Highly moisture permeable and low air permeable hollow fiber membrane, and preparation method and use thereof

Abstract

The application relates to the technical field of moisture-permeable membrane materials, and provides a high-moisture-permeable low-air-permeable hollow fiber membrane and a preparation method and application thereof. The high-moisture-permeable low-air-permeable hollow fiber membrane comprises a main body, one side of the main body is an inner surface, the other side is an outer surface, the main body has a non-directional zigzag path inside, wherein the average pore size of the main body changes in a gradient from the region close to the outer surface side to the region close to the inner surface side. The main body comprises a capillary condensation layer and a supporting layer, one side of the capillary condensation layer is an inner surface, and one side of the supporting layer is an outer surface. The other side of the capillary condensation layer and the other side of the supporting layer are connected through continuous fibers. The average pore size of the outer surface is 200-650 nm. The inner surface is a dense surface. The polysulfone hollow fiber membrane structure provided by the application shows high water conversion efficiency, low gas throughput and good tensile strength, and can also be operated for a long time under high temperature and high pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of moisture permeable membrane materials, in particular to a high-moisture-permeable low-air-permeable hollow fiber membrane and a preparation method and application thereof. BACKGROUND

[0002] Polysulfone polymer is an excellent membrane material, and the hollow fiber membrane prepared therefrom has high pressure resistance, heat resistance and oxidation resistance, and good biocompatibility, and has certain hydrophilicity. Among them, polysulfone polymer microporous membrane is widely used in industrial, pharmaceutical or medical fields.

[0003] The hollow fiber membrane has a fiber shape and is a self-supporting asymmetric membrane, and the dense layer is located on the outer surface or the inner surface of the fiber. Hollow fiber membrane is an important form of separation membrane, including hollow fiber ultrafiltration membrane, hollow fiber microfiltration membrane, hollow fiber reverse osmosis membrane and hollow fiber gas separation membrane. It is mainly used in water purification, pharmaceutical purification and humidification treatment fields.

[0004] Hollow fiber gas separation membrane includes moisture permeable hollow fiber membrane, which is mainly used in humidifiers and generally has good hydrophilicity and selective permeability. Water vapor in air is separated from other gas components, and water vapor is transmitted from the side with high humidity to the side with low humidity.

[0005] The patent CN102481524B disclosed by Toray Industries, Inc. in 2014 provides a water vapor permeable membrane, and the hollow fiber membrane and the hollow fiber membrane assembly prepared therefrom are suitable for fuel cell systems. The membrane has an asymmetric shape, one side of the membrane has a dense layer, and the other side of the membrane has a finger-shaped hole. Such structure ensures the water vapor permeability, but the area of the hollow core of the finger-shaped hole is large, resulting in low tensile strength and unable to withstand large pressure.

[0006] At present, how to prepare a hollow fiber membrane with high tensile strength and excellent moisture permeability is a problem to be solved by those skilled in the art. SUMMARY

[0007] In order to solve the above problems, the present application aims to provide a high-moisture-permeable low-air-permeable hollow fiber membrane and a preparation method thereof, wherein the hollow fiber membrane can exhibit high water conversion efficiency, high tensile strength and low gas throughput, greatly improving the performance of the hollow fiber membrane made of polysulfone polymer as the main material and prolonging the service life thereof.

[0008] In one aspect, a high moisture permeable and low air permeable hollow fiber membrane includes a main body, one side of the main body is an inner surface, the other side is an outer surface, and the main body has a non-directional tortuous path inside, wherein the average pore size of the main body changes from the area close to the outer surface side to the area close to the inner surface side; the main body includes a capillary condensation layer and a support layer, one side of the capillary condensation layer is an inner surface, and one side of the support layer is an outer surface; the other side of the capillary condensation layer and the other side of the support layer are connected by continuous fibers; the average pore size of the outer surface is 200-650nm; and the inner surface is a dense surface.

[0009] In the present application, the dense surface is that the pore area ratio (i.e. the pore area: the inner surface area) of the inner surface is not more than 6% when the scanning electron microscope is taken at 50000 times, that is, there are two cases of unobservable pore structure or a small number of observable pore structures, and the pore diameter of the observable pore structure is not more than 50nm, further preferably not more than 20nm, and more preferably not more than 10nm. The capillary condensation layer is the area where water vapor is converted from vapor to liquid. The support layer is the area where water vapor penetrates into the hollow fiber membrane and diffuses in the form of vapor. The "continuous fiber transition" can be understood as the fibers between the capillary condensation layer and the support layer are "integrally formed" in the form of whole continuous connection, and the continuous fibers cannot be separated from each other unless torn by external force. The measurement method of the average pore size of the membrane surface can be measured by using a scanning electron microscope to characterize the morphology of the membrane structure, and then using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement, and corresponding calculation; in the preparation process of the membrane, in the direction perpendicular to the thickness direction of the membrane (if the membrane is a flat membrane form, the direction is the plane direction; if the membrane is a hollow fiber membrane form, the direction is perpendicular to the radius direction), the characteristics such as the pore size distribution are generally uniform and consistent; therefore, the average pore size of the partial area on the corresponding plane can reflect the average pore size of the whole on the plane. In actual measurement, the surface of the membrane can be characterized by an electron microscope to obtain the corresponding SEM image, and since the pore of the membrane surface is generally uniform, a certain area can be selected, for example, 1μm 2 (1μm by 1μm) or 25μm 2(5 μm by 5 μm), and the specific area size is determined according to the actual situation, and then the pore diameters of all the holes in the area are measured by using corresponding computer software or manually, and then calculation is performed to obtain the average pore diameter of the surface. Of course, the above-mentioned parameters can also be obtained by other measuring means by those skilled in the art, and the above-mentioned measuring means are only for reference. In the present application, the capillary condensation layer and the support layer are both composed of the same material, and the two layers are combined into an integral structure and are directly formed in the membrane preparation process, and there is only a change in the membrane structure in the transition from the capillary condensation layer to the support layer, so the membrane prepared in the present application is an asymmetric membrane; in contrast, for example, a composite membrane has a multi-layer structure, and it is coated with a dense layer as a separation layer on a porous, often microporous, support layer or support membrane by using a separate process step, and the materials constituting the support layer and the separation layer in the composite membrane are often different.

[0010] In the hollow fiber membrane provided in the present application, the non-directional and tortuous passages between the inner surface and the outer surface of the main body form a sponge-like network structure. The average pore diameter of the main body changes in a gradient from the region close to the outer surface side to the region close to the inner surface side, and further, the gradient gradually decreases. Wherein, "gradually decreases" can be understood as monotonic decrease, that is, for any two average pore diameters X1 and X2, when X2 < X1, f(X2) < f(X1), and the average pore diameter is continuously decreasing, that is, there is no fluctuation state of increasing, decreasing, or decreasing, then stable. In the present application, the average pore diameter of the membrane gradually decreases from the region close to the outer surface to the region close to the inner surface. Compared with the finger-like hole in the prior art, the inside of the membrane is formed by the complex fibers to form non-directional and tortuous holes, which avoids the local hollow part with too large area, which leads to low tensile strength of the membrane, and ensures that the hollow fiber membrane prepared in the present application has large tensile strength. In addition, it should be noted that the gradient change of the pore diameter of the membrane reflects the change of the overall pore diameter on the cross section of the main body, and does not include the few moisture-permeable holes that occasionally appear on the cross section. The pore diameter of these moisture-permeable holes is larger than that of the nearby holes.

[0011] The subject in the application can be divided into a support layer and a capillary condensation layer according to the size of the area aperture, and the average aperture of the capillary condensation layer is smaller than the average aperture of the support layer. Water vapor enters the hollow fiber membrane from the pores on the outer surface of the support layer. According to the capillary condensation theory, during the permeation process, the water vapor will condense into liquid water due to the gradual decrease of the membrane aperture, that is, into the capillary condensation layer. At this time, the water concentration near the inner surface region of the hollow fiber membrane is greater than the water concentration on the inner surface, forming a concentration difference, and the water diffuses from the high concentration to the low concentration, that is, the water diffuses from the region near the inner surface to the inner surface. The dry air in the lumen of the hollow fiber membrane will diffuse to the water on the inner surface, increasing the humidity of the air in the lumen, thereby playing a humidifying role. On the one hand, when the steam condenses into water in the capillary condensation layer, the water will block the flow channel near the inner surface region, which can effectively prevent other gases from passing through, thereby reducing the amount of gas passing through. On the other hand, the aperture of the pores on the dense surface formed by the application is extremely small, which further reduces the amount of gas passing through, and the low pore area ratio of the dense surface makes it have a large mechanical strength, so that the dense surface supports the whole hollow fiber membrane, making the membrane have good mechanical strength and not easy to be damaged under a large pressure, thereby increasing its service life.

