CN115845631A

CN115845631A - Moisture-permeable asymmetric hollow fiber membrane and preparation method thereof

Info

Publication number: CN115845631A
Application number: CN202211403913.9A
Authority: CN
Inventors: 贾建东; 黄盛�; 杨印景; 周鑫权
Original assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Current assignee: Hangzhou Cobetter Filtration Equipment Co Ltd
Priority date: 2022-11-10
Filing date: 2022-11-10
Publication date: 2023-03-28

Abstract

The invention relates to the technical field of moisture permeable membrane materials, and provides a moisture permeable asymmetric hollow fiber membrane and a preparation method thereof. The moisture permeable asymmetric hollow fiber membrane comprises a main body, wherein a non-directional tortuous passage is arranged in the main body, one side surface of the main body is an outer surface, the other side surface of the main body is an inner surface, the main body comprises a protective layer, a porous layer and a condensation layer, and the protective layer, the porous layer and the condensation layer are sequentially connected through continuous fibers; one side of the protective layer is an outer surface, one side of the condensation layer is an inner surface, the average pore diameter of the porous layer is larger than that of the protective layer, and the average pore diameter of the protective layer is larger than that of the condensation layer; the average pore diameter of the outer surface is 80-250nm; the average pore diameter of the inner surface is 10-60nm; the water conversion efficiency of the hollow fiber membrane is 45-65%. The polysulfone hollow fiber membrane provided by the application has high water conversion efficiency, low gas throughput and better tensile strength.

Description

Moisture-permeable asymmetric hollow fiber membrane and preparation method thereof

Technical Field

The invention relates to the technical field of moisture permeable membrane materials, in particular to a moisture permeable asymmetric hollow fiber membrane and a preparation method thereof.

Background

Asymmetric membranes are films whose chemical or physical structure varies from one membrane site to another, i.e., anisotropic films. The asymmetric membrane causes a supporting bottom layer composed of a very thin compact skin layer and a spongy or finger-like microporous layer much thicker than the skin layer to jointly form a membrane having a separation function, and exhibits asymmetry in the thickness direction of the membrane.

The hollow fiber gas separation membrane comprises a moisture permeable hollow fiber membrane, is mainly applied to a humidifier, generally has good hydrophilicity and selective permeability, separates water vapor in air from other gas components, and transmits the water vapor from the side with high humidity to the side with low humidity through the membrane.

JP2011067812a, published by japan dongli corporation in 2011, provides a water vapor permeable membrane suitable for use in a humidifier of a fuel cell system. The membrane has a compact layer and a supporting layer, the gap of the membrane is gradually reduced from the supporting layer to the compact layer, and the membrane has an asymmetric gradient pore structure, although the membrane has moisture permeability, the driving force is gradually reduced along with the gradual reduction of the pore diameter inside the membrane, so that the water vapor transmission rate is lower, and the supporting layer has a porous structure, so that the membrane has lower mechanical strength.

Therefore, it is necessary for those skilled in the art to prepare a moisture-permeable asymmetric hollow fiber membrane having a high water vapor transmission rate and strong mechanical properties.

Disclosure of Invention

In order to solve the above problems, the present invention aims to provide a moisture-permeable asymmetric hollow fiber membrane and a method for preparing the same. The hollow fiber membrane can show higher water conversion efficiency and high tensile strength, greatly improves the performance of the hollow fiber membrane taking the sulfone polymer as a main material, and prolongs the service life of the hollow fiber membrane.

In order to achieve the purpose, the invention provides the following technical scheme:

a moisture permeable asymmetric hollow fiber membrane comprises a main body, wherein a non-directional tortuous passage is formed in the main body, one side surface of the main body is an outer surface, the other side surface of the main body is an inner surface, the main body comprises a protective layer, a porous layer and a condensation layer, and the protective layer, the porous layer and the condensation layer are sequentially connected through continuous fibers; the protective layer side is the outer surface, the condensation layer side is the inner surface, the average pore size of the porous layer is larger than the average pore size of the protective layer, and the average pore size of the protective layer is larger than the average pore size of the condensation layer; the average pore diameter of the outer surface is 80-250nm; the average pore diameter of the inner surface is 10-60nm; the water conversion efficiency of the hollow fiber membrane is 45-65%.

It should be noted that the "non-directional tortuous paths" are randomly oriented groove structures and/or discretely distributed hole structures, and the non-directional tortuous paths are communicated with each other. The condensation layer is a region where water vapor is converted from vapor to liquid. The porous layer is a region where water vapor permeates into the hollow fiber membrane and flows through in a laminar flow. The protective layer is a region where water vapor permeates into the hollow fiber membrane and flows through in a turbulent flow manner. By "continuous fibers are understood fibers" integrally formed "between the protective layer, the porous layer and the condensation layer, which fibers are present in the form of an integral continuous connection without additional adhesive bonding, and which fibers cannot be separated from one another unless torn by an external force. The water vapor in the wet air passes through the membrane holes in the protective layer in a turbulent flow mode, the water vapor close to the outer surface enters the protective layer through the membrane holes and flows in the protective layer flow channel in the turbulent flow mode, the mass transfer resistance of the water vapor is mainly the collision of water vapor molecules and the walls of the membrane holes, and the transmission rate of the water vapor is gradually reduced; when the water vapor gradually enters the porous layer, the water vapor generates convection and mainly passes through the flow channel in a laminar flow flowing mode, the permeation rate of the water vapor is gradually increased along with the gradual increase of the pore diameter of the membrane, the flow of the water vapor is further increased, and meanwhile, the water vapor is gathered on the porous layer (the phenomenon that a large amount of water vapor flows to the condensation layer and the mass transfer resistance is increased) is avoided.

Steam flows to the condensation layer gradually again, and steam is in the infiltration process because the membrane aperture diminishes gradually, and steam can condense into liquid water, gets into the condensation layer promptly, and at this moment, the hollow fiber membrane is close to the concentration of the regional water of internal surface and is greater than the concentration of the water on the internal surface, forms the concentration difference, and water is by the high concentration to the low concentration diffusion, and water is by being close to near the regional diffusion to the internal surface always promptly. The dry air in the inner cavity of the hollow fiber membrane takes away the moisture diffused to the inner surface, so that the humidity of the air in the inner cavity is increased, and the humidifying function is achieved; meanwhile, when the water vapor is condensed into water in the condensation layer, the water blocks the flow channel close to the inner surface area, so that other gases can be effectively prevented from passing through, and the gas throughput is reduced.

