CN115888422A - Hollow fiber membrane with high moisture permeability and low air permeability as well as preparation method and application thereof - Google Patents

Abstract

The invention relates to the technical field of moisture permeable membrane materials, and provides a hollow fiber membrane with high moisture permeability and low air permeability, and a preparation method and application thereof. The hollow fiber membrane with high moisture permeability and low air permeability comprises a main body, wherein one side of the main body is an inner surface, the other side of the main body is an outer surface, a non-directional tortuous passage is arranged in the main body, and the average pore diameter of the main body is in gradient change from an area close to the outer surface to an area close to the inner surface. The main part includes capillary condensation layer and supporting layer, and one side of capillary condensation layer is the internal surface, and one side of supporting layer is the surface. The other side of the capillary condensation layer and the other side of the support layer are in transition with continuous fibers. The average pore diameter of the outer surface is 200-650nm. The inner surface is a dense surface. The polysulfone hollow fiber membrane structure provided by the application shows higher water conversion efficiency, low gas throughput and better tensile strength, and can run for a long time at high temperature and high pressure.

Description

Hollow fiber membrane with high moisture permeability and low air permeability as well as preparation method and application thereof

Technical Field

The invention relates to the technical field of moisture permeable membrane materials, in particular to a hollow fiber membrane with high moisture permeability and low air permeability, a preparation method and application thereof.

Background

The polysulfone polymer is an excellent membrane material, and the prepared hollow fiber membrane has high pressure resistance, heat resistance and oxidation resistance, has better biocompatibility than other membrane materials, and has certain hydrophilicity. Among them, the polysulfone polymer microporous membrane is widely used in the fields of industry, medicine or medicine.

The hollow fiber membrane is in a fiber shape and is an asymmetric membrane with a self-supporting function, and the dense layer is positioned on the outer surface or the inner surface of the fiber. Hollow fiber membranes are an important form of separation membranes, hollow fiber ultrafiltration membranes, hollow fiber microfiltration membranes, hollow fiber reverse osmosis membranes, hollow fiber gas separation membranes, and the like. The method is mainly applied to the fields of water purification, medicine purification, humidification treatment and the like.

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.

Patent CN102481524B, published by eastern japan ltd 2014, provides a water vapor permeable membrane, a hollow fiber membrane prepared therefrom, and a hollow fiber membrane module suitable for use in a fuel cell system. With an asymmetric morphology, one side of the membrane has a dense layer and the other side of the membrane has finger-shaped holes. Although such a structure ensures the permeability of water vapor, the area of the hollow portion in the finger-shaped hole is large, resulting in low tensile strength and failure to withstand large pressure.

At present, how to prepare a hollow fiber membrane with higher tensile strength and excellent moisture permeability is a problem to be solved urgently by technical personnel in the field.

Disclosure of Invention

In order to solve the above problems, the present invention aims to provide a hollow fiber membrane with high moisture permeability and low air permeability, and a method for preparing the hollow fiber membrane, wherein the hollow fiber membrane can show high water conversion efficiency, high tensile strength and low gas throughput, greatly improve the performance of the hollow fiber membrane using polysulfone polymers as main materials, and prolong the service life of the hollow fiber membrane.

In one aspect, a hollow fiber membrane with high moisture permeability and low air permeability comprises a main body, wherein one side of the main body is an inner surface, the other side of the main body is an outer surface, and a non-directional tortuous passage is formed in the main body, wherein the average pore diameter of the main body is in gradient change from a region close to the outer surface to a region close to the inner surface; the main body comprises a capillary condensation layer and a supporting layer, wherein 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 support layer are transited by continuous fibers; the average pore diameter of the outer surface is 200-650nm; the inner surface is a dense surface.