[0012] wherein the average aperture of the outer surface is 200-650nm, when the average aperture of the outer surface is too large, the mechanical strength is reduced, when the membrane is subjected to too large pressure, the pores near the outer surface region are easy to collapse, causing the membrane to deform or break, thereby affecting the performance of the membrane; and when the average aperture of the outer surface is too large, the amount of gas passing through the outer surface into the hollow fiber membrane increases, thereby increasing the amount of gas passing through the hollow fiber membrane. When the average aperture of the outer surface is small, the amount of water vapor passing through is reduced, thereby affecting the water conversion efficiency. The outer surface of the hollow fiber membrane prepared by the application has a suitable average aperture, which not only ensures the amount of water vapor passing through, but also reduces the amount of gas passing through, and also meets the mechanical strength of the outer surface, thereby making the whole membrane have good tensile strength.

[0013] In summary, the hollow fiber membrane provided by the application has better tensile strength, lower gas passing amount and better water vapor passing amount, thereby improving the humidifying effect of the membrane.

[0014] Further, the average aperture variation gradient of the hollow fiber membrane is 2-8nm / μm, and the porosity of the hollow fiber membrane is 60%-85%.

[0015] It should be noted that the average aperture variation gradient of the hollow fiber membrane in the application is calculated according to the formula:

[0016]

[0017] wherein, — the average pore size gradient in the membrane thickness direction, in units of (nm / μm); — the average pore size of the outer surface, in units of (nm); — the average pore size of the inner surface, in units of (nm); T — the hollow fiber membrane thickness, in units of (μm).

[0018] The average pore size in the membrane thickness direction in the present application is in the range of 2-8 nm / μm, and preferably, the average pore size gradient is 3-7 nm / μm. The suitable average pore size gradient range makes the hollow part of the pore in the hollow fiber membrane more evenly distributed in the gradient change, so that the overall hollow fiber membrane has greater tensile strength. At the same time, as the average pore size of the hollow fiber membrane is in the suitable range, it has a larger porosity, which is in the range of 60-85%, which is conducive to the increase of water conversion efficiency, thereby increasing the humidification effect of the membrane.

[0019] Further, the first water contact angle of the inner surface is smaller than that of the outer surface by 8-35°, preferably, 12-32°, more preferably, 15-28°, and the first water contact angle in the membrane thickness direction from the inner surface to the outer surface is gradiently changed.

[0020] It should be noted that the hollow fiber membrane can be first torn into several layers, and then the contact angle tester is used to test the corresponding parameters, or the above-mentioned parameters can be obtained by other measuring means by those skilled in the art, and the above-mentioned measuring means are only for reference.

[0021] The first water contact angle in the membrane thickness direction from the inner surface to the outer surface in the present application is gradiently increased. Since the water contact angle of the membrane surface is related to the hydrophilicity of the membrane surface (i.e., the larger the first water contact angle, the worse the hydrophilicity; the smaller the first water contact angle, the better the hydrophilicity), the hydrophilicity in the membrane thickness direction from the inner surface to the outer surface is gradiently decreased. The change of hydrophilicity is also one of the driving forces for water movement, i.e., water moves from a place with weak hydrophilicity to a place with strong hydrophilicity, i.e., under the gradient change of hydrophilicity, the water in the hollow fiber membrane flows to the inner surface with better hydrophilicity. When the first contact angle of the inner and outer surfaces is large, the water contact angle of the inner surface is too small, and water is easily stored in the inner surface and is not easy to diffuse outward, thereby reducing the humidification effect of the hollow fiber membrane. When the first contact angle of the inner and outer surfaces is small, the driving force for water movement in the flow channel is reduced, which reduces the water conversion efficiency, and in turn reduces the humidification effect of the hollow fiber membrane. Through a large number of tests, it is found that the water contact angle of the inner surface is smaller than that of the outer surface by 8-35°, which is a suitable range, so that the water in the hollow fiber membrane flows to the inner surface and is easy to diffuse outward, thereby increasing the humidification effect of the hollow fiber membrane.

[0022] Further, the first water contact angle of the inner surface is 45-75°, and the first water contact angle of the outer surface is 60-89°.

[0023] It should be noted that when the water contact angle of the inner surface is small, the hydrophilicity of the inner surface is large, so that water is gathered in the area close to the inner surface of the membrane, thereby reducing the diffusion rate of water. When the first water contact angle of the inner surface is too large, the hydrophilicity of the area close to the inner surface is small, so that the flow rate of water in the flow channel close to the inner surface is reduced, thereby reducing the diffusion rate of water. The inner surface of the present application has a suitable first water contact angle, so that the water in the hollow fiber membrane flows to the inner surface at a suitable flow rate, and the water on the inner surface is not gathered, thereby increasing the humidification effect of the membrane. When the water contact angle of the outer surface is too large, the hydrophobicity of the area close to the outer surface is large, so that the amount of water vapor entering the outer surface area is reduced. When the water contact angle of the outer surface is small, the hydrophilicity of the area close to the outer surface is large, which is not conducive to the diffusion of water vapor to the inner surface, thereby reducing the amount of water vapor passing through. The outer surface of the present application has a suitable first water contact angle, which increases the amount of water vapor entering the outer surface, while effectively preventing water vapor from gathering in the outer surface area, which helps to improve the water conversion efficiency of the hollow fiber membrane.

[0024] Further, the roughness of the inner surface is smaller than the roughness of the outer surface.

[0025] It should be noted that when the surface roughness of the membrane is large, the solid surface free energy is low, so that it has a large first water contact angle, thereby having poor hydrophilicity. When the surface roughness of the membrane is low, the solid surface free energy is high, so that it has a small first water contact angle, thereby having good hydrophilicity. The outer surface has a relatively large roughness, and when the gas passes through the outer surface, it is easy to be adsorbed on the outer surface with large roughness, thereby reducing the amount of gas passing through. In the present application, the roughness of the inner surface is smaller than the roughness of the outer surface, that is, the hydrophilicity of the inner surface is better than that of the outer surface, which provides a driving force for the water inside the hollow fiber membrane to flow to the inner surface. When the inner surface is smooth, the energy loss is small when the gas blows through the inner surface, thereby having a small pressure drop. Pressure drop is the change of energy. The pressure decreases due to energy loss when the gas flows in the pipe. This energy loss is caused by the mutual collision and exchange of momentum between gas particles when the gas flows, which causes a pressure difference before and after the gas flow, that is, pressure drop. The roughness tester is used to test the roughness of the hollow fiber membrane in the present application, and it is found that the inner and outer surfaces have suitable roughness, so that the inner and outer surfaces have suitable hydrophilicity, which is helpful for the permeation of water vapor.

[0026] Further, the thickness of the capillary condensation layer is 8-25 μm, and the percentage of the thickness of the capillary condensation layer to the thickness of the hollow fiber membrane is 8%-20%.

[0027] It should be noted that the thickness of the capillary condensation layer in the present application accounts for the percentage of the thickness of the main body of the hollow fiber membrane, which determines the water conversion efficiency and the gas throughput. When the percentage is large, the capillary condensation layer is thick, which slows down the diffusion speed of the condensed water of water vapor in the hollow fiber membrane, thereby reducing the throughput of water vapor. When the percentage is too small, the capillary condensation layer is thin, although it speeds up the diffusion speed of the condensed water of water vapor in the hollow fiber membrane, with the increase of the flow speed of water in the flow channel, the effect of blocking gas is reduced, which increases the throughput of gas. Therefore, the appropriate thickness of the capillary condensation layer and the percentage of the capillary condensation layer in the thickness of the hollow fiber membrane help to improve the water conversion efficiency, while effectively avoiding the permeation of gas.