In addition, in the operation process of the humidifying membrane component, the pressure of external wet air can reach 1.5 kilograms (150 KPa) or even higher, the porosity of the protective layer is smaller, when the wet air impacts, the generated deformation is smaller, the long-time use of the membrane wire is facilitated, the amount of water vapor entering the inside of the membrane is reduced due to the small porosity, the concentration difference of water outside and inside the membrane is facilitated to be maintained, the concentration of the area close to the interface of the membrane is prevented from being higher and higher, and the concentration polarization is reduced to a certain extent. Concentration polarization means that in the separation process, solution in the feed liquid permeates through the membrane under the drive of pressure, solute is intercepted, and the concentration of the solute is higher and higher at the interface of the membrane and the bulk solution or in the area close to the interface of the membrane; under the action of the concentration gradient, solute can diffuse from the membrane to the bulk solution to form a boundary layer, so that the fluid resistance and the local osmotic pressure are increased, and the solvent permeation quantity is reduced.

The average pore diameter of the outer surface is 80-250nm, when the average pore diameter of the outer surface is too large, the mechanical strength of the outer surface is reduced, and when the membrane is subjected to too large pressure, holes close to the outer surface area are easy to collapse, so that the membrane is deformed or broken, and the performance of the membrane is further influenced; and when the average pore diameter of the outer surface is too large, the amount of gas entering the hollow fiber membrane through the outer surface is increased, thereby increasing the amount of gas permeating the hollow fiber membrane. When the average pore size of the outer surface is small, the throughput of water vapor is reduced, thereby affecting the water conversion efficiency. The outer surface of the hollow fiber membrane prepared by the application has a proper average pore diameter, and when the hollow fiber membrane is impacted by wet air, the generated deformation is small, so that the membrane wire can be used for a long time, the throughput of water vapor is ensured, the throughput of gas is reduced, and the mechanical strength of the outer surface is also met.

The average pore diameter of the inner surface is 10-60nm, when the average pore diameter of the inner surface is too small, water is easily accumulated in the inner surface area and cannot be discharged in time, the accumulated water is easily diffused into the membrane, and the water conversion efficiency is reduced; when the average pore size of the inner surface is larger, the water liquefied by the water vapor in the condensation layer is easy to vaporize and reform into the water vapor in the area close to the outer surface, and the diffusion rate of the water vapor to the inner surface is slower, so that the water conversion efficiency is reduced. The inner surface of the condenser has a proper average pore diameter, so that the speed of moisture entering the inner cavity is increased, the flow speed of the moisture close to the inner surface is increased, the moisture almost occupies a flow channel of a condensation layer, and the throughput of gas is effectively reduced; and simultaneously, the diffusion speed of the water to the inner surface of the hollow fiber membrane is increased. Wherein, the measurement mode of the average pore diameter of the inner surface and the outer surface of the membrane can be characterized by using a scanning electron microscope, then utilizing computer software (such as Matlab, NIS-Elements and the like) or manual measurement and carrying out corresponding calculation, and in the preparation process of the membrane, the characteristics such as the pore diameter distribution are approximately uniform and basically kept consistent in the direction vertical to the membrane thickness direction (if the membrane is in a flat membrane shape, the direction is a plane direction; if the membrane is in a hollow fiber membrane shape, the direction is vertical to a radius direction); the average pore size of the whole of the plane can be reflected by the average pore size of a partial region on the corresponding plane. In practice, the surface of the membrane can be characterized by an electron microscope to obtain a corresponding SEM image, and since the pores on the surface of the membrane are substantially uniform, a certain area, such as 1 μm, can be selected ² (1 μm by 1 μm) or 25 μm ² (5 μm multiplied by 5 μm), the specific area size is determined according to the actual situation, the pore diameters of all pores on the area are measured by corresponding computer software or manually, and then the calculation is carried out to obtain the average pore diameter of the surface; of course, the skilled person can also obtain the above parameters by other measuring means, which are only used as reference.

The area rate of the holes on the outer surface is 8-15%, and the area rate of the holes on the inner surface is 0.5-5%; the ratio of the average pore diameter of the outer surface to the average pore diameter of the inner surface is 2-8.

In the application, the area rate of the holes on the outer surface is 8-15%, if the area rate of the holes is larger, the amount of water vapor entering the film is larger, so that concentration difference is formed between the inside and the outside of the film, concentration polarization is increased, water conversion efficiency is reduced, and the mechanical property of the outer surface is reduced; if the area ratio of the holes is smaller, the amount of water vapor entering the membrane is smaller, and the water conversion efficiency of the membrane is further reduced.

The area rate of the holes on the inner surface is 0.5% -5%, and if the area rate of the holes is small, the diffusion rate of water to the outside of the membrane is slow, and the water is easy to gather on the inner surface, so that the water conversion efficiency is reduced. The ratio of the average pore diameter of the outer surface to the average pore diameter of the inner surface is 2-8, if the ratio is larger, water close to the inner surface area cannot enter the inner cavity of the hollow fiber membrane from the inner surface in time, so that water vapor is retained in the membrane, and the water conversion efficiency of the membrane is reduced; if the ratio is smaller, the average pore diameter of the inner surface is larger, so that the speed of water in the membrane entering the inner cavity of the hollow fiber is higher, and the amount of gas penetrating the inner surface is increased.

Still further, the roughness of the outer surface is 10-30 μm; the roughness of the inner surface is 5-20 μm; and the roughness of the outer surface is greater than the roughness of the inner surface.

The influence of roughness on the wettability of the membrane surface is great, the inner surface and the outer surface of the membrane in the application are non-smooth planes with certain roughness, the real contact area between solid and liquid on the rough surface is larger than the apparent contact area, the wettability of the solid surface can be amplified, namely, the increase of the roughness can increase the hydrophilicity of the membrane surface, promote water vapor to enter the membrane, and improve the water conversion efficiency of the membrane. The inner surface and the outer surface have proper roughness, wherein the roughness of the outer surface is 10-30 mu m, and the roughness of the inner surface is 5-20 mu m; the outer surface has relatively large roughness and hydrophilicity, and when wet air passes through the outer surface, water vapor is promoted to enter the membrane, so that the water conversion efficiency is improved; simultaneous gas (O) ₂ And N ₂ Etc.) tend to adhere to the more rough outer surface, thereby reducing gas throughput. The roughness of the inner surface being less than that of the outer surfaceThe roughness, namely the inner surface is smoother than the outer surface, and the purging gas is introduced into the inner cavity of the hollow fiber membrane, so that the gas is prevented from being adsorbed on the inner surface to block holes on the inner surface, water cannot be diffused out of the membrane, and the water conversion efficiency is reduced; meanwhile, when the gas blows through the inner surface, the energy loss is small, and therefore the pressure drop is small. Pressure drop (pressure drop) is a change in energy. The pressure drop due to energy loss when the gas flows in the tube. This energy loss is caused by the gas flow overcoming internal friction and the gas flow exchanging momentum by the collision of gas particles, which is a pressure difference, i.e. a pressure drop, before and after the gas flow.

Still further, the average pore diameter of the protective layer is 150-350nm, the thickness of the protective layer is 3-10 μm, and the thickness of the protective layer is 3% -10% of the thickness of the hollow fiber.

