effect at both the dry out and wet out ends. Different humidification data were obtained by varying the gas flow rates at the dry in and wet in ends. Different humidification data were also obtained by adding a one-way pressure relief valve at the dry out end to increase the pressure of the dry flow.

[0175] Calculation results: Where: D—density of dry gas or wet vapor, unit (g / m³) 3 K1, K2—constants; T—temperature at the dry-in end, dry-out end, wet-in end, or wet-out end of the hollow fiber membrane, in °C; T1—temperature constant, in °C. —Humidity of the dry in end, dry out end, wet in end, or wetout end of the hollow fiber membrane, in %RH.

[0176] V = Q * H Where: V—volume of dry or moist gas, unit (m³) 3 Q—volume flow rate of dry or wet gas, in units of (m³ / s). 3 / h), H—gas flow rate time, in hours.

[0177] m = ρ * v where m—water content at the dry out end or wet in end of the hollow fiber membrane, in g; ρ—density of dry gas or wet vapor, in g / m³. 3 v—volume of dry or moist gas, unit (m³) 3 ). In the formula, ω is the water conversion efficiency, m1 is the water content at the dry out end of the hollow fiber membrane (in g), and m2 is the water content at the wet in end of the hollow fiber membrane (in g).

[0178] The air permeability of the hollow fiber membranes obtained in each example was tested using a gas flow meter.

[0179] Table 5 Hollow Fiber Membrane Performance Tests

[0180]

[0181] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A permeable finger-shaped hollow fiber membrane, comprising a main body, one side of which is an inner surface and the other side is an outer surface, wherein the main body has non-directional tortuous pathways, characterized in that, The main body includes a first finger-shaped pore layer and a second finger-shaped pore layer. The first finger-shaped pore layer is located near the outer surface region of the main body, and the second finger-shaped pore layer is located near the inner surface region of the main body. The side of the second finger-shaped pore layer near the inner surface is a condensation layer for water vapor condensation, and the side of the condensation layer is the inner surface. A support layer with a sponge-like porous structure is located between the first finger-shaped pore layer and the second finger-shaped pore layer; the first finger-shaped pore layer, the support layer, and the second finger-shaped pore layer are connected by a continuous fiber transition. The first finger-shaped pore layer has a plurality of first finger-shaped pores distributed along the circumference of the membrane, and the second finger-shaped pore layer has a plurality of second finger-shaped pores distributed along the circumference of the membrane; the major axis of the first and second finger-shaped pores extends radially into the hollow fiber membrane, and the minor axis of the first and second finger-shaped pores extends circumferentially into the hollow fiber membrane; the average major axis of the first finger-shaped pores is 40-65 μm; the average major axis of the second finger-shaped pores is 10-30 μm longer than the average major axis of the first finger-shaped pores. The ratio of the average major axis to the average minor axis of the first finger-shaped aperture is 5.5-7; The ratio of the average major axis to the average minor axis of the second finger-shaped aperture is 7.5-9.5; The support layer has support fibers forming a porous structure, and the average diameter of the support fibers is 80-180 nm. The average pore size of the support layer is 200-300 nm; One side of the first finger-shaped pore layer is a first porous layer, and one side of the first porous layer is an outer surface. The first porous layer has a first fiber forming a porous structure, and the average diameter of the first fiber is 10-80 nm.

2. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The average major diameter of the second finger-shaped aperture is 60-85 μm.

3. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The average short diameter of the second finger-shaped aperture is 6.5-9.5 μm, and the ratio of the average short diameter of the second finger-shaped aperture to the average short diameter of the first finger-shaped aperture is 0.7-1.

2.

4. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The sum of the average major diameter of the first finger-shaped hole and the average major diameter of the second finger-shaped hole accounts for 60%-80% of the thickness of the hollow fiber membrane.

5. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The distance between two adjacent first finger-shaped holes is the first distance, and the average length of the first distance is 2-6 μm; The distance between two adjacent second finger-shaped holes is the second distance, and the ratio of the average length of the second distance to the average length of the first distance is 0.1-0.

5.

6. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The wall of the first finger-shaped hole has a plurality of first holes, and the diameter of the first hole near the support layer is larger than the diameter of the first hole near the outer surface; The second finger-shaped hole has a plurality of second holes in its wall, and the diameter of the second hole near the support layer is larger than the diameter of the second hole near the inner surface.