[0028] As a preferred embodiment, the thickness of the capillary condensation layer in the present application is 8-25 μm, preferably 12-20 μm. The percentage of the capillary condensation layer in the thickness of the main body of the hollow fiber membrane is 8%-20%, preferably 10%-15%.

[0029] Further, the thickness of the support layer is 65-100 μm, the average pore size of the support layer is 150-550 nm, and the average porosity of the support layer is 65%-90%.

[0030] It should be noted that the water vapor generally exists in the form of steam in the support layer, and the thickness, average pore size and average porosity of the support layer have a certain influence on the permeation rate and throughput of water vapor. When the average porosity of the support layer is too large, the throughput of water vapor is increased, and when the support layer has a larger average pore size, the throughput of water vapor and the permeation rate of water vapor are increased. When the average porosity of the support layer is too large, the more the holes in the membrane, which reduces the tensile strength of the membrane. When the average pore size of the support layer is too large, the hollow structure in the membrane is too much, which reduces the tensile strength of the membrane. Therefore, the appropriate thickness, average pore size and porosity of the support layer in the present application make the water vapor have a higher permeation rate and a larger throughput, while ensuring the tensile strength of the hollow fiber membrane.

[0031] Further, the average pore size of the capillary condensation layer is 20-120 nm, and the porosity of the capillary condensation layer is 15%-50%.

[0032] It should be noted that when the average pore size of the capillary condensation layer is larger, the diffusion rate of water in the flow channel is accelerated, the effect of blocking gas transmission is reduced, and the gas transmission amount is increased. When the average pore size of the capillary condensation layer is smaller, although the transmission of gas is effectively avoided, the diffusion rate of water is also reduced. Therefore, in the present application, the average pore size of the capillary condensation layer is 20-120 nm, so that the water has a good diffusion rate, and the gas transmission amount is effectively reduced. When the porosity of the capillary condensation layer is too large, although the water transmission amount is increased, the tensile strength of the membrane is reduced. When the porosity of the capillary condensation layer is too small, although the tensile strength of the membrane is increased, the water transmission amount is reduced. Therefore, in the present application, the porosity of the capillary condensation layer is 15%-50%, which ensures the water flux and guarantees the tensile strength of the membrane.

[0033] Further, the capillary condensation layer comprises a skin layer region, one side of the skin layer region is an inner surface; the thickness of the skin layer region accounts for 15%-25% of the thickness of the capillary condensation layer, and the porosity of the skin layer region is not more than 10%.

[0034] It should be noted that the skin layer region is photographed by a scanning electron microscope at 50000 times, and the porosity of the skin layer region is not more than 10%, i.e. there are two cases of unobservable pore structure and observable porosity not more than 10%.

[0035] If the skin layer region is too thick, although the tensile strength of the membrane is increased, the water vapor transmission rate is reduced, and the water conversion efficiency is reduced. If the skin layer region is thinner, although the water vapor transmission rate is increased, the overall tensile strength of the membrane is reduced. Therefore, in the present application, the thickness of the skin layer region accounts for 15%-25% of the thickness of the capillary condensation layer, so that the water vapor has a good transmission rate, the water conversion efficiency is increased, and the good tensile strength is maintained.

[0036] Further, the main body comprises fibers forming a porous structure, and the fibers are in a strip structure; the average diameter of the fibers is 200-500 nm.

[0037] In the present application, the average diameter of the fibers can be measured by using a scanning electron microscope to characterize the morphology of the hollow fiber membrane cross-section structure, and then using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement to calculate the average value. Those skilled in the art can also obtain the above-mentioned parameters by other measurement means.

[0038] The main body in the application is formed into a porous structure by strip-shaped fibers, wherein the fibers are uniformly distributed, and the average diameter of the fibers is 200-500 nm. When the average diameter of the fibers is larger, the porosity of the whole is reduced, thereby affecting the water conversion efficiency. When the average diameter of the fibers is smaller, the hollow fiber membrane has a larger hollow area ratio, thereby reducing the mechanical strength, and the hollow fiber membrane is prone to deformation when subjected to a larger pressure.

[0039] The average diameter of the fibers of the hollow fiber membrane provided in the application is 200-500 nm, which can support and protect the support layer to some extent, so that the pore structure formed by the hollow fiber membrane is more stable and not easy to collapse, has good pressure resistance, and the whole hollow fiber membrane has good tensile strength. At the same time, the hollow fiber membrane has uniform pore distribution and suitable porosity, so that the hollow fiber membrane has high water conversion efficiency.

[0040] Further, the thickness of the hollow fiber membrane is 80-150 μm, and the inner diameter of the hollow fiber is 0.7-1.2 mm.

[0041] It should be noted that the thickness and inner diameter of the hollow fiber membrane can be measured and calculated by using a scanning electron microscope to characterize the morphology of the hollow fiber membrane structure, and then using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement. The above-mentioned parameters can also be obtained by other measurement methods, and the above-mentioned measurement methods are only for reference.

[0042] When the thickness of the hollow fiber membrane is smaller, the mechanical strength of the hollow fiber membrane is reduced, and the hollow fiber membrane is prone to deformation under pressure. When the thickness of the hollow fiber membrane is larger, the time for water vapor to pass through the hollow fiber membrane is increased, resulting in excessive time cost. The thickness of the hollow fiber membrane provided in the application is 80-150 μm, which ensures that the hollow fiber membrane has high mechanical strength, high water conversion efficiency, and fast water vapor permeation speed, and low time cost.

[0043] When the inner diameter of the hollow fiber membrane is larger, the mechanical strength of the whole hollow fiber membrane is reduced, and the hollow fiber membrane is prone to deformation under a larger pressure, thereby affecting the humidification effect of the hollow fiber membrane. When the inner diameter of the hollow fiber membrane is smaller, the amount of dry air passing into the inner diameter is reduced, thereby reducing the diffusion amount of water on the inner surface of the hollow fiber membrane, resulting in water aggregation on the inner surface of the hollow fiber membrane, thereby reducing the humidification effect of the hollow fiber membrane. The hollow fiber membrane provided in the application has a suitable inner diameter, which ensures that it has sufficient mechanical strength, thereby having pressure resistance and deformation resistance. At the same time, the amount of dry air passing in satisfies the requirement, so that the water on the inner surface can be removed in time, so that the hollow fiber membrane has good humidification effect.

[0044] In summary, the inner diameter and thickness of the hollow fiber membrane of the application make the hollow fiber membrane not only have good anti-deformation effect and pressure resistance effect, but also have good humidification effect.

[0045] Further, the outer surface has a plurality of first holes in the shape of a circular hole; the hole area ratio of the first holes on the first outer surface is 12%-55%.

[0046] It should be noted that the first holes on the outer surface are in the shape of a circular hole, some of which are circular and some of which are similar to a circle, such as an oval. When the hole area ratio of the first holes on the first surface is too large, the mechanical strength of the outer surface is reduced, making the outer surface prone to breakage and poor pressure resistance; when the hole area ratio of the first holes is too small, the amount of water vapor passing through is reduced, thereby reducing the water conversion efficiency, and at the same time, the roughness of the outer surface is reduced, thereby increasing the amount of gas passing through.

[0047] The outer surface in the application has a suitable hole area ratio, which ensures the mechanical strength of the outer surface and increases the service life; at the same time, the amount of water vapor entering the hollow fiber membrane is increased, thereby improving the water conversion efficiency and reducing the amount of gas passing through.

[0048] Further, the main body further comprises a plurality of moisture-permeable holes, and the average pore size of the moisture-permeable holes is 1.8-5.2 μm, preferably 2.5-4.5 μm.

[0049] It should be noted that the number of moisture-permeable holes is small; among them, the skin layer region does not have moisture-permeable holes to avoid increasing the amount of gas passing through the hollow fiber membrane; the average pore size of the moisture-permeable holes is larger than the average pore size of the outer surface, i.e., the pore size of the moisture-permeable holes is relatively large, which improves the porosity of the hollow fiber membrane, thereby increasing the amount of water vapor passing through and further increasing the humidification efficiency of the membrane; and since the number of moisture-permeable holes is small, it does not affect the tensile strength of the membrane.