The average pore diameter of the protective layer is 150-350nm, and when the average pore diameter is larger, the amount of water vapor entering the protective layer is increased instantly, so that the water vapor inside and outside the film has larger concentration difference, concentration polarization is easy to form, the water vapor is diffused from the inside to the outside of the film, the water conversion efficiency is reduced, the deformation resistance of the protective layer is reduced, and the service life of the film is further shortened; when the average pore diameter is small, the amount of water vapor passing through the protective layer decreases, thereby decreasing the water conversion efficiency.

The thickness of the protective layer is 3-10 μm, the thickness of the protective layer is 3% -10% of the thickness of the hollow fiber, when the protective layer is thicker, the percentage of the protective layer in the hollow fiber membrane is increased, the porosity of the hollow fiber membrane is reduced, and the throughput of water vapor is further reduced; when the protective layer is thin, the percentage of the protective layer in the hollow fiber membrane is small, so that the deformation resistance of the hollow fiber membrane in the area close to the outer surface is reduced, and the mechanical performance of the hollow fiber membrane is further reduced. The application has suitable protective layer thickness, and the protective layer accounts for comparatively suitable in hollow fiber membrane percentage simultaneously, makes hollow fiber membrane have higher steam throughput and better mechanical properties.

Still further, the porosity of the protective layer is 30-60%, the fibers forming the porous structure in the protective layer are strip-shaped first fibers, and the average diameter of the first fibers is 80-150nm.

The first fibers forming the porous structure in the protective layer are strip-shaped, specifically columnar bodies, and the average diameter of the first fibers is 80-150nm, so that the protective layer has proper tensile strength, pore size and porosity. When the average diameter of the first fiber is larger, the average pore diameter of the porous structure of the protective layer is reduced, so that the collision between water vapor molecules and the membrane pore wall is more frequent, the mass transfer resistance of the water vapor is increased, and meanwhile, the porosity of the protective layer is reduced, so that the porosity of the hollow fiber is reduced, and the passing rate and the throughput of the water vapor are reduced; when the average diameter of the first fiber is smaller, the mechanical strength of the first fiber is reduced, the mechanical strength of the hollow fiber membrane is further reduced, the average pore diameter and porosity of the protective layer are increased, the mass transfer resistance of water vapor is reduced, the instantaneous throughput of the water vapor is increased, the concentration polarization of the water vapor inside and outside the membrane is further increased, the water vapor performs back diffusion, and the throughput of the water vapor of the hollow fiber membrane is reduced. The first fiber has proper average diameter, the protecting layer has proper mechanical strength, porosity and average pore size, and the hollow fiber membrane has proper mass transfer resistance and proper water vapor passing amount.

Still further, the first water contact angle of the outer surface is 65-87 °, and the difference between the first water contact angle of the outer surface and the first water contact angle of the inner surface is 10-35 °.

It is noted that when the first water contact angle of the inner surface is small, the hydrophilicity of the inner surface is large, which causes water to collect in the region of the inner surface near the membrane, thereby reducing the rate of water diffusion. When the first water contact angle of the inner surface is too large, the hydrophilicity of the area close to the inner surface is smaller, so that the water flowing speed in the flow channel close to the inner surface area is reduced, and the diffusion rate of water is further reduced. The inner surface of the hollow fiber membrane has a proper first water contact angle, so that water in the hollow fiber membrane flows to the inner surface at a proper flow speed, and the water on the inner surface is not gathered, and the humidifying effect of the membrane is further increased. When the water contact angle of the outer surface is too large, the hydrophobicity of the area close to the outer surface is larger, so that the amount of water vapor entering the area of the outer surface is reduced. When surface water contact angle is less, the hydrophilicity that is close to the surface zone is great, is unfavorable for the inside surface diffusion of vapor, and then reduces the throughput of vapor, and this application surface has suitable first water contact angle, makes vapor in time pass through the surface, effectively avoids vapor to gather in surface zone outside, helps improving hollow fiber membrane's water conversion efficiency.

Still further, the porous layer has an average pore size of 250 to 650nm; the thickness of the porous layer is 65-120 μm, and the thickness of the porous layer accounts for 65% -80% of the thickness of the hollow fiber membrane; the thickness of the porous layer is 60-110 μm greater than that of the protective layer.

The porous layer of this application has suitable average pore size, makes steam pass through in the porous layer with laminar flow flowing mode, increases the permeation rate of steam, avoids steam to concentrate in the protective layer and increases concentration polarization. If the average pore diameter of the porous layer is too large, the tensile strength of the hollow fiber membrane is reduced, meanwhile, the passing rate of water vapor in the porous layer is increased, a large amount of water vapor flows to the condensation layer, the water vapor is easily gathered in the condensation layer to block the pores, the water vapor is subjected to back diffusion, and the water conversion efficiency of the hollow fiber membrane is reduced; if the average pore size of the porous layer is small, the flow rate of water vapor is reduced, thereby reducing the amount of water vapor passing through the hollow fiber membranes.

The thickness of the porous layer is 65-120 mu m, the thickness of the porous layer accounts for 65% -80% of the thickness of the hollow fiber membrane, and when the porous layer is thicker, the percentage of the hollow fiber membrane is larger, so that the porosity of the hollow fiber membrane is increased, and the tensile strength of the membrane is reduced; when the porous layer is thin, the percentage of the hollow fiber membrane is small, the porosity of the hollow fiber membrane is reduced, the speed of water vapor penetrating through the hollow fiber membrane is reduced, and further the penetration of the water vapor is reduced.

The difference between the thickness of the porous layer and the thickness of the protective layer is proper, so that water vapor has high transmission rate, the hollow fiber membrane has high tensile strength, and the hollow fiber membrane has proper porosity. If the difference between the thickness of the porous layer and the thickness of the protective layer is smaller, the porosity of the hollow fiber is reduced, the water vapor transmission rate is reduced, and the water vapor transmission amount is reduced; if the difference between the thickness of the porous layer and the thickness of the protective layer is large, the porosity of the hollow fiber membrane increases, and the tensile strength decreases.

Still further, the average pore diameter of the porous layer is 1.4 to 2.5 times the average pore diameter of the protective layer; the porosity of the porous layer is 55-85%, the fibers forming the porous structure in the porous layer are strip-shaped second fibers, and the average diameter of the second fibers is 130-180nm; the ratio of the average diameter of the second fibers to the average diameter of the first fibers is 1.2 to 1.8.