7. The permeable finger-shaped hollow fiber membrane according to claim 6, characterized in that, The average pore size of the first hole is 250-400 nm, and the ratio of the average pore size of the first hole to the average pore size of the second hole is 1.1-1.

6. The pore area ratio of the first finger-shaped hole wall is 15%-35%, and the ratio of the pore area ratio of the first finger-shaped hole wall to the pore area ratio of the second finger-shaped hole wall is 0.5-0.

9.

8. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The supporting fibers have a strip-shaped structure.

9. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The thickness of the support layer is 5%-20% of the thickness of the hollow fiber membrane, and the thickness of the support layer is 10%-30% of the average major diameter of the second finger-shaped pores.

10. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The thickness of the first porous layer accounts for 1%-10% of the thickness of the hollow fiber membrane, and the average pore size of the first porous layer is 50-150 nm. The first fiber has a strip-like structure.

11. The permeable finger-shaped hollow fiber membrane according to claim 10, characterized in that, The first porous layer also has a first skin region, one side of which is an outer surface, which is a dense surface, and the thickness of the first skin region accounts for 5%-25% of the thickness of the first porous layer.

12. The permeable finger-shaped hollow fiber membrane according to claim 10, characterized in that, The thickness of the condensation layer accounts for 3%-8% of the thickness of the hollow fiber membrane, the average pore size of the first porous layer is 1.1-1.5 times the average pore size of the condensation layer, and the ratio of the thickness of the condensation layer to the thickness of the second finger-shaped porous layer is 0.08-0.

18. The condensation layer has a second fiber forming a porous structure. The second fiber has a strip-like structure and an average diameter of 20-80 nm.

13. The permeable finger-shaped hollow fiber membrane according to claim 12, characterized in that, The condensation layer also has a second skin region, one side of which is an inner surface, which is a dense surface, and the thickness of the second skin region accounts for 1%-8% of the thickness of the condensation layer.

14. The permeable finger-shaped hollow fiber membrane according to claim 1, characterized in that, The hollow fiber membrane has a porosity of 70%-88%, a thickness of 150-250 μm, a water conversion efficiency of 50%-70%, and an air permeability of 1-3 L / min / m. 2 @80KPa, the water vapor permeation rate is 0.5-2.5g / min.

15. The method for preparing a moisture-permeable finger-shaped hollow fiber membrane according to any one of claims 1 to 14, characterized in that, The steps are as follows: S1: Preparation of casting solution and core solution; The casting solution comprises the following components by weight: 16-21 parts of film-forming polymer, 1-5 parts of hydrophilic additive and 74-83 parts of first organic solvent, and the temperature of the casting solution is 10-30℃. The film-forming polymer is any one of sulfone polymers, polyarylene ether nitrile, polyarylene ether nitrile and polyacrylonitrile; The core fluid includes a non-solvent and a second organic solvent, wherein the non-solvent is water, the content of the non-solvent is 70%-100%, and the temperature of the core fluid is 10-30℃. S2: Spinning, the casting solution and the core solution are simultaneously extruded from the spinning nozzle to form a molded product with an inner surface and an outer surface; S3: Pre-phase separation, the molded product is subjected to pre-phase separation in an air bath for 1-15 seconds, the relative humidity of the air bath is 80%-100%, and the temperature of the air bath is 5-10℃ lower than the temperature of the casting solution. S4: The pre-phase separated molded product is placed in a coagulation bath for further phase separation to form a green film. The temperature of the coagulation bath is 40-70℃, and the phase separation time is 15-55s. The coagulation bath is a mixture of water and a third organic solvent, and the water content in the coagulation bath is 70%-100%. S5: The raw film is stretched, washed in water, and finally dried to obtain a hollow fiber membrane.

16. The preparation method according to claim 15, characterized in that, The casting solution also includes 1-6 parts of sulfonated polyether sulfone.

17. The preparation method according to claim 15, characterized in that, The hydrophilic additive is at least one of polyvinylpyrrolidone, polyethylene glycol, diethylene glycol, and triethylene glycol; 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 dimethyl carbonate; The sulfone polymer is at least one of polyethersulfone, polysulfone, and polyarylsulfone.

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