[0050] Further, the tensile strength of the hollow fiber membrane is 4-9 MPa, the elongation rate is 40%-120%, the air flux is 10-25 ml / min / m2@80KPa, the internal burst pressure is greater than 500 kpa, and the water conversion efficiency is 40%-65%.

[0051] The important index for evaluating the mechanical strength of the hollow fiber membrane is the tensile strength and the elongation at break of the hollow fiber membrane; under certain conditions, the greater the tensile strength of the hollow fiber membrane, the better the mechanical strength of the hollow fiber membrane. The tensile strength refers to the ability of the membrane to withstand parallel tensile action. When tested under certain conditions, the membrane sample is subjected to tensile load until failure, and according to the corresponding maximum tensile load and the change in the size (length) of the membrane sample at the time of failure, the tensile strength and the elongation at break of the membrane can be calculated. The tensile strength and the elongation at break can be measured by a universal tensile testing machine. The tensile strength of the filter membrane of the present application is 4-9 MPa; the elongation at break is 40-120%, and the implosion pressure is greater than 500 kPa, which indicates that the hollow fiber membrane of the present application has greater tensile strength and elongation at break, and has good pressure resistance, better mechanical properties, higher industrial practical value, and can fully meet the market demand.

[0052] The flux refers to the amount of material permeated through a unit membrane area per unit time under a certain working pressure in the separation process. The air flux of the hollow fiber membrane of the present application is 10-25 ml / min / m 2 @80 KPa, and the flux is small, indicating that the air permeation flux of the hollow fiber membrane is small; the permeation coefficient of the hollow fiber membrane provided by the present application is 0.52-0.56 g / cm 2 / MPa, and the water conversion efficiency is 40-65%, which ensures a high water conversion efficiency and a small air throughput, so that the hollow fiber membrane has a good humidifying effect.

[0053] On the other hand, a method for preparing a high-humidity-permeable and low-air-permeable hollow fiber membrane, which comprises the following steps in sequence:

[0054] S1: preparing a casting solution and a core solution; the casting solution comprises the following components by weight: 15-25 parts of a polysulfone-based polymer, 5-20 parts of a hydrophilic additive, 55-80 parts of a first organic solvent, and 1-5 parts of sulfonated polyether sulfone; the core solution comprises a second organic solvent and a non-solvent, the non-solvent being water and the content being 60%-100%.

[0055] S2: spinning, the casting solution and the core solution are simultaneously extruded from a spinning nozzle to form a shaped product having an inner surface and an outer surface.

[0056] S3: pre-phase separation, the shaped product is subjected to pre-phase separation in an air section, the humidity of the air section is 50-100%, and the pre-phase separation time is 0.1-2 s.

[0057] S4: the pre-phase separation formed product is put into a coagulation bath to be phase separated again to form a green membrane, the coagulation bath temperature is 30-60℃, the phase separation time is 15-55s, the coagulation bath is a mixture of water and a third organic solvent, the water content in the coagulation bath is 60-100%.

[0058] S5: the green membrane is stretched, washed in water and dried to obtain a hollow fiber membrane.

[0059] Preferably, the hydrophilic additive is at least one of polyethylene glycol, polyvinylpyrrolidone, polyvinyl imine and polyvinyl alcohol; the first organic solvent, the second organic solvent and the third organic solvent are at least one of dimethyl sulfoxide, dimethyl formamide, N-ethyl pyrrolidone, dimethyl acetamide and N-methyl pyrrolidone; the polysulfone polymer is at least one of polyether sulfone, polysulfone and polyaryl sulfone.

[0060] Further, in the step S1, the casting solution temperature is 30-70℃ and the core solution temperature is 20-30℃. The temperature of the spinning nozzle is the same as that of the casting solution to avoid the temperature of the spinning nozzle being too high to affect the temperature of the casting solution, which further affects the core solution temperature and the phase separation of the inner surface of the casting solution. The temperature of the die extrusion is at least 10℃ higher than the core solution temperature, and the core solution temperature is lower than the temperature of the die extrusion, which is helpful to form a dense surface on the inner surface of the membrane. If the core solution temperature is too low, the skin layer of the membrane is thick, which affects the humidifying performance of the membrane; if the core solution temperature is too high, the skin layer of the membrane is thin, which further reduces the mechanical properties of the membrane.

[0061] Further, in the step S5, the stretching rate is 3-12m / min, and the green membrane is stretched by 1-5 times.

[0062] Further, the casting solution further comprises 1-3 parts of a non-solvent, the weight of the non-solvent is not more than 4% of the weight of the first organic solvent; and the non-solvent is at least one of water, ethanol and isopropyl alcohol.

[0063] In the above method, the casting solution and the core solution are prepared, the casting solution includes a polysulfone polymer, a hydrophilic additive and a first organic solvent, wherein the hydrophilic additive is at least one of polyethylene glycol, polyvinylpyrrolidone, polyvinyl imine and polyvinyl alcohol, so as to increase the hydrophilicity of the casting solution, so that the organic solvent is more easily dissolved by the coagulation bath in the process of phase separation, so that the polysulfone is more easily precipitated, so that it is easier to form a polysulfone membrane with a small and gradiently changed pore size, and the hydrophilicity of the prepared hollow fiber membrane is increased; a small amount of sulfonated polyether sulfone is added to the casting solution to further increase the hydrophilicity of the membrane, if the content of the sulfonated polyether sulfone is too high, the mechanical strength in the film forming process will be low and brittle, and thus the tensile strength of the hollow fiber membrane is reduced. In addition, the viscosity of the casting solution can also be adjusted by adding sulfonated polyether sulfone. A small amount of non-solvent (water, ethanol, isopropyl alcohol, etc.) is added to the casting solution to make the casting solution partially turbid (a small amount of PES small particles are formed), these small particles play the role of nucleating agent in the process of phase separation, accelerate the nucleation and growth rate of the membrane, and easily form a relatively loose large pore structure, that is, the formation of a wet permeable hole. If the content of the non-solvent is too high, the number of the wet permeable holes is easily increased, the average pore size of the wet permeable holes is increased, the gas throughput of the hollow fiber membrane is increased, the mechanical strength is reduced, and thus the performance of the hollow fiber membrane is reduced.

[0064] The core liquid comprises a second organic solvent and a higher content of a non-solvent (water), and the content of water in the core liquid is 60%-100%. When the casting solution and the core liquid are simultaneously extruded from the spinning nozzle, the temperature of the spinning nozzle and the temperature of the casting solution are the same, so as to avoid the influence of the high temperature of the spinning nozzle on the temperature of the casting solution, and the temperature of the casting solution is higher than that of the core liquid, so as to accelerate the phase separation of the inner surface. In addition, since the sulfonated polyether sulfone is a water-soluble substance, according to the similar compatibility principle, the sulfonated polyether sulfone gradually moves to the core liquid, so that the content of sulfonic acid groups on the inner surface is greater than that on the outer surface, and the content of sulfonic acid groups gradually decreases from the inner surface to the outer surface, resulting in a gradual decrease in hydrophilicity from the inner surface to the outer surface. Placing the formed product with the inner and outer surfaces in a high-humidity airflow is beneficial to the formation of a structure with large pores in the region close to the outer surface and the outer surface, so that the average pore size along the thickness direction of the membrane changes in a gradient manner. The pre-phase-separated formed product is placed in a coagulation bath for re-phase separation, and the coagulation bath penetrates into the hollow fiber membrane from the outer surface to the inner surface along the thickness direction of the membrane and causes phase separation, so as to ensure that the first organic solvent is completely precipitated. The penetration amount of the coagulation bath into the inner surface of the hollow fiber membrane gradually decreases, and the penetration speed gradually slows down, so that the average pore size of the region from the outer surface of the hollow fiber membrane to the region close to the inner surface gradually decreases. The coagulation bath penetrates into the hollow fiber membrane from the pore formed on the outer surface of the pre-phase-separated product to the inside of the hollow fiber membrane, and further precipitates the first organic solvent, so as to increase the porosity of the membrane. Since the penetration speed is slower and the penetration amount is less and less, the pore size of the formed pore gradually decreases, so that the average pore size along the thickness direction of the membrane from the outer surface to the inner surface gradually decreases. Stretching the formed green membrane at a stretching rate of 3-12 m / min by 1-5 times can effectively avoid the shrinkage of the pores formed by phase separation, and play a role in shaping. At a suitable stretching rate, the pore size of the same level is relatively uniform, and a suitable stretching multiple can effectively avoid fiber breakage caused by too large stretching efficiency multiple or poor stretching effect caused by too small stretching multiple. Finally, the membrane is cleaned in water and dried to obtain a hollow fiber membrane.