In the application, the second fibers forming a porous structure in the porous layer are strip-shaped, the average diameter of the second fibers is 130-180nm, so that the porous layer has proper porosity, pore diameter and the like, if the diameter of the second fibers is larger, the average pore diameter of the porous layer is smaller, water vapor flows in the porous layer in a mode of coexistence of turbulent flow or turbulent flow and laminar flow, the passing speed reduction rate of the water vapor is reduced, meanwhile, the porosity of the hollow fiber membrane is reduced, and further, the passing amount of the water vapor in the hollow fiber membrane is reduced; if the diameter of the second fiber is smaller, the average pore diameter of the porous layer is increased, so that the passing rate of the water vapor is increased, the water vapor is easy to gather and block the pores, the water vapor is diffused reversely, the passing amount of the water vapor is reduced, meanwhile, the tensile strength of the hollow fiber membrane is reduced, and the average diameter of the second fiber is proper, so that the porous layer has proper porosity, and the hollow fiber membrane has proper tensile strength and water vapor passing amount; in the application, the ratio of the average diameter of the second fibers to the average diameter of the first fibers is proper, so that the hollow fiber membrane has higher tensile strength, the protective layer and the porous layer have proper average pore diameters, the average pore diameter of the porous layer is 1.4-2.5 times of the average pore diameter of the protective layer, and water vapor flows through the protective layer and the porous layer in a proper mode and at a proper speed, so that concentration polarization is reduced, the water vapor throughput is increased, and the water conversion efficiency of the hollow fiber membrane is further increased.

Still further, the thickness of the condensation layer is 5-20 μm, and the thickness of the condensation layer accounts for 8% -15% of the thickness of the hollow fiber membrane.

It should be noted that the thickness of the condensation layer as a percentage of the hollow fiber membrane thickness in the present application determines the water conversion efficiency and gas throughput. When the percentage is large, the condensation layer is thick, so that the diffusion speed of water condensed by water vapor in the hollow fiber membrane is slow, and the throughput of the water vapor is reduced. When the percentage is too small, the condensation layer is thin, and although the diffusion speed of the water condensed by the water vapor in the hollow fiber membrane is accelerated, the gas blocking effect is reduced along with the acceleration of the flow speed of the water in the flow channel, so that the throughput of the gas is increased. Therefore, the proper thickness of the condensation layer and the percentage of the condensation layer in the thickness of the hollow fiber membrane are beneficial to improving the conversion efficiency of water, and simultaneously, the permeation of gas is effectively avoided.

Still further, the average pore diameter of the area of the condensation layer close to one side of the porous layer is reduced in a gradient manner towards the area of one side of the inner surface, the average pore diameter of the condensation layer is 40-140nm, and the porosity of the condensation layer is 15% -50%.

It should be noted that the average pore diameter of the area of the condensation layer close to the porous layer decreases in a gradient manner towards the area of the inner surface, which is beneficial to the liquefaction of water vapor into water in the condensation layer, and when the average pore diameter of the condensation layer is larger, the diffusion rate of water in the flow channel is accelerated, the effect of blocking gas permeation is reduced, and further the gas throughput is increased. When the average pore diameter of the condensation layer is small, gas permeation is effectively avoided, and the diffusion rate of water is reduced. Therefore, the average pore diameter of the condensation layer is 40-140nm, so that the water has a better diffusion rate, and the gas throughput is effectively reduced. When the porosity of the condensation layer is too large, the tensile strength of the film is reduced although the water passage is increased. When the porosity of the condensation layer is too small, the tensile strength of the film is increased, but the throughput of water is decreased. Therefore, the porosity of the condensation layer is 15% -50%, and the tensile strength of the membrane is guaranteed while the water flux is guaranteed.

Still further, the condensation layer is provided with a skin layer area, one side of the skin layer area is an inner surface, and the thickness of the skin layer area accounts for 2% -10% of the thickness of the condensation layer; the skin region has a porosity of no greater than 10%.

The skin layer area is shot by a scanning electron microscope at 50000 times, the porosity of the skin layer area is not more than 10%, namely, two conditions that the pore structure cannot be observed and the porosity of the pores can be observed is not more than 10% exist.

Wherein if the skin region is too thick, the tensile strength of the film is increased, but the permeation rate of water vapor is decreased, thereby decreasing the water conversion efficiency. If the sheath region is thin, although the water vapor transmission rate is increased, the tensile strength of the hollow fiber membrane as a whole is reduced. Therefore, the thickness of the skin layer area accounts for 2% -10% of the thickness of the condensation layer, so that water vapor has a good permeation rate, the water conversion efficiency is increased, and meanwhile, good tensile strength is kept.

Still further, the average pore diameter of the porous layer decreases in a gradient from a region on the side close to the protective layer to a region on the side close to the condensation layer, and the average pore diameter of the porous layer changes in a gradient of 4 to 8nm/um.

It should be noted that, the average pore diameter of the porous layer close to the protective layer area is larger, the passing rate of the water vapor entering the porous layer is instantly increased, so that the throughput of the water vapor is increased, the average pore diameter of the porous layer is gradually reduced towards the condensation layer, the water vapor is gradually circulated towards the condensation layer by the gradient change of 4-8nm/um, and the circulation speed of the water vapor is gradually reduced along with the gradual reduction of the average pore diameter, so as to avoid the water vapor from converging and blocking the pores. If the gradient change is large, the passing rate of the water vapor entering the porous layer is increased instantly, and the water vapor entering the porous layer cannot flow into the condensation layer in time, so that the water vapor is gathered in the porous layer to block the holes, the throughput of the water vapor is reduced, and the water conversion efficiency is further reduced; if the gradient change is small, the circulation speed of the water vapor in the porous layer is high, the water vapor is easy to gather in the condensation layer to block the holes, and the water conversion efficiency is reduced. The method has a proper average pore diameter change gradient, effectively avoids water vapor accumulation to reduce the water conversion efficiency, and simultaneously increases the throughput of the water vapor.

Still further, the average pore diameter of the porous layer is increased and then decreased from the area close to the protective layer to the area close to the condensation layer; the area of the porous layer with increased average pore diameter is the area with increased pore diameter, the area of the porous layer with decreased average pore diameter is the area with decreased pore diameter, the thickness of the area with decreased pore diameter is 35-55 μm, and the ratio of the thickness of the area with decreased pore diameter to the thickness of the area with increased pore diameter is 1.2-1.8.

It should be noted that the average pore diameter of the porous layer is firstly increased and then decreased from the area close to the protective layer side to the area close to the condensation layer side, the water vapor enters the porous layer from the protective layer, the water vapor circulates in the porous layer in a laminar flow manner, the circulation rate of the water vapor is gradually increased along with the increase of the pore diameter, the throughput of the water vapor is increased, the circulation rate of the water vapor is gradually reduced along with the decrease of the pore diameter, the water vapor enters the condensation layer at a proper flow rate, the phenomenon that the circulation rate of the water vapor is too high, the pore channels of the condensation layer are blocked, and the water conversion efficiency is reduced is avoided.

The aperture reducing area is of a proper length, so that the larger circulation rate of the water vapor is reduced between the aperture reducing areas so as to reduce the flow rate to a proper flow rate to avoid blocking of pore channels by the water vapor; meanwhile, the humidifying time of the hollow fiber membrane is increased, and the water conversion efficiency of the hollow fiber membrane is further reduced; if the ratio is smaller, the water vapor still has higher flow velocity when flowing into the condensation layer, so that the water vapor is easy to block the pore channels of the condensation layer, and the water conversion efficiency of the hollow fiber membrane is reduced.