When the dense surface is shot by a scanning electron microscope at 50000 times, the pore area ratio (namely the pore area: the internal surface area) of the internal surface is not more than 6%, namely, two conditions of an unobservable pore structure or an observable few pore structures exist, and the pore diameter of the observable pore structure is not more than 50nm, more preferably not more than 20nm, and even more preferably not more than 10nm. The capillary condensation layer is a region where water vapor is converted from vapor to liquid. The support layer is a region where water vapor permeates into the hollow fiber membrane and diffuses in the form of vapor. By "continuous fiber transition" is understood that the fibers between the capillary condensation layer and the support layer are "integrally formed" and are present as an integral continuous connection without additional adhesive bonding, and the continuous fibers cannot be separated from each other unless torn by an external force. The measurement mode of the average pore diameter of the membrane surface can be realized by performing morphology characterization on a membrane structure by using a scanning electron microscope, then performing measurement by using computer software (such as Matlab, NIS-Elements and the like) or manually, and performing corresponding calculation; in the preparation process of the membrane, in the direction perpendicular to the thickness of the membrane (if the membrane is in the form of a flat plate membrane, the direction is a planar direction; if the membrane is in the form of a hollow fiber membrane, the direction is perpendicular to the radial direction), the characteristics such as the pore size distribution are substantially uniform and substantially uniform; 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 times 5 μm), the specific area size is determined according to the actual situation,measuring the pore diameters of all the pores in the area by corresponding computer software or manually, and then calculating 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. In the application, the capillary condensation layer and the supporting layer are both made of the same material, the two layers are combined into an integral structure and are directly formed in the membrane preparation process, and only one change is made in the membrane structure in the transition from the capillary condensation layer to the supporting layer, so that the membrane prepared by the application is an asymmetric membrane; in contrast, for example, composite membranes, which have a multilayer structure and in which a dense layer as the separating layer is applied in a separate process step to a porous, frequently microporous, support layer or support membrane, the materials of which the support layer and the separating layer are composed often also being different.

In the hollow fiber membrane provided by the application, a sponge-like network structure is formed by the non-directional tortuous path of the fibers between the inner surface and the outer surface of the main body. The average pore diameter of the main body changes in a gradient from the area close to the outer surface side to the area close to the inner surface side, and further, the gradient is gradually reduced. Where "tapering" is understood to mean monotonically decreasing, i.e. any two mean pore diameters being independent of variable X ₁ And X ₂ When X is present ₂ ＜X ₁ When, there is f (X) ₂ )＜f(X ₁ ) And the average pore diameter is continuously decreased, namely, a state of fluctuation which is increased, decreased or decreased and stabilized does not exist. The average pore diameter of membrane reduces to being close to the internal surface region by being close to the surface region gradually in this application, and finger-like hole among this kind of structure and the prior art compares, and the membrane is inside to form the hole of non-directional tortuous by the fibre of labyrinth complicated, has avoided local hollow part area too big, and the tensile strength that leads to the membrane is low, has guaranteed that the hollow fiber membrane of this application preparation has great tensile strength. In addition, it should be noted that the gradient change of the membrane pore diameter reflects the change of the overall pore diameter on the cross section of the membrane main body, and does not include the moisture permeable pores which are haphazardly appeared on the cross section and are extremely small in number, and the pore diameter of the moisture permeable pores is larger than that of the nearby pores.

The main body can be divided into a supporting layer and a capillary condensation layer according to the size of the area pore diameter, and the average pore diameter of the capillary condensation layer is smaller than that of the supporting layer. Water vapor enters the hollow fiber membranes from the pores of the outer surface of the support layer. According to the capillary condensation theory, in the permeation process of water vapor, as the pore diameter of the membrane is gradually reduced, the water vapor can be condensed into liquid water, namely, the liquid water enters the capillary condensation layer, at the moment, the concentration of the water in the area of the hollow fiber membrane close to the inner surface is greater than that of the water on the inner surface, a concentration difference is formed, and the water is diffused from high concentration to low concentration, namely, the water is diffused to the inner surface from the area close to the inner surface. 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 effect is further realized. On one hand, when the steam is condensed into water in the capillary condensation layer, the water blocks a flow passage close to the inner surface area, so that other gases can be effectively prevented from passing through, and further the throughput of the gases is reduced. On the other hand, the pore diameter of the pores on the compact surface formed by the method is extremely small, the gas throughput is further reduced, and meanwhile, the low pore area rate of the compact surface enables the compact surface to have high mechanical strength, so that the compact surface plays a role in supporting the whole hollow fiber membrane, the whole membrane has good mechanical strength, the compact surface is not easy to damage under high pressure, and the service life of the compact surface is prolonged.