[0065] In another aspect, the hollow fiber membrane is applied to a humidifier of a fuel cell, the humidifier comprising a housing and a hollow fiber membrane bundle located inside the housing, the hollow fiber membrane bundle being composed of a plurality of high-humidity-permeable and low-gas-permeable hollow fiber membranes, both ends of the hollow fiber membrane bundle being sealed by potting material to form sealing portions, and being fixed to both ends of the housing by the sealing portions, the housing having a first inlet, a first outlet, a second inlet and a second outlet, the first inlet and the first outlet being in communication with a space between the inside of the housing and the periphery of the hollow fiber membrane bundle for the first fluid to flow through, the second inlet and the second outlet being in communication with the inside of the hollow fiber for the second fluid to flow through, and the sealing portions separating the first fluid and the second fluid. The first fluid is humid gas with a high water vapor content, and the second fluid is dry gas with a low water vapor content. During the operation of the humidifier, humid gas with a high water vapor content flows in from the first inlet, enters the space between the inside of the housing and the periphery of the hollow fiber membrane bundle, the water vapor diffuses to the hollow fiber membrane bundle, and other gases in the humid gas diffuse towards the first outlet, dry gas flows in from the second inlet, enters the hollow interior of each hollow fiber, carries away the water vapor diffused to the hollow fiber membrane, and flows towards the second outlet, thereby achieving the effect of humidification.

[0066] The hollow fiber membrane provided by the present application has the advantages of good water conversion efficiency, low gas throughput and good tensile strength, and can be used for a long time at high temperature and high pressure. The performance of the hollow fiber membrane mainly composed of polysulfone polymer is greatly improved, and the service life is prolonged. The preparation method provided by the present application can conveniently, quickly and effectively prepare the above-mentioned hollow fiber membrane. BRIEF DESCRIPTION OF DRAWINGS

[0067] The accompanying drawings, which are included to provide a further understanding of the present application and are incorporated in and constitute a part of this application, illustrate embodiments of the present application and serve to explain the present application. The above brief description does not necessarily describe the only way of implementing the present application. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 A scanning electron microscope (SEM) image of the cross section of the high-humidity-permeable and low-gas-permeable hollow fiber membrane prepared in Example 1, with a magnification of 1000x;

[0070] Figure 2 A scanning electron microscope (SEM) image of the longitudinal section of the capillary condensation layer of the high-humidity-permeable and low-gas-permeable hollow fiber membrane prepared in Example 1, with a magnification of 2000x;

[0071] Figure 3 A scanning electron microscope (SEM) image of the longitudinal section of the support layer of the high-humidity-permeable and low-gas-permeable hollow fiber membrane prepared in Example 1, with a magnification of 2000x;

[0072] Figure 4 Scanning electron microscope (SEM) image of the inner surface of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 1, at a magnification of 50,000x;

[0073] Figure 5 Scanning electron microscope (SEM) image of the outer surface of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 1, at a magnification of 2,000x;

[0074] Figure 6 Scanning electron microscope (SEM) image of the cross-section of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 4, at a magnification of 1,000x;

[0075] Figure 7 Scanning electron microscope (SEM) image of the longitudinal section of the capillary condensation layer of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 4, at a magnification of 5,000x;

[0076] Figure 8 Scanning electron microscope (SEM) image of the longitudinal section of the support layer of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 4, at a magnification of 1,500x;

[0077] Figure 9 Scanning electron microscope (SEM) image of the inner surface of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 4, at a magnification of 50,000x;

[0078] Figure 10 Scanning electron microscope (SEM) image of the outer surface of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 4, at a magnification of 2,000x;

[0079] Figure 11 Scanning electron microscope (SEM) image of the longitudinal section of the capillary condensation layer of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 8, at a magnification of 5,000x;

[0080] Figure 12 Scanning electron microscope (SEM) image of the longitudinal section of the support layer of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 8, at a magnification of 5,000x;

[0081] Figure 13 Scanning electron microscope (SEM) image of the inner surface of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 8, at a magnification of 20,000x;

[0082] Figure 14 Scanning electron microscope (SEM) image of the outer surface of the high moisture permeable and low air permeable hollow fiber membrane prepared in Example 8, at a magnification of 2,000x;

[0083] Figure 15 A polysulfone hollow fiber membrane humidifier.

[0084] Reference signs:

[0085] 1. first inlet; 2. first outlet; 3. second inlet; 4. second outlet. DETAILED DESCRIPTION

[0086] In order to more clearly illustrate the overall concept of the present application, the following is described in detail in the form of examples. In the following description, a large number of specific details are given in order to provide a more thorough understanding of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced without one or more of these details. In other instances, some well-known features are not described in order not to obscure the present application.

[0087] In the following examples, the raw materials and equipment used in the preparation of the hollow fiber membrane can be purchased through commercial channels, unless otherwise specified. Among them, the structure and morphology of the filter membrane are characterized by a scanning electron microscope provided by Hitachi with a model number of S-5500.

[0088] Example 1

[0089] Example 1 provides a polysulfone hollow fiber membrane, which is prepared by the following method:

[0090] S1: preparing a casting solution and a core solution;

[0091] The casting solution includes the following components in parts by weight: polyether sulfone 15 parts, polyethylene glycol 12 parts, dimethyl sulfoxide 60 parts, and sulfonated polyether sulfone 4 parts;

[0092] The core solution includes water 90% and dimethylformamide 10%;

[0093] S2: spinning, simultaneously extruding the casting solution at a temperature of 35°C and the core solution at a temperature of 22°C from a spinning nozzle to form a shaped product having an inner surface and an outer surface; the temperature of the spinning nozzle is the same as the temperature of the casting solution;

[0094] S3: pre-phase separation, pre-phasing the shaped product in an air section with a humidity of 80% for 1s;

[0095] S4: placing the pre-phased shaped product into a coagulation bath at a temperature of 35°C for 45s of re-phase separation to form a green membrane. The coagulation bath is a mixture of water and N-methyl pyrrolidone, and the water content in the coagulation bath is 70%;

[0096] S5: stretching the green membrane by 2.5 times at a stretching rate of 5 m / min, washing in water, and finally drying to obtain a hollow fiber membrane.

[0097] Example 2

[0098] Example 2 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0099] S1: preparing casting solution and core solution;

[0100] The casting solution comprises the following components by weight: polysulfone 17 parts, polyvinylpyrrolidone 14 parts, N-ethylpyrrolidone 76 parts and sulfonated polyether sulfone 1.5 parts;

[0101] The core solution comprises N-ethylpyrrolidone 25% and water 75%;

[0102] S2: spinning, the casting solution at a temperature of 48°C and the core solution at a temperature of 23°C are simultaneously extruded from a spinning nozzle to form a shaped product having an inner surface and an outer surface, the temperature of the spinning nozzle and the temperature of the casting solution are the same;

[0103] S3: pre-phase separation, the shaped product is subjected to pre-phase separation for 0.5s in an air section with a humidity of 92%;

[0104] S4: the pre-phase separated shaped product is placed in a coagulation bath at a temperature of 55°C for 36s for re-phase separation to form a green membrane. The coagulation bath is a mixture of water and N-ethylpyrrolidone, and the water content in the coagulation bath is 75%;

[0105] S5: the green membrane is subjected to a stretching treatment at a stretching rate of 7m / min by 2.8 times, washed in water, and finally dried to obtain a hollow fiber membrane.

[0106] Example 3

[0107] Example 3 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0108] S1: preparing casting solution and core solution;

[0109] The casting solution comprises the following components by weight: polyether sulfone 16 parts, polyethylene glycol 9 parts, dimethyl sulfoxide 65 parts and sulfonated polyether sulfone 4.5 parts;

[0110] The core solution comprises water 83% and dimethylformamide 17%;

[0111] S2: spinning, the casting solution at a temperature of 43°C and the core solution at a temperature of 25°C are simultaneously extruded from a spinning nozzle to form a shaped product having an inner surface and an outer surface; the temperature of the spinning nozzle and the temperature of the casting solution are the same.