Further, the distance between the position with the largest pore diameter in the porous layer and the inner surface is 65-80 μm, and accounts for 0.1-0.4 of the whole thickness of the membrane; the average pore diameter at the maximum pore diameter is 0.6-1.4 μm.

The porous layer has the maximum pore diameter, the average pore diameter is 0.6-1.4 microns, the circulation rate of water vapor is increased, the effect of gathering the water vapor is achieved, the phenomenon that the flow rate of the water vapor entering the condensation layer is too large and the pore channel of the condensation layer is blocked is avoided, the hollow fiber membrane has good water conversion efficiency, the passing time of the water vapor is prolonged, and the time cost is increased. The thickness of the position with the largest pore diameter accounts for 0.1-0.4 of the thickness of the whole membrane, so that the whole membrane has proper tensile strength, porosity and water vapor transmission rate. The distance between the position with the largest pore diameter in the porous layer and the inner surface is 65-80 mu m, if the distance is larger, the driving force of the water vapor is reduced, and the transmission rate of the water vapor is reduced; if the distance is smaller, the flow rate of the water vapor is larger, so that the water vapor is easy to gather to reduce the water conversion efficiency.

Further, the thickness of the hollow fiber membrane is 80-150 μm, the porosity is 50-80%, and the hollowness is 40-60%; the air permeability of the hollow fiber membrane is 0.02-0.7L/min/m ² @80KPa。

When the thickness of the hollow fiber membrane is small, the mechanical strength of the hollow fiber membrane is reduced, and the hollow fiber membrane is easily deformed by being pressed. When the thickness of the hollow fiber membrane is large, the time for water vapor to permeate the hollow fiber membrane is increased, resulting in excessive time cost. The thickness of the hollow fiber membrane provided by the application is 80-150 mu m, so that the hollow fiber membrane is ensured to have higher mechanical strength and higher water conversion efficiency, and the water vapor has higher permeation speed and lower time cost.

When the hollowness of the hollow fiber membrane is larger, the mechanical strength of the whole hollow fiber membrane is reduced, and the hollow fiber membrane is easy to deform under larger pressure, so that the humidifying effect of the hollow fiber membrane is influenced; when the hollowness of the hollow fiber membrane is smaller, the introduction amount of dry air in the inner cavity is reduced, and further the diffusion amount of water on the inner surface of the hollow inner fiber is reduced, so that water is gathered in the inner surface area of the hollow fiber membrane, and the humidifying effect of the hollow fiber membrane is reduced. The hollow fiber membrane provided by the application has proper hollowness, and sufficient mechanical strength is ensured, so that the hollow fiber membrane has the pressure-resistant and deformation-resistant effects; simultaneously, the air inlet quantity of the dry air is met, the water on the inner surface can be taken away in time, and the hollow fiber membrane has a good humidifying effect. The porosity of the hollow fiber membrane is 50% -80%, which is beneficial to increasing the water vapor transmission rate and the water conversion efficiency, and further increasing the humidifying effect of the membrane.

Flux, means the amount of substance that a hollow fiber membrane passes through per unit membrane area per unit time at a certain working pressure during separation. The flux of the air in the application is 10-25ml/min/m2@80KPa, and the flux is smaller, which indicates that the air permeation flux of the hollow fiber membrane is smaller; the hollow fiber membrane provided by the application has the water conversion efficiency of 40% -65%, ensures higher water conversion efficiency, simultaneously has smaller air throughput, and ensures that the hollow fiber membrane has good humidifying effect.

The method for producing a moisture-permeable asymmetric hollow fiber membrane as described in any one of the above,

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts 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 polyether sulfone;

the viscosity of the casting solution is 5000-30000cps;

the core liquid comprises a second organic solvent and a non-solvent, wherein the non-solvent is water and the content of the non-solvent is 50% -90%;

s2: spinning, namely extruding the casting solution and the core solution from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface;

s3: pre-phase separation, namely pre-phase separating the molded product through an air section, wherein the pre-phase separation time is 1-6s, the relative humidity of the air section is 20-40%, and the air flow rate is 0.3-0.6m/s;

s4: putting the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 20-50 ℃, the re-phase time is 15-55s, the coagulating bath is a mixture of water and a third organic solvent, and the water content in the coagulating bath is 60-100%;

s5: and stretching the raw membrane, cleaning the raw membrane in water, and finally drying to obtain the hollow fiber membrane.

Still further, 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 at least one of dimethyl sulfoxide, dimethylformamide, N-ethyl pyrrolidone, dimethylacetamide and N-methyl pyrrolidone;

in the method, a casting solution and a core solution are prepared, wherein the casting solution comprises a polysulfone polymer, a hydrophilic additive, a first organic solvent and sulfonated polyether sulfone, wherein the hydrophilic additive is at least one of polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine and polyvinyl alcohol, so that the hydrophilicity of the casting solution is increased, and the organic solvent is more easily dissolved by a coagulating bath under the combined action of the hydrophilic additive and the coagulating bath in a phase separation process, so that polysulfone is more easily precipitated, a polysulfone membrane with a proper pore diameter is formed, and the hydrophilicity of the prepared hollow fiber membrane is increased; the hydrophilicity of the membrane can be further increased by adding a small amount of sulfonated polyether sulfone into the membrane casting solution, and if the content of the sulfonated polyether sulfone is too high, the mechanical strength in the membrane forming process is lowered and becomes brittle, so that the tensile strength of the hollow fiber membrane is reduced. In addition, the viscosity of the membrane casting solution can be adjusted by adding sulfonated polyether sulfone, and the membrane casting solution has proper viscosity, so that the hollow fiber membrane is easier to form, and the inner surface and the outer surface have proper porosity. When the viscosity of the casting solution is higher, the diffusion speed of the non-solvent to the casting solution is lower, the phase separation speed is correspondingly lower, and the porosity of the inner surface and the outer surface is increased.