Wherein, the average pore diameter of the outer surface is 200-650nm, when the average pore diameter of the outer surface is too large, the mechanical strength is reduced, when the membrane is subjected to too large pressure, the holes close to the outer surface area are easy to collapse, 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 method has a proper average pore diameter, so that the throughput of water vapor is ensured, the throughput of gas is reduced, the mechanical strength of the outer surface is also met, and the membrane has good tensile strength.

In conclusion, the hollow fiber membrane provided by the application has better tensile strength, lower gas throughput and better water vapor throughput, and the humidifying effect of the membrane is improved.

Further, the average pore diameter variation gradient of the hollow fiber membrane is 2-8 nm/mum, and the porosity of the hollow fiber membrane is 60% -85%.

It should be noted that the average pore diameter variation gradient of the hollow fiber membrane of the present application is calculated according to the formula:

wherein the content of the first and second substances,

-a gradient of variation of the mean pore diameter in units of (nm/μm); />

-the average pore size of the outer surface in (nm); />

-the average pore size of the inner surface in (nm); t-hollow fiber membrane thickness, in μm.

In the application, the average pore diameter in the thickness direction of the membrane is in gradient change within the range of 2-8 nm/mum, preferably, the average pore diameter change gradient is 3-7 nm/mum, and the proper average pore diameter gradient change range ensures that the hollow parts formed by the holes in the hollow fiber membrane are more uniformly distributed in the gradient change, so that the hollow fiber membrane has higher tensile strength as a whole. Meanwhile, the average pore diameter of the hollow fiber membrane is changed in a gradient manner within a proper range, so that the hollow fiber membrane has high porosity which is 60-85%, the increase of water conversion efficiency is facilitated, and the humidifying effect of the membrane is further increased.

Still further, the first water contact angle of the inner surface is 8-35 ° less than the first water contact angle of the outer surface; preferably, 12-32 ° smaller; more preferably, 15-28 °; and the first water contact angle from the inner surface to the outer surface in the thickness direction of the film is in gradient change.

It should be noted that the hollow fiber membrane may be torn first, divided into several layers, and then tested for corresponding parameters by using a contact angle tester, or those skilled in the art may obtain the above parameters by using other measuring means, which are only used for reference.

In the present application, the first water contact angle in the thickness direction of the film from the inner surface to the outer surface increases in a gradient manner, and since the water contact angle of the film surface is related to the hydrophilicity of the film surface (i.e., the greater the first water contact angle, the poorer the hydrophilicity; and the smaller the first water contact angle, the better the hydrophilicity), the hydrophilicity in the thickness direction of the film from the inner surface to the outer surface decreases in a gradient manner. The change in hydrophilicity is also one of the driving forces for water movement, and water moves from a place with weak hydrophilicity to a place with strong hydrophilicity, that is, water in the hollow fiber membrane flows toward the inner surface with good hydrophilicity under the change of the hydrophilicity gradient. When the first contact angles of the inner surface and the outer surface are different greatly, the water contact angle of the inner surface is too small, water is easy to store on the inner surface and is not easy to diffuse outwards, and the humidifying effect of the hollow fiber membrane is reduced. When the difference between the first contact angles of the inner surface and the outer surface is smaller, the driving force for moving water in the flow channel is reduced, so that the water conversion efficiency is reduced, and the humidifying effect of the hollow fiber membrane is further reduced. A large number of tests show that the water contact angle of the inner surface of the hollow fiber membrane is 8-35 degrees smaller than that of the outer surface of the hollow fiber membrane, so that water in the hollow fiber membrane flows to the inner surface and is easy to diffuse outwards, and the humidifying effect of the hollow fiber membrane is improved.

Still 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 °.

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 concentrated in the area close to the inner surface of 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 the outer surface water contact angle is less, the hydrophilicity near the outer surface area is great, is unfavorable for the diffusion of water vapor to the inner surface, and then reduces the throughput of water vapor, and the outer surface of this application has suitable first water contact angle, has increased the volume that water vapor got into the outer surface, effectively avoids water vapor to gather in outer surface area simultaneously, helps improving hollow fiber membrane's water conversion efficiency.

Still further, the roughness of the inner surface is less than the roughness of the outer surface.