[0112] S3: pre-phase separation, the shaped product is subjected to pre-phase separation for 1.5s in an air section with a humidity of 85%;

[0113] S4: the pre-phase separation of the shaped product is put into a coagulation bath with a temperature of 40°C for 36s of re-phase separation to form a green membrane. The coagulation bath is a mixture of water and N-methyl pyrrolidone, and the water content in the coagulation bath is 75%;

[0114] S5: the green membrane is stretched by 3 times at a stretching rate of 5.6m / min, washed in water, and finally dried to obtain a hollow fiber membrane.

[0115] Example 4

[0116] Example 4 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0117] S1: preparing a casting solution and a core solution;

[0118] The casting solution comprises the following components in parts by weight: polyether sulfone 18 parts, sulfonated polyether sulfone 1 part, polyvinyl pyrrolidone 15 parts, and dimethyl formamide 70 parts;

[0119] The core solution comprises N-ethyl pyrrolidone 20% and water 80%;

[0120] S2: spinning, the casting solution with a temperature of 40°C and the core solution with a temperature of 24°C are simultaneously extruded from a spinning nozzle to form a shaped product with an inner surface and an outer surface, and the temperature of the spinning nozzle is the same as the temperature of the casting solution;

[0121] S3: pre-phase separation, the shaped product is subjected to 4s of pre-phase separation in an air section with a humidity of 70%;

[0122] S4: the pre-phase separation of the shaped product is put into a coagulation bath with a temperature of 45°C for 30s of re-phase separation to form a green membrane. The coagulation bath is a mixture of water and dimethyl formamide, and the water content in the coagulation bath is 80%;

[0123] S5: the green membrane is stretched by 3 times at a stretching rate of 8m / min, washed in water, and finally dried to obtain a hollow fiber membrane.

[0124] Example 5

[0125] Example 5 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0126] S1: preparing a casting solution and a core solution;

[0127] The casting solution comprises the following components in parts by weight: polyaryl sulfone 24 parts, polyethylene glycol 13 parts, N-methyl pyrrolidone 74 parts, and sulfonated polyether sulfone 2 parts;

[0128] The core solution comprises dimethyl sulfoxide 13% and 83% water;

[0129] S2: Spinning, the casting solution with a temperature of 38°C and the core solution with a temperature of 25°C are simultaneously extruded from a spinning nozzle to form a shaped product with an inner surface and an outer surface, the temperature of the spinning nozzle and the temperature of the casting solution are the same;

[0130] S3: Pre-phase separation, the shaped product is subjected to pre-phase separation for 5.5s in an air section with a humidity of 55%;

[0131] S4: The pre-phase separated shaped product is placed into a coagulation bath with a temperature of 43°C for 35s for re-phase separation to form a green membrane, the coagulation bath is a mixture of water and dimethyl sulfoxide, the water content in the coagulation bath is 83%;

[0132] S5: The green membrane is subjected to a stretching treatment with a stretching rate of 9m / min for 4.5 times, washed in water, and finally dried to obtain a hollow fiber membrane.

[0133] Example 6

[0134] Example 6 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0135] S1: Preparation of a casting solution and a core solution;

[0136] The casting solution comprises the following components in parts by weight: polyarylsulfone 20 parts, polyethyleneimine 18 parts, N-ethylpyrrolidone 65 parts, sulfonated polyether sulfone 2 parts;

[0137] The core solution comprises dimethylformamide 32% and water 68%;

[0138] S2: Spinning, the casting solution with a temperature of 45°C and the core solution with a temperature of 26°C are simultaneously extruded from a spinning nozzle to form a shaped product with an inner surface and an outer surface, the temperature of the spinning nozzle and the temperature of the casting solution are the same;

[0139] S3: Pre-phase separation, the shaped product is subjected to pre-phase separation for 2s in an air section with a humidity of 85%;

[0140] S4: The pre-phase separated shaped product is placed into a coagulation bath with a temperature of 50°C for 25s for re-phase separation to form a green membrane. The coagulation bath is a mixture of water and dimethylformamide, and the water content in the coagulation bath is 85%;

[0141] S5: The green membrane is subjected to a stretching treatment with a stretching rate of 10m / min for 3.5 times, washed in water, and finally dried to obtain a hollow fiber membrane.

[0142] Example 7

[0143] Example 7 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0144] S1: preparing casting solution and core solution;

[0145] The casting solution comprises the following components by weight: polyether sulfone 23 parts, sulfonated polyether sulfone 1.7 parts, polyvinyl imine 16 parts and dimethyl acetamide 67 parts;

[0146] The core solution comprises dimethyl formamide 35% and water 65%;

[0147] S2: spinning, the casting solution at a temperature of 50°C and the core solution at a temperature of 27°C are simultaneously extruded from a spinning nozzle to form a shaped product having an inner surface and an outer surface, the temperature of the spinning nozzle and the temperature of the casting solution are the same;

[0148] S3: pre-separation, the shaped product is subjected to pre-separation in an air section with a humidity of 60% for 3s;

[0149] S4: the shaped product after pre-separation is placed in a coagulation bath at 54°C for 30s for re-separation to form a green membrane. The coagulation bath is a mixture of water and dimethyl sulfoxide, and the water content in the coagulation bath is 88%;

[0150] S5: the green membrane is subjected to stretching treatment at a stretching rate of 7.3m / min for 3.8 times, washed in water, and finally dried to obtain a polysulfone hollow fiber membrane.

[0151] Example 8

[0152] Example 8 provides a polysulfone hollow fiber membrane, which is prepared by the following method:

[0153] S1: preparing casting solution and core solution;

[0154] The casting solution comprises the following components by weight: polyether sulfone 22 parts, polyvinyl alcohol 10 parts, dimethyl formamide 75 parts, water 2 parts and sulfonated polyether sulfone 3 parts;

[0155] The core solution comprises N-ethyl pyrrolidone 38% and water 62%;

[0156] S2: spinning, the casting solution at a temperature of 55°C and the core solution at a temperature of 27°C are simultaneously extruded from a spinning nozzle to form a shaped product having an inner surface and an outer surface, the temperature of the spinning nozzle and the temperature of the casting solution are the same;

[0157] S3: pre-separation, the shaped product is subjected to pre-separation in an air section with a humidity of 78% for 2.5s;

[0158] S4: the shaped product after pre-separation is placed in a coagulation bath at a temperature of 40°C for 35s for re-separation to form a green membrane. The coagulation bath is a mixture of water and N-methyl pyrrolidone, and the water content in the coagulation bath is 90%;

[0159] S5: The green membrane is stretched at a stretching rate of 6 m / min, washed in water, and dried to obtain the hollow fiber membrane.

[0160] Example 9

[0161] Example 9 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0162] S1: Preparation of casting solution and core solution;

[0163] The casting solution comprises the following components by weight: 19 parts of polysulfone, 9 parts of polyvinylpyrrolidone, 78 parts of N-ethylpyrrolidone, and 2 parts of sulfonated polyether sulfone;

[0164] The core solution comprises 40% dimethyl sulfoxide and 60% water;

[0165] S2: Spinning, the casting solution at a temperature of 60°C and the core solution at a temperature of 28°C are simultaneously extruded from a spinning nozzle to form a shaped product having an inner surface and an outer surface;

[0166] S3: Pre-dephasing, the shaped product is subjected to pre-dephasing in an air section with a humidity of 95% for 0.4 s;

[0167] S4: The pre-dephased shaped product is placed in a coagulation bath at a temperature of 48°C for 50 s to form a green membrane. The coagulation bath is a mixture of water and dimethylacetamide, and the water content in the coagulation bath is 86%;

[0168] S5: The green membrane is stretched at a stretching rate of 5.5 m / min, washed in water, and dried to obtain the hollow fiber membrane.