The core liquid comprises a second organic solvent and a higher-content non-solvent (water), the water content in the core liquid is 60% -100%, when the membrane casting liquid and the core liquid are extruded from the spinning nozzle at the same time, the temperature of the spinning nozzle is the same as that of the membrane casting liquid, the temperature of the membrane casting liquid is prevented from being influenced by the overhigh temperature of the spinning nozzle, and along with the increase of the content of the non-solvent in the core liquid, the lower the porosity of the inner surface of the hollow fiber membrane is, the smoother the inner surface is. In addition, as the sulfonated polyether sulfone is a water-soluble substance, according to a similar compatibility principle, the sulfonated polyether sulfone gradually moves to the core liquid, so that the content of the sulfonic acid groups on the inner surface is greater than that on the outer surface, and the content of the sulfonic acid groups gradually decreases from the inner surface to the outer surface, so that the hydrophilicity gradually decreases from the inner surface to the outer surface. The formed product with inner and outer surfaces is placed in air flow with proper humidity, the phase separation speed is high, and is favorable for forming proper hole structure near the outer surface area and the outer surface, so that a layer of small hole structure is formed along the film thickness direction, the formed product with pre-phase separation is placed in a coagulating bath for phase separation, the coagulating bath permeates from the inner and outer surfaces to the inner surface along the film thickness direction, and the phase separation is carried out, thus ensuring that the first organic solvent is fully separated out. When the water content in the coagulating bath is less, the coagulating bath permeates into the hollow fiber membrane along the pore channel formed on the outer surface of the pre-phase separation phase, the phase separation speed is slow, a macroporous structure is formed firstly, then the macroporous structure is gradually diffused to the inner surface, and the formed pore diameter is gradually reduced along with the reduction of the diffusion speed and is in gradient distribution; the coagulating bath permeates into the hollow fiber membrane along the pore channel formed on the outer surface in the pre-divided phase; when the water content in the coagulating bath is relatively high, the phase splitting speed is high, pores with small pore diameters are formed firstly, the pores are formed to be gradually increased along with the increase of the infiltration amount of the coagulating bath, the coagulating bath infiltrates into the film with a certain thickness, the infiltration speed is gradually reduced, and the formed pore diameters are gradually reduced. The formed raw film is stretched by 1-5 times at a stretching rate of 3-12m/min, so that the shrinkage of holes formed by phase splitting can be effectively avoided, the sizing effect is achieved, the pore size of the same level is uniform at a proper stretching rate, and the poor stretching effect caused by fiber breakage or small stretching multiple due to too large stretching efficiency multiple can be effectively avoided by a proper stretching multiple. And finally, cleaning in water, and drying after cleaning to obtain the hollow fiber membrane.

The following beneficial effects can be brought through the application: the hollow fiber membranes provided herein exhibit better water conversion efficiency, lower gas throughput, and better tensile strength. Greatly improves the performance of the hollow fiber membrane taking the polysulfone polymer as the main material and prolongs the service life of the hollow fiber membrane. The preparation method provided by the invention can conveniently, quickly and effectively prepare the hollow fiber membrane.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:

FIG. 1 is a Scanning Electron Microscope (SEM) image of the near-inner surface of a hollow fiber membrane prepared in example 2, at a magnification of 5000 ×;

FIG. 2 is a Scanning Electron Microscope (SEM) image of the near outer surface of a hollow fiber membrane prepared in example 2, wherein the magnification is 2000 ×;

FIG. 3 is a Scanning Electron Microscope (SEM) image of the inner surface of the hollow fiber membrane obtained by preparation of example 2, wherein the magnification is 5000 ×;

FIG. 4 is a Scanning Electron Microscope (SEM) image of the outer surface of a hollow fiber membrane prepared in example 2, wherein the magnification is 5000 ×;

FIG. 5 is a Scanning Electron Microscope (SEM) image of a cross-section of a hollow fiber membrane prepared in example 7, wherein the magnification is 1000 ×;

FIG. 6 is a Scanning Electron Microscope (SEM) image of the near inner surface of a hollow fiber membrane prepared in example 7 at a magnification of 10000;

FIG. 7 is a Scanning Electron Microscope (SEM) image of the near-outer surface of a hollow-fiber membrane prepared in example 7, at a magnification of 10000 ×;

FIG. 8 is a Scanning Electron Microscope (SEM) image of the inner surface of the hollow-fiber membrane obtained by preparation of example 7, wherein the magnification is 10000 ×;

FIG. 9 is a Scanning Electron Microscope (SEM) image of the outer surface of a hollow fiber membrane prepared in example 7, at a magnification of 10000;

reference numerals are as follows: a. a protective layer; b. a porous layer; c. and (4) a condensation layer.

Detailed Description

In order to more clearly explain the overall concept of the present application, the following detailed description is given by way of example. In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present application. It will be apparent, however, to one skilled in the art, that the present application may be practiced without one or more of these specific details. In other instances, well-known features of the art have not been described in order to avoid obscuring the present application.

In the following examples, raw materials and equipment for preparing hollow fiber membranes were commercially available, unless otherwise specified. Wherein the structural morphology of the filter membrane is characterized by adopting a scanning electron microscope with the model number of S-5500 provided by Hitachi company.

Example 1

S1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 20 parts of polyether sulfone, 15 parts of polyethylene glycol, 55 parts of dimethyl sulfoxide and 2.5 parts of sulfonated polyether sulfone;

the viscosity of the casting solution is 10000cps;

the core liquid comprises dimethylformamide and a non-solvent, wherein the non-solvent is water and the content of the non-solvent is 85%;

the polysulfone polymer is at least one of polyether sulfone, polysulfone and polyarylsulfone.

s3: pre-phase separation, namely pre-phase separating the molded product through an air section, wherein the pre-phase separation time is 3s, the relative humidity of the air section is 30%, and the air flow rate is 0.35m/s;

s4: placing the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 38 ℃, the re-phase separation time is 30s, the coagulating bath is a mixture of water and dimethylacetamide, and the water content in the coagulating bath is 85%;

s5: and (3) stretching the green membrane at a stretching speed of 8m/min by 2.5 times, washing in water, and finally drying to obtain the hollow fiber membrane.

Example 2

S1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 18 parts of polysulfone, 10 parts of polyvinylpyrrolidone, 60 parts of N-ethyl pyrrolidone and 2 parts of sulfonated polyether sulfone;

the viscosity of the casting solution is 15000cps;

the core liquid comprises dimethylacetamide and a non-solvent, wherein the non-solvent is water, and the content of the non-solvent is 55%;

s3: pre-phase separation, namely pre-phase separating the molded product through an air section, wherein the pre-phase separation time is 4s, the relative humidity of the air section is 20%, and the air flow rate is 0.5m/s;

s4: putting the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 29 ℃, the re-phase separation time is 35s, the coagulating bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulating bath is 70%;

s5: and (3) stretching the green membrane at a stretching speed of 4m/min, washing the green membrane in water, and drying to obtain the hollow fiber membrane.

Example 3

S1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 19 parts of polyarylsulfone, 8 parts of polyvinyl alcohol, 65 parts of N-methylpyrrolidone and 3 parts of sulfonated polyether sulfone;

the viscosity of the casting solution is 7000cps;

the core liquid comprises dimethyl sulfoxide and a non-solvent, wherein the non-solvent is water, and the content of the non-solvent is 75%;

s3: pre-phase separation, namely pre-phase separating the molded product through an air section, wherein the pre-phase separation time is 2s, the relative humidity of the air section is 25%, and the air flow rate is 0.4m/s;

s4: placing the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 25 ℃, the re-phase separation time is 20s, the coagulating bath is a mixture of water and dimethylformamide, and the water content in the coagulating bath is 90%;

s5: and (3) stretching the green membrane at a stretching speed of 9m/min by 2 times, washing in water, and finally drying to obtain the hollow fiber membrane.