It should be noted that, when the surface of the membrane has a relatively large roughness, the solid surface has a relatively low free energy, so that the membrane has a relatively large first water contact angle and thus relatively poor hydrophilicity. When the roughness of the surface of the film is lower, the free energy of the solid surface of the film is higher and lower, so that the film has a smaller first water contact angle and further has better hydrophilicity. The outer surface has relatively large roughness, and when gas passes through the outer surface, the gas is easy to be adsorbed on the outer surface with large roughness, so that the gas passing through is reduced; the roughness of internal surface is less than the roughness of surface in this application, and the hydrophilicity of internal surface is better than the hydrophilicity of surface promptly, has provided the drive power to the internal surface flow for the inside water of hollow fiber membrane, and when the internal surface is more smooth, when gas blows through the internal surface, energy loss is less, and then has less pressure drop. 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. Carry out the roughness test through the roughness tester to hollow fiber membrane in this application, survey interior external surface and have suitable roughness for interior, surface all have suitable hydrophilicity, help permeating through of steam.

Still further, the thickness of the capillary condensation layer is 8-25 μm, and accounts for 8% -20% of the thickness of the hollow fiber membrane main body.

It should be noted that the thickness of the capillary condensation layer as a percentage of the thickness of the hollow fiber membrane body in the present application determines the water conversion efficiency and gas throughput. When the percentage of the water vapor is larger, the capillary condensation layer is thicker, so that the diffusion speed of water condensed by the water vapor in the hollow fiber membrane is reduced, and the throughput of the water vapor is reduced. When the percentage of the water vapor is too small, the capillary condensation layer is thin, 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, and the throughput of the gas is increased. 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 are beneficial to improving the conversion efficiency of water and effectively avoiding the permeation of gas.

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

Still further, the thickness of the support layer is 65-100 μm, the average pore diameter of the support layer is 150-550nm, and the average porosity of the support layer is 65-90%.

It should be noted that, in general, water vapor exists in the support layer in a vapor form, and the thickness, the average pore size and the average porosity of the support layer have a certain influence on the permeation rate and the throughput of the water vapor. When the average porosity of the support layer is too large, the throughput of water vapor is increased, and when the average pore diameter of the support layer is larger, 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 pores are present inside the film, resulting in a decrease in the tensile strength of the film. When the average pore diameter of the support layer is too large, the hollow structure inside the membrane is made too large, resulting in a decrease in the tensile strength of the membrane. The support layer in the present application has a suitable thickness, average pore size and porosity, so that the water vapor has a high permeation rate and a large throughput, while ensuring the tensile strength of the hollow fiber membrane.

Still further, the average pore diameter of the capillary condensation layer is 20-120nm, and the porosity of the capillary condensation layer is 15% -50%.

It should be noted that, when the average pore diameter of the capillary condensation layer is larger, the diffusion rate of water in the flow channel is accelerated, the effect of blocking gas permeation is reduced, and the gas throughput is increased. When the average pore diameter of the capillary condensation layer is smaller, gas permeation is effectively avoided, and the diffusion rate of water is reduced. Therefore, the average pore diameter of the capillary condensation layer is 20-120nm, so that the water has a better diffusion rate, and the gas throughput is effectively reduced. When the porosity of the capillary condensation layer is too large, the tensile strength of the film is reduced although the water throughput is increased. When the porosity of the capillary condensation layer is too small, the tensile strength of the membrane is increased, but the water passage is decreased. Therefore, the porosity of the capillary condensation layer is 15% -50%, and the tensile strength of the membrane is guaranteed while the water flux is guaranteed.

Still further, the capillary condensation layer comprises a skin region, and one side of the skin region is an inner surface; the thickness of the skin zone area accounts for 15% -25% of the thickness of the capillary condensation layer, and the porosity of the skin zone area does not exceed 10%.

It should be noted that, the skin region is shot by a scanning electron microscope at 50000 times, and the porosity of the skin region is not more than 10%, that is, there are two cases that the porosity of the hole structure which can not be observed and the porosity of the hole which can be observed are not more than 10%.

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 skin region is thinner, although the water vapor transmission rate is increased, the tensile strength of the film as a whole is reduced. Therefore, the thickness of the skin layer area accounts for 15% -25% of the thickness of the capillary 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 body comprises fibers forming a porous structure, and the fibers are in a strip-shaped structure; the average diameter of the fibers is 200-500nm.

The average diameter of the fiber in the present application can be obtained by using a scanning electron microscope to perform morphology characterization on the cross-sectional structure of the hollow fiber membrane, then using computer software (such as Matlab, NIS-Elements, etc.) or manually performing measurement, and then calculating the average value, and those skilled in the art can also obtain the above parameters by other measurement means.