[0169] Example 10

[0170] As shown in Figure 15 , the hollow fiber membrane prepared in the present application is applied to a humidifier of a fuel cell, and the hollow fiber membrane bundle is composed of a plurality of high-humidity-permeable and low-gas-permeable hollow fiber membranes. During the operation of the humidifier, the humid air with a high water vapor content flows in from the first inlet 1 into the space outside the hollow fiber membrane bundle inside the shell, the water vapor diffuses to the hollow fiber membrane bundle, and the other gases in the humid air diffuse towards the direction of the first outlet 2. Dry gas flows in from the second inlet 3, enters the hollow interior of each hollow fiber, carries away the water vapor diffused to the hollow fiber membrane, and flows towards the direction of the second outlet 4, thereby achieving the humidification effect.

[0171] Comparative Example 1

[0172] Comparative Example 1 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0173] S1: preparing casting solution and core solution;

[0174] The casting solution comprises the following components by weight: polyether sulfone 15 parts, polyvinylpyrrolidone 6 parts and dimethylformamide 60 parts;

[0175] The core solution comprises water 90% and dimethylformamide 10%;

[0176] S2: spinning, the casting solution at a temperature of 35℃ and the core solution at a temperature of 22℃ are simultaneously extruded from a spinning nozzle to form a shaped product having an inner surface and an outer surface; the temperature of the spinning nozzle is the same as the temperature of the casting solution.

[0177] S3: pre-phase separation, the shaped product is subjected to pre-phase separation in an air section with a humidity of 80% for 1s;

[0178] S4: the shaped product after pre-phase separation is placed in a coagulation bath at a temperature of 35℃ for 45s for re-phase separation to form a green membrane. The coagulation bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulation bath is 70%;

[0179] S5: the green membrane is subjected to 2.5 times stretching treatment at a stretching rate of 5m / min, washed in water, and finally dried to obtain a hollow fiber membrane.

[0180] Comparative Example 1 and Example 1 have the same parameters in other steps, but no sulfonated polyether sulfone is added, which increases the first water contact angle of the inner and outer surfaces of the hollow fiber membrane, increases the hydrophobicity of the hollow fiber membrane, and leads to too low water conversion efficiency, which cannot meet the needs of practical application.

[0181] Comparative Example 2

[0182] Comparative Example 2 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0183] S1: preparing casting solution and core solution;

[0184] The casting solution comprises the following components by weight: polyether sulfone 15 parts, polyvinylpyrrolidone 6 parts and dimethylformamide 60 parts;

[0185] The core solution comprises water 90% and dimethylformamide 10%;

[0186] S2: spinning, the casting solution at a temperature of 35℃ and the core solution at a temperature of 22℃ are simultaneously extruded from a spinning nozzle to form a shaped product having an inner surface and an outer surface; the temperature of the spinning nozzle is the same as the temperature of the casting solution.

[0187] S3: pre-phase separation, the shaped product is subjected to pre-phase separation in an air section with a humidity of 80% for 1s;

[0188] S4: the pre-phase separation of the product is put into a coagulation bath with a temperature of 35℃ for 45s of re-phase separation to form a green membrane. The coagulation bath is a mixture of water and N-methyl pyrrolidone, and the water content in the coagulation bath is 70%;

[0189] S5: the green membrane is stretched at a stretching rate of 5m / min for 2.5 times, washed in water, and finally dried to obtain a hollow fiber membrane.

[0190] In the same conditions as the other steps of Example 1, the content of polyether sulfone is increased in Comparative Example 2, which increases the thickness of the skin layer region, resulting in too low water conversion efficiency to meet the actual application requirements.

[0191] Comparative Example 3

[0192] Comparative Example 3 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0193] S1: preparing a casting solution and a core solution;

[0194] The casting solution includes the following components by weight: 15 parts of polyether sulfone, 7 parts of polyethyleneimine, 60 parts of dimethyl sulfoxide, and 4 parts of sulfonated polyether sulfone;

[0195] The core solution includes 40% water and 60% dimethylformamide;

[0196] S2: spinning, the casting solution with a temperature of 35℃ and the core solution with a temperature of 22℃ are simultaneously extruded from a spinning nozzle to form a product with an inner surface and an outer surface; the temperature of the spinning nozzle is the same as the temperature of the casting solution;

[0197] S3: pre-phase separation, the product is subjected to 8s of pre-phase separation in an air section with a humidity of 100%;

[0198] S4: the pre-phase separation of the product is put into a coagulation bath with a temperature of 35℃ for 45s of re-phase separation to form a green membrane. The coagulation bath is a mixture of water and N-methyl pyrrolidone, and the water content in the coagulation bath is 70%;

[0199] S5: the green membrane is stretched at a stretching rate of 5m / min for 2.5 times, washed in water, and finally dried to obtain a hollow fiber membrane.

[0200] In the same conditions as the other steps of Example 1, the content of non-solvent in the core solution is reduced in Comparative Example 3, which increases the pore structure of the inner surface and increases the porosity of the skin layer region. The air permeability is too large to meet the actual application requirements.

[0201] Comparative Example 4

[0202] Comparative Example 4 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

[0203] S1: preparing casting solution and core solution;

[0204] The casting solution comprises the following components by weight: polyether sulfone 15 parts, polyvinyl alcohol 12 parts, dimethylacetamide 60 parts and sulfonated polyether sulfone 4 parts;

[0205] The core solution comprises water 90% and dimethylformamide 10%;

[0206] S2: spinning, extruding the casting solution at a temperature of 35°C and the core solution at a temperature of 22°C from a spinning nozzle at the same time to form a shaped product having an inner surface and an outer surface; the temperature of the spinning nozzle and the temperature of the casting solution are the same;

[0207] S3: pre-phase separation, pre-phasing the shaped product in an air section with a humidity of 35% for 0.3s;

[0208] S4: placing the pre-phased shaped product into a coagulation bath at a temperature of 35°C for 10s of re-phase separation to form a green membrane. The coagulation bath is a mixture of water and N-methyl pyrrolidone, and the water content in the coagulation bath is 40%;

[0209] S5: stretching the green membrane by 2.5 times at a stretching rate of 5m / min, washing in water, and finally drying to obtain a hollow fiber membrane.

[0210] Under the same conditions as the other steps of Example 1, the humidity of the pre-phase separation air is reduced to form a skin layer region near the outer surface area, and the average pore size of the outer surface is not greater than 100nm, the average pore size change gradient is too small, and the porosity is too low, resulting in too low water conversion rate, which cannot meet the demand of practical application.

[0211] Performance experiment

[0212] Structural characterization

[0213] The hollow fiber membranes obtained in each example and comparative example were respectively characterized in terms of longitudinal section, inner surface and outer surface morphology, thickness and average pore size of each layer in the main body, and fiber average diameter and porosity of the hollow fiber membrane. The measurement data are shown in Tables 1-2, and the morphology characterization results of Examples 1-8 are shown in Figures 1-14 .

[0214] Table 1 Characterization of the structure of each example membrane

[0215]

[0216]

[0217] Table 2 Characterization of the structure of each example hollow fiber membrane

[0218]

[0219]

[0220] I. Performance test

[0221] The tensile property of the hollow fiber membrane obtained in each example was tested.

[0222] Experimental equipment: tensile testing machine

[0223] Preparation before testing: the hollow fiber membrane to be tested was cut to 10 cm long.

[0224] Test steps: the membrane filament was clamped vertically on the lower and upper ends of the chuck, and the distance between the two ends of the chuck was controlled to be 5 cm. The mode was selected on the operating instrument, and the tensile strength and elongation were obtained by operating the instrument.

[0225] Result calculation: tensile strength:

[0226] In the formula: σ - tensile strength, unit: megapascal (MPa); Fb - the maximum force borne when broken, unit: (N); So - the original cross-sectional area of the sample, unit: (mm 2 ); "sample area S" is used in the instrument.

[0227] Elongation:

[0228] In the formula: e - elongation; ΔL - the increment of the length between the gauges of the sample, unit: millimeter (mm); L - the gauge of the sample, unit: millimeter (mm).

[0229] Table 3: tensile property test results of each example

[0230]

[0231]

[0232] It should be noted that the same sample has multiple test points, and the results are the average of multiple test points, and there is non-uniformity, so the point values corresponding to each test point may be different.

[0233] The inner and outer surface contact angles of the hollow fiber membrane obtained in each example were tested.