Example 4

S1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 21 parts of polysulfone, 17 parts of polyethyleneimine, 70 parts of N-ethyl pyrrolidone and 3.5 parts of sulfonated polyether sulfone;

the viscosity of the casting solution is 20000cps;

the core liquid comprises N-methyl pyrrolidone and a non-solvent, wherein the non-solvent is water, and the content of the non-solvent is 60%;

s3: pre-phase separation, namely pre-phase separating the molded product through an air section, wherein the pre-phase separation time is 1.5s, the relative humidity of the air section is 35%, and the air flow rate is 0.45m/s;

s4: placing the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 30 ℃, the re-phase separation time is 25s, the coagulating bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulating bath is 65%;

s5: and (3) stretching the green membrane, wherein the stretching speed is 10m/min, stretching the green membrane by 4 times, cleaning the green membrane in water, and finally drying to obtain the hollow fiber membrane.

Example 5

S1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 22 parts of polyarylsulfone, 12 parts of polyethylene glycol, 75 parts of N-ethyl pyrrolidone and 1.5 parts of sulfonated polyether sulfone;

the viscosity of the casting solution is 8000cps;

the core liquid comprises dimethyl sulfoxide and a non-solvent, wherein the non-solvent is water and the content of the non-solvent is 65%;

s3: pre-phase separation, namely pre-phase separation is carried out on the molded product through an air section, the time of the pre-phase separation is 3.5s, the relative humidity of the air section is 40%, and the air flow rate is 0.55m/s;

s4: placing the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 35 ℃, the re-phase separation time is 50s, the coagulating bath is a mixture of water and dimethylacetamide, and the water content in the coagulating bath is 80%;

s5: and (3) stretching the green membrane at a stretching speed of 11m/min by 3.5 times, washing in water, and finally drying to obtain the hollow fiber membrane.

Example 6

S1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 23 parts of polysulfone, 19 parts of polyvinylpyrrolidone, 80 parts of dimethylacetamide and 4 parts of sulfonated polyether sulfone;

the viscosity of the casting solution is 12000cps;

the core liquid comprises N-methyl pyrrolidone and a non-solvent, wherein the non-solvent is water and the content of the non-solvent is 70%;

s3: pre-phase separation, namely passing the molded product through an air section for pre-phase separation, wherein the pre-phase separation time is 5s, the relative humidity of the air section is 28%, and the air flow rate is 0.6m/s;

s4: placing the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 40 ℃, the re-phase separation time is 40s, the coagulating bath is a mixture of water and dimethyl sulfoxide, and the water content in the coagulating bath is 75%;

s5: and (3) stretching the green membrane at a stretching speed of 6m/min by 1.5 times, washing in water, and finally drying to obtain the hollow fiber membrane.

Example 7

S1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 24 parts of polyether sulfone, 7 parts of polyvinyl alcohol, 67 parts of dimethylacetamide and 4.5 parts of sulfonated polyether sulfone;

the viscosity of the casting solution is 9000cps;

the core liquid comprises N-ethyl pyrrolidone and a non-solvent, wherein the non-solvent is water and the content of the non-solvent is 80%;

s3: pre-phase separation, namely pre-phase separating the molded product through an air section, wherein the pre-phase separation time is 4.5s, the relative humidity of the air section is 32%, and the air flow rate is 0.3m/s;

s4: placing the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 45 ℃, the re-phase separation time is 45s, the coagulating bath is a mixture of water and a third organic solvent, and the water content in the coagulating bath is 95%;

s5: and (3) stretching the green membrane at a stretching speed of 7m/min by 2.5 times, washing in water, and finally drying to obtain the hollow fiber membrane.

Example 8

S1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 17 parts of polysulfone polymer, 14 parts of polyethyleneimine, 74 parts of dimethylacetamide and 1 part of sulfonated polyether sulfone;

the viscosity of the casting solution is 21000cps;

the core liquid comprises a second organic solvent and a non-solvent, wherein the non-solvent is water and the content of the non-solvent is 90%;

s3: pre-phase separation, namely pre-phase separating the molded product through an air section, wherein the pre-phase separation time is 5.5s, the relative humidity of the air section is 38%, and the air flow rate is 0.4m/s;

s4: placing the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 43 ℃, the re-phase separation time is 55s, the coagulating bath is a mixture of water and dimethylformamide, and the water content in the coagulating bath is 60%;

s5: and (3) stretching the green membrane at a stretching speed of 5m/min by 4.5 times, washing in water, and finally drying to obtain the hollow fiber membrane.

Comparative example 1

S1, preparing a casting solution and a core solution;

the viscosity of the casting solution is 10000cps;

the bore fluid comprises dimethylformamide and a non-solvent, wherein the non-solvent is water, and the content of the non-solvent is 20%;

s3: pre-phase separation, namely pre-phase separating the molded product through an air section, wherein the pre-phase separation time is 3s, the relative humidity of the air section is 10%, and the air flow rate is 0.35m/s;

Comparative example 1 and example 1 under the same conditions of other step parameters, reduce the content of non-solvent in bore fluid, make the inner surface of hollow fiber membrane have pore structure, reduce the tensile strength and water conversion efficiency of hollow fiber membrane, increase the gas throughput.

Comparative example 2

S1, preparing a casting solution and a core solution;

the viscosity of the casting solution is 40000cps;

s3: pre-phase separation, namely, pre-phase separation is carried out on the molded product through an air section, the time of the pre-phase separation is 3s, the relative humidity of the air section is 30%, and the air flow rate is 0.35m/s;

s4: placing the pre-phase-separated molded product into a coagulating bath for re-phase separation to form a raw film, wherein the temperature of the coagulating bath is 38 ℃, the re-phase separation time is 30s, the coagulating bath is a mixture of water and dimethylacetamide, and the water content in the coagulating bath is 30%;

Comparative example 2 under the same conditions as other process parameters of example 1, the viscosity of the dope solution was increased to form a dense surface on the inner surface, and the water conversion efficiency of the hollow fiber membrane was decreased (high tensile strength).

Performance test

Structural characterization

The hollow fiber membranes obtained in each example and comparative example were subjected to respective morphological characterization of longitudinal section, inner surface and outer surface, measurement of thickness and average pore diameter of each layer in the hollow fiber membrane, and measurement of average fiber diameter, porosity and degree of hollowness of the hollow fiber membrane, wherein the measurement data are shown in tables 1 to 4, and the morphological characterization results of examples 1 to 8 are shown in fig. 1 to 9, wherein a is a protective layer, b is a porous layer, and c is a condensation layer.