In the application, the main body is of a porous structure formed by strip-shaped fibers, wherein the fibers are uniformly distributed, the average diameter of the fibers is 200-500nm, and when the average diameter of the fibers is larger, the overall porosity is reduced, so that the water conversion efficiency is influenced; when the average diameter of the fiber is small, the hollow area ratio of the hollow fiber membrane is increased, and further the mechanical strength of the hollow fiber membrane is reduced, and when the hollow fiber membrane is subjected to large pressure, the hollow fiber membrane is easy to deform.

The average diameter of the fibers of the hollow fiber membrane provided by the application is 200-500nm, and the hollow fiber membrane can play a certain supporting and protecting role on the supporting layer, so that the hole structure formed by the hollow fiber membrane is more stable, the hollow fiber membrane is not easy to collapse, and the hollow fiber membrane has good pressure resistance, and the whole hollow fiber membrane has good tensile strength; meanwhile, the hollow fiber membrane has uniform hole distribution and proper porosity, so that the hollow fiber membrane has higher water conversion efficiency.

Still further, the thickness of the hollow fiber membrane is 80-150 μm, and the inner diameter of the hollow fiber is 0.7-1.2mm.

The thickness and the inner diameter of the hollow fiber membrane can be measured by performing shape characterization on the hollow fiber membrane structure by using a scanning electron microscope, and then performing calculation after measuring by using computer software (such as Matlab, NIS-Elements and the like) or manually; the above parameters can also be obtained by other measuring means by a person skilled in the art, which are only for reference.

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 easy to deform under extrusion. 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 inner diameter of the hollow fiber membrane is larger, the whole mechanical strength of the 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 internal diameter of the hollow fiber membrane is smaller, the introduction amount of dry air in the internal diameter 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 a proper inner diameter, so that the hollow fiber membrane has sufficient mechanical strength, and further has the effects of pressure resistance and deformation resistance; 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.

To sum up, the internal diameter of the hollow fiber membrane and the thickness of the hollow fiber membrane that this application is suitable make the hollow fiber membrane not only have good resistance to deformation effect and withstand voltage effect, still have good humidification effect.

Furthermore, the outer surface is provided with a plurality of first holes in a circular hole shape; the first holes have a hole area ratio of 12% to 55% on the first outer surface.

It should be noted that the first holes on the outer surface are circular holes, some are circular holes, and some are similar to circular holes, such as oval holes. When the area ratio of the first holes on the first surface is too large, the mechanical strength of the outer surface is reduced, so that the outer surface is easy to damage and has poor pressure resistance; when the hole area ratio of first hole is undersize, reduced the throughput of steam, and then reduced water conversion efficiency, reduced the roughness of surface simultaneously, and then increased gaseous throughput.

In the application, the outer surface has a proper hole area rate, so that the mechanical strength of the outer surface is ensured, and the service life is prolonged; meanwhile, the amount of water vapor entering the hollow fiber membrane is increased, so that the water conversion efficiency is improved, and the throughput of gas is reduced.

Still further, the main body also comprises a plurality of moisture permeable holes, and the average pore diameter of the moisture permeable holes is 1.8-5.2 μm, preferably 2.5-4.5 μm.

It should be noted that the number of moisture permeable pores is small; wherein, the leather layer area has no moisture permeable hole, thus avoiding increasing the gas throughput of the hollow fiber membrane; the average pore diameter of the moisture permeable pores is larger than that of the outer surface, namely the pore diameter of the moisture permeable pores is relatively larger, so that the porosity of the hollow fiber membrane is improved, the throughput of water vapor is increased, and the humidifying efficiency of the membrane is further increased; and the number of moisture permeable holes is small, so that the tensile strength of the film is not influenced.

Furthermore, the tensile strength of the hollow fiber membrane is 4-9MPa, the elongation is 40-120%, the air flux is 10-25ml/min/m2@80KPa, the implosion pressure is more than 500kpa, and the water conversion efficiency is 40-65%.