[0234] Experimental equipment: contact angle tester

[0235] Preparation before testing: a small section of the hollow fiber membrane filament was taken and cut open, and the cut open hollow fiber membrane filament was flattened and fixed on the double-sided tape.

[0236] Test procedure: The fixed hollow fiber membrane is placed on the fixture of the contact angle tester, and the change of the contact angle is observed by the change of the pure water droplet on the hollow fiber membrane, and the data of the first water contact angle is obtained.

[0237] The water conversion efficiency of each example obtained hollow fiber membrane is tested.

[0238] Experimental equipment: digital pressure gauge, gas flow meter, digital temperature and humidity meter

[0239] Preparation before testing: self-made hollow fiber subassembly

[0240] Test procedure: The self-made hollow fiber subassembly is fixed on the test bench, and a certain flow of humid air enters from the wet in end, and is monitored by the digital temperature and humidity meter, wherein the humidity needs to be controlled at 90% RH-96% RH.

[0241] Another certain flow of dry air enters from the dry in end, and is monitored by the digital temperature and humidity meter. The dry out end and the wet out end are monitored by the digital temperature and humidity meter respectively, and the humidification effect is observed.

[0242] By changing the gas flow size of the dry in end and the wet in end, different humidification data is obtained.

[0243] By installing a one-way pressure relief valve at the dry out end outlet to increase the pressure of the dry flow, different humidification data is obtained.

[0244] Calculation results:

[0245] In the formula: D-the density of dry gas or wet vapor, unit (g / m 3 ), K1, K2-constant, T-the temperature of the hollow fiber membrane dry in end, dry out end, wet in end or wet out end, unit (℃), RH)-humidity of the hollow fiber membrane dry in end, dry out end, wet in end or wet out end, unit (%).

[0246] V=Q*H

[0247] In the formula: V-the volume of dry gas or wet vapor gas, unit (m 3 ), Q-the volumetric flow of dry gas or wet vapor gas, unit (m 3 / h), H-gas flow time, unit h.

[0248] m=ρ*v

[0249] Wherein: m—water content of the hollow fiber membrane dry out end or the hollow fiber membrane wet in end, unit (g), p—density of dry gas or wet vapor, unit (g / m 3 ) v—volume of dry gas or wet vapor gas, unit (m 3 ).

[0250]

[0251] Wherein: ω—water conversion efficiency, m1—water content of the hollow fiber membrane dry out end, unit (g), m2—water content of the hollow fiber membrane wet in end, unit (g).

[0252] Air permeability test of the hollow fiber membrane obtained in each example

[0253] Experimental equipment: gas flow meter

[0254] Preparation before test: self-made hollow fiber small assembly

[0255] Test steps: block the wet out end and the dry out end of the self-made single hollow fiber membrane filament small assembly. Pass compressed air from the wet in end, and ensure that the wet in end digital pressure display value is stable at 80 kpa. Connect the digital gas flow meter at the dry in end to determine the air permeability size. (In the case of very small gas permeability, the number of bubbles can be counted within a certain time) Record the data.

[0256] Table 4: test results of hydrophilicity, water conversion efficiency and air permeability of each example

[0257]

[0258] The above only describes the embodiments of the present application and is not used to limit the present application. The present application can have various changes and variations for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the scope of claims of the present application.

Claims

1. A high moisture permeability and low air permeability 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 average aperture of the main body varies in a gradient from the region near the outer surface to the region near the inner surface. The main body includes a capillary condensation layer and a support layer, with one side of the capillary condensation layer being the inner surface and one side of the support layer being the outer surface; The other side of the capillary condensation layer and the other side of the support layer are transitioned by continuous fibers; The average pore size of the outer surface is 200-650 nm; the inner surface is a dense surface. The average pore size variation gradient of the hollow fiber membrane is 2-8 nm / μm; The first water contact angle of the inner surface is 8-35° smaller than the first water contact angle of the outer surface; The first water contact angle of the outer surface is 60-89°; Furthermore, the first water contact angle varies in a gradient from the inner surface to the outer surface film thickness direction.

2. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The porosity of the hollow fiber membrane is 60%-85%.

3. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The first water contact angle of the inner surface is 12-32° smaller than the first water contact angle of the outer surface.

4. The high moisture permeability and low air permeability hollow fiber membrane according to claim 3, characterized in that, The first water contact angle of the inner surface is 15-28° smaller than the first water contact angle of the outer surface.

5. The high moisture permeability and low air permeability hollow fiber membrane according to claim 3, characterized in that, The first water contact angle of the inner surface is 45-75°.

6. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The thickness of the capillary condensation layer is 8-25 μm, accounting for 8%-20% of the thickness of the hollow fiber membrane body.

7. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The thickness of the support layer is 65-100μm, the average pore size of the support layer is 150-550nm, and the average porosity of the support layer is 65%-90%.

8. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The average pore size of the capillary condensation layer is 20-120 nm, and the porosity of the capillary condensation layer is 15%-50%.

9. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The capillary condensation layer includes a skin region, one side of which is an inner surface; The thickness of the cortical region accounts for 15%-25% of the thickness of the capillary condensation layer, and the porosity of the cortical region does not exceed 10%.

10. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The main body includes fibers forming a porous structure, the fibers being strip-shaped; The average diameter of the fiber is 200-500 nm.

11. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The thickness of the hollow fiber membrane is 80-150 μm, and the inner diameter of the hollow fiber is 0.7-1.2 mm.

12. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The outer surface has a plurality of circular holes; the area ratio of the holes on the outer surface is 12%-55%.

13. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The main body also includes a number of moisture-permeable pores, the average pore diameter of which is 1.8-5.2 μm.

14. The high moisture permeability and low air permeability hollow fiber membrane according to claim 1, characterized in that, The air permeability of the hollow fiber membrane is 10-25 ml / min / m. 2 @80KPa, internal explosion pressure greater than 500kPa, water conversion efficiency of 40%-65%, tensile strength of 4-9MPa, elongation of 40%-120%.

15. The method for preparing a high moisture permeability and low air permeability 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: 15-25 parts of polysulfone polymer, 5-20 parts of hydrophilic additive, 55-80 parts of first organic solvent and 1-5 parts of sulfonated polyethersulfone. The core fluid includes a second organic solvent and a non-solvent, wherein the non-solvent is water and its content is 60%-100%; 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 passed through an air section for pre-phase separation, the humidity of the air section is 50%-100%, and the pre-phase separation time is 0.1-6s; 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 30-60℃, 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 60%-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 further includes 1-3 parts of non-solvent, wherein the weight of the non-solvent does not exceed 4% of the weight of the first organic solvent; the non-solvent is at least one of water, ethanol and isopropanol.

17. The preparation method according to claim 15, characterized in that, The hydrophilic additive is at least one of polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, and polyvinyl alcohol; 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, and N-methylpyrrolidone; The polysulfone polymer is at least one of polyethersulfone, polysulfone, and polyarylsulfone.

18. The preparation method according to claim 15, characterized in that, In step S1, the temperature of the casting solution is 30-70℃ and the core solution temperature is 20-30℃. In step S2, the temperature of the spinning nozzle is the same as the temperature of the casting solution, and the die extrusion temperature is at least 10℃ higher than the core solution temperature.

19. The preparation method according to claim 15, characterized in that, In step S5, the stretching rate is 3-12 m / min, and the film is stretched 1-5 times.

20. The use of the high moisture permeability and low air permeability hollow fiber membrane according to any one of claims 1-14, characterized in that, The hollow fiber membrane is used in a humidifier for a fuel cell. The humidifier includes a shell and a hollow fiber membrane bundle located inside the shell. The hollow fiber membrane bundle is composed of multiple high moisture permeability and low air permeability hollow fiber membranes according to any one of claims 1-14. The two ends of the hollow fiber membrane bundle are respectively sealed by potting material and sealed and fixed to the two ends of the shell by each of the sealing parts. The shell has a first inlet (1), a first outlet (2), a second inlet (3), and a second outlet (4). The first inlet (1) and the first outlet (2) are connected to the space between the inside of the shell and the outer periphery of the hollow fiber membrane bundle for the passage of a first fluid. The second inlet (3) and the second outlet (4) are connected to the inside of the hollow fiber for the passage of a second fluid. The sealing part separates the first fluid and the second fluid.

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