The hollow fiber membranes obtained in the examples were subjected to contact angle measurement of the inner and outer surfaces using a contact angle measuring instrument.

The roughness of the inner surface and the outer surface of the hollow fiber membrane obtained in each example is tested by a roughness tester.

TABLE 1 structural characterization of hollow fiber membranes

TABLE 2 structural characterization of hollow fiber membranes

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TABLE 3 structural characterization of hollow fiber membranes

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TABLE 4 structural characterization of hollow fiber membranes

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1. Performance test

The hollow fiber membranes obtained in each example were tested for tensile strength and elongation using a tensile tester.

The hollow fiber membranes obtained in each example were tested for water conversion efficiency.

The hollow fiber module is manufactured by self, wet air enters from wet in end, and dry air enters from dry in end. And (5) respectively monitoring the dry out end and the wet out end by using a digital display hygrothermograph, and observing the humidifying effect. Different humidification data are obtained by changing the gas flow sizes of the dry in end and the wet in end. Different humidification data are obtained by adding a one-way pressure relief valve at the outlet of the dry out end to increase the dry flow pressure.

And (3) calculating the result:

in the formula: d-density of dry gas or moisture in g/m ³ )，K ₁ 、K ₂ Constant, T-temperature of hollow fiber membrane dry in end, dry out end, wet in end or wet out end in DEG C, T ₁ Temperature constant, in units (. Degree. C.),

-the humidity of the hollow fiber membrane dry in end, dry out end, wet in end or wet out end in (% RH).

V＝Q*H

In the formula: v-volume of dry or wet gas in units of (m) ³ ) Q-the volume flow of dry or wet gas, in units of (m) ³ H), H-gas flow time in units of H.

m＝ρ*v

Wherein the unit of the water content of the m-hollow fiber membrane dry out end or the hollow fiber membrane wet in end is (g), and the unit of rho is the density of dry gas or wet gas ³ ) V-volume of dry or wet gas,unit (m) ³ )。

In the formula: omega-water conversion efficiency, m ₁ Water content in (g), m at the dry out end of the hollow fiber membrane ₂ The water content at the wet in end of the hollow fiber membrane is given in (g).

The hollow fiber membranes obtained in each example were subjected to air permeability measurement by a gas flow meter.

Table 5 hollow fiber membrane performance testing of each example

The above description is only an example of the present application and is not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A moisture permeable asymmetric hollow fiber membrane comprises a main body, wherein a non-directional tortuous passage is formed in the main body, one side surface of the main body is an outer surface, and the other side surface of the main body is an inner surface;

the protective layer side is the outer surface, the condensation layer side is the inner surface, the average pore size of the porous layer is larger than the average pore size of the protective layer, and the average pore size of the protective layer is larger than the average pore size of the condensation layer;

the average pore diameter of the outer surface is 80-250nm; the average pore diameter of the inner surface is 10-60nm; the water conversion efficiency of the hollow fiber membrane is 45-65%.

2. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the void area ratio of the outer surface is 8% to 15%, and the void area ratio of the inner surface is 0.5% to 5%; the ratio of the average pore diameter of the outer surface to the average pore diameter of the inner surface is 2-8.

3. The moisture permeable asymmetric hollow fiber membrane according to claim 1, wherein the roughness of the outer surface is 10-30 μ ι η; the roughness of the inner surface is 5-20 μm; and the roughness of the outer surface is greater than the roughness of the inner surface.

4. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the average pore diameter of the protective layer is 150 to 350nm, the thickness of the protective layer is 3 to 10 μm, and the thickness of the protective layer is 3 to 10% of the thickness of the hollow fiber.

5. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the porosity of the protective layer is 30 to 60%, and the fibers forming a porous structure in the protective layer are first fibers in the form of a strip, and the average diameter of the first fibers is 80 to 150nm.

6. The moisture permeable asymmetric hollow fiber membrane of claim 1, wherein the first water contact angle of the outer surface is 65-87 °, and the difference between the first water contact angle of the outer surface and the first water contact angle of the inner surface is 10-35 °.

7. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the average pore diameter of the porous layer is 250 to 650nm; the thickness of the porous layer is 65-120 μm, and the thickness of the porous layer accounts for 65% -80% of the thickness of the hollow fiber membrane; the thickness of the porous layer is 60-110 μm greater than that of the protective layer.

8. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein an average pore diameter of the porous layer is 1.4 to 2.5 times an average pore diameter of the protective layer; the porosity of the porous layer is 55-85%, the fibers forming the porous structure in the porous layer are strip-shaped second fibers, and the average diameter of the second fibers is 130-180nm; the ratio of the average diameter of the second fibers to the average diameter of the first fibers is 1.2 to 1.8.

9. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the thickness of the condensation layer is 5 to 20 μm, and the thickness of the condensation layer accounts for 8 to 15% of the thickness of the hollow fiber membrane.

10. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the average pore diameter of the region of the condensation layer on the porous layer side decreases in a gradient manner toward the region on the inner surface side, the average pore diameter of the condensation layer is 40 to 140nm, and the porosity of the condensation layer is 15 to 50%.

11. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the condensation layer has a skin region, one side of the skin region is an inner surface, and the thickness of the skin region accounts for 2% -10% of the thickness of the condensation layer; the skin region has a porosity of no greater than 10%.

12. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the average pore diameter of the porous layer decreases in a gradient from a region on the side close to the protective layer to a region on the side close to the condensation layer, and the average pore diameter of the porous layer varies in a gradient of 4 to 8nm/um.

13. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the average pore diameter of the porous layer increases and then decreases from a region on the side close to the protective layer to a region on the side close to the condensation layer;

the area of the porous layer with increased average pore diameter is the area with increased pore diameter, the area of the porous layer with decreased average pore diameter is the area with decreased pore diameter, the thickness of the area with decreased pore diameter is 35-55 μm, and the ratio of the thickness of the area with decreased pore diameter to the thickness of the area with increased pore diameter is 1.2-1.8.

14. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the distance between the maximum pore diameter position in the porous layer and the inner surface is 65-80 μm, and accounts for 0.4-0.8 of the overall thickness of the membrane; the average pore diameter at the maximum pore diameter is 0.6-1.4 μm.

15. The moisture-permeable asymmetric hollow fiber membrane according to claim 1, wherein the thickness of the hollow fiber membrane is 80 to 150 μm, the porosity is 50 to 80%, and the hollowness is 40 to 60%; the air permeability of the hollow fiber membrane is 0.02-0.7L/min/m ² @80KPa。

16. The method for producing a moisture-permeable asymmetric hollow fiber membrane according to any one of claims 1 to 15, characterized in that:

s1, preparing a casting solution and a core solution;

the viscosity of the casting solution is 5000-30000cps;

17. The method of claim 16, wherein the hydrophilic additive is at least one of polyethylene glycol, polyvinylpyrrolidone, polyethyleneimine, and polyvinyl alcohol;