Important indexes for evaluating the mechanical strength of the hollow fiber membrane are 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 is said to be. Tensile strength refers to the ability of a film to withstand parallel stretching. When the film sample is tested under certain conditions, the film sample is acted by tensile load until the film sample is broken, and the tensile strength and the elongation at break of the film can be calculated according to the maximum tensile load corresponding to the broken film sample, the change of the size (length) of the film sample and the like. The tensile strength and the elongation at break can be measured by a universal tensile testing machine, and the tensile strength of the filter membrane is 4-9MPa; the elongation at break is 40-120%, and the internal detonation pressure is greater than 500kpa, which shows that the hollow fiber membrane has high tensile strength and elongation at break, good pressure resistance, good mechanical property and high industrial practical value, and can completely meet the market demand.

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 air in the present application is 10-25ml/min/m ² @80KPa, its flux is small, indicating that hollow fiber membrane air permeation flux is small; the hollow fiber membrane provided by the application has a transmission coefficient of 0.52-0.56g/cm ² and/MPa, the water conversion efficiency is 40-65%, the higher water conversion efficiency is ensured, and meanwhile, the air throughput is smaller, so that the hollow fiber membrane has a good humidifying effect.

On the other hand, the preparation method of the hollow fiber membrane with high moisture permeability and low air permeability sequentially comprises the following steps:

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 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 60-100%.

S2: and 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: and pre-phase separation, namely, passing the molded product through an air section for pre-phase separation, wherein the humidity of the air section is 50-100%, and the pre-phase separation time is 0.1-2s.

S4: and (3) 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 30-60 ℃, the re-phase separation 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.

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

Further, in the step S1, the temperature of the casting solution is 30-70 ℃, and the temperature of the core solution is 20-30 ℃. The temperature of the spinning nozzle is the same as that of the membrane casting liquid, so that the temperature of the membrane casting liquid is prevented from being influenced by overhigh temperature of the spinning nozzle, the temperature of the core liquid is further influenced, and the phase splitting of the inner surface of the membrane casting liquid is further influenced. The extrusion temperature of the die head is at least 10 ℃ higher than the temperature of the core liquid, the temperature of the core liquid is lower than the extrusion temperature of the die head, so that a compact surface is formed on the inner surface of the film, and if the temperature of the core liquid is too low, a formed skin layer is thicker, so that the humidifying performance of the film is influenced; if the core liquid temperature is too high, the skin layer formed by the film is thinner, and the mechanical performance of the film is further reduced.

Still further, the stretching rate in the step S5 is 3-12m/min, and the raw film is stretched by 1-5 times.

Still further, the casting solution also comprises 1-3 parts of a non-solvent, wherein the weight of the non-solvent is not more than 4% of that of the first organic solvent; the non-solvent is at least one of water, ethanol and isopropanol.

In the method, a casting solution and a core solution are prepared, wherein the casting solution comprises a polysulfone polymer, a hydrophilic additive and a first organic solvent, 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 small pore diameter and gradient change is more easily formed, and the hydrophilicity of the prepared hollow fiber membrane is increased; a small amount of sulfonated polyether sulfone is added into the membrane casting solution, so that the hydrophilicity of the membrane can be further increased, 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 casting solution can be adjusted by adding sulfonated polyethersulfone. A small amount of non-solvent (water, ethanol, isopropanol and the like) is added into the casting solution, so that the casting solution becomes partially turbid (a small amount of small PES particles are formed), the small particles play a role of nucleating agent in the phase separation process, the nucleation and growth rate of the membrane are accelerated, and a relatively loose macroporous structure, namely the formation of moisture permeable pores, is easily formed. If the content of the non-solvent is too large, the number of moisture permeable pores tends to increase, the average pore diameter of the moisture permeable pores increases, the gas passing amount of the hollow fiber membrane increases, the mechanical strength decreases, and the performance of the hollow fiber membrane decreases.

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 casting solution 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 casting solution, the temperature of the spinning nozzle is prevented from being influenced by the overhigh temperature of the spinning nozzle, the temperature of the casting solution is higher than that of the core liquid, the phase splitting of the inner surface is accelerated, and meanwhile, the phase splitting is accelerated by increasing the content of the non-solvent of the core liquid to enable the core liquid to be close to the inner surface to perform rapid phase splitting, so that the phase splitting is further accelerated, and the inner surface forms a compact surface. 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. Placing the formed product with inner and outer surfaces in high humidity air flow to form large hole structure near the outer surface and the outer surface, making the average hole diameter along the film thickness direction change in gradient, placing the formed product in coagulating bath for phase separation, making the coagulating bath permeate from the outer surface to the inner surface along the film thickness direction, and making the phase separation to ensure that the first organic solvent is fully separated out. The infiltration amount of the coagulating bath to the inner surface of the hollow fiber membrane is gradually reduced, and the infiltration speed is gradually slowed down, so that the average pore diameter from the outer surface area to the area close to the inner surface of the hollow fiber membrane is reduced in a gradient manner. The coagulating bath permeates into the hollow fiber membrane along the pore canal formed on the outer surface of the pre-divided phase, and further the first organic solvent is separated out to increase the porosity of the membrane. Since the infiltration speed is slower and the infiltration amount is less and less, the pore diameter of the formed pores is gradually reduced, and therefore, the average pore diameter from the outer surface to the inner surface in the thickness direction of the film is 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.

On the other hand, the hollow fiber membrane is applied to a humidifier of a fuel cell, the humidifier comprises a housing and a hollow fiber membrane bundle positioned in the housing, the hollow fiber membrane bundle is composed of a plurality of hollow fiber membranes with high moisture permeability and low air permeability, two ends of the hollow fiber membrane bundle form sealing parts through potting materials respectively, and the hollow fiber membrane bundle is fixed at two ends of the housing in a sealing mode through the sealing parts, the housing is provided with a first inlet, a first outlet, a second inlet and a second outlet, the first inlet and the first outlet are communicated with a space between the interior of the housing and the periphery of the hollow fiber membrane bundle and are used for flowing through a first fluid, the second inlet and the second outlet are communicated with the interior of the hollow fibers and are used for flowing through a second fluid, and the sealing parts separate the first fluid from the second fluid. Wherein the first fluid is a wet gas with a high water vapor content and the second fluid is a dry gas with a low water vapor content. During the working process of the humidifier, moisture with high water vapor content flows in from the first inlet and enters the space between the inside of the shell and the periphery of the hollow fiber membrane bundle, the water vapor diffuses towards the hollow fiber membrane bundle, other gases in the moisture diffuse towards the direction of the first outlet, dry gas flows in from the second inlet, enters the hollow inside of each hollow fiber and takes away the water vapor diffusing to the hollow fiber membrane, and flows towards the direction of the second outlet, so that the humidifying effect is achieved.

The following beneficial effects can be brought through the application: compared with the existing hollow fiber membrane structure, the hollow fiber membrane provided by the application shows better water conversion efficiency, lower gas throughput and better tensile strength, and can run for a long time at high temperature and high pressure. 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.

Description of the drawings:

FIG. 1 is a Scanning Electron Microscope (SEM) image of the cross section of a high moisture-permeable, low air-permeable hollow fiber membrane prepared in example 1, wherein the magnification is 1000X;

FIG. 2 is a Scanning Electron Microscope (SEM) image of a longitudinal section of a capillary condensation layer of a high moisture-permeable low-permeability hollow fiber membrane prepared in example 1, wherein the magnification is 2000X;

FIG. 3 is a Scanning Electron Microscope (SEM) image of a longitudinal section of a high moisture-permeable low-permeability hollow fiber membrane support layer prepared in example 1, at a magnification of 2000 ×;

FIG. 4 is a Scanning Electron Microscope (SEM) image of the inner surface of the high moisture-permeable low-permeability hollow fiber membrane prepared in example 1, at a magnification of 50000 ×;

FIG. 5 is a Scanning Electron Microscope (SEM) image of the outer surface of a high moisture-permeable, low air-permeable hollow fiber membrane prepared in example 1, at 2000 magnification;

FIG. 6 is a Scanning Electron Microscope (SEM) image of the cross section of a high moisture-permeable, low air-permeable hollow fiber membrane prepared in example 4, at 1000 magnification;

FIG. 7 is a Scanning Electron Microscope (SEM) image of a longitudinal section of a capillary condensation layer of a high moisture-permeable low-permeability hollow fiber membrane prepared in example 4, wherein the magnification is 5000 ×;

FIG. 8 is a Scanning Electron Microscope (SEM) image of a longitudinal section of a high moisture-permeable low-permeability hollow fiber membrane support layer prepared in example 4 at a magnification of 1500;

FIG. 9 is a Scanning Electron Microscope (SEM) image of the inner surface of the high moisture-permeable low-air-permeable hollow fiber membrane prepared in example 4, wherein the magnification is 50000X;

FIG. 10 is a Scanning Electron Microscope (SEM) image of the outer surface of a high moisture permeability low air permeability hollow fiber membrane prepared in example 4 at 2000 magnification;

FIG. 11 is a Scanning Electron Microscope (SEM) image of a longitudinal section of a capillary condensation layer of a high moisture-permeable low-permeability hollow fiber membrane prepared in example 8, at a magnification of 5000 ×;

FIG. 12 is a Scanning Electron Microscope (SEM) image of a longitudinal section of a high moisture-permeable low-permeability hollow fiber membrane support layer prepared in example 8 at 5000X magnification;

FIG. 13 is a Scanning Electron Microscope (SEM) image of the inner surface of the high moisture-permeable low-air-permeable hollow fiber membrane obtained by preparation in example 8, wherein the magnification is 20000 ×;

FIG. 14 is a Scanning Electron Microscope (SEM) image of the outer surface of a high moisture permeability, low air permeability hollow fiber membrane prepared in example 8 at 2000 magnification;

fig. 15 is a polysulfone-based hollow fiber membrane humidifier.

Reference numerals:

1. a first inlet; 2. a first outlet; 3. a second inlet; 4. a second outlet.

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 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

Embodiment 1 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 15 parts of polyether sulfone, 12 parts of polyethylene glycol, 60 parts of dimethyl sulfoxide and 4 parts of sulfonated polyether sulfone;

the core liquid comprises 90% of water and 10% of dimethylformamide;

s2: spinning, namely extruding the casting solution with the temperature of 35 ℃ and the core solution with the temperature of 22 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface; the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely performing pre-phase separation on the molded product for 1s in an air section with the humidity of 80%;

s4: the pre-phase-separated molded product was placed in a coagulation bath at 35 ℃ for 45 seconds to re-phase, thereby forming a green film. Wherein 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 raw membrane by 2.5 times at the stretching speed of 5m/min, cleaning the raw membrane in water, and finally drying to obtain the hollow fiber membrane.

Example 2

Embodiment 2 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 17 parts of polysulfone, 14 parts of polyvinylpyrrolidone, 76 parts of N-ethyl pyrrolidone and 1.5 parts of sulfonated polyether sulfone;

the bore fluid comprises 25 percent of N-ethyl pyrrolidone and 75 percent of water;

s2: spinning, namely extruding the casting solution with the temperature of 48 ℃ and the core solution with the temperature of 23 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface, wherein the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely performing pre-phase separation on the molded product for 0.5s through an air section with the humidity of 92%;

s4: and placing the pre-phase-separated molded product into a coagulating bath at the temperature of 55 ℃ for 36s of re-phase separation to form a green film. Wherein the coagulating bath is a mixture of water and N-ethyl pyrrolidone, and the water content in the coagulating bath is 75%;

s5: and (3) stretching the raw membrane by 2.8 times at the stretching speed of 7m/min, cleaning in water, and finally drying to obtain the hollow fiber membrane.

Example 3

Embodiment 3 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 16 parts of polyether sulfone, 9 parts of polyethylene glycol, 65 parts of dimethyl sulfoxide and 4.5 parts of sulfonated polyether sulfone;

the core liquid comprises 83% of water and 17% of dimethylformamide;

s2: spinning, namely extruding the casting solution with the temperature of 43 ℃ and the core solution with the temperature of 25 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface; the temperature of the spinning nozzle is the same as that of the casting solution.

S3: pre-phase separation, namely performing pre-phase separation on the molded product for 1.5s in an air section with the humidity of 85%;

s4: the pre-phase separated molded product was placed in a coagulation bath at 40 ℃ for 36 seconds to re-phase, and a green film was formed. Wherein the coagulating bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulating bath is 75%;

s5: and (3) stretching the raw membrane by 3 times at the stretching speed of 5.6m/min, cleaning in water, and finally drying to obtain the hollow fiber membrane.

Example 4

Embodiment 4 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 18 parts of polyether sulfone, 1 part of sulfonated polyether sulfone, 15 parts of polyvinylpyrrolidone and 70 parts of dimethylformamide;

the core liquid comprises 20% of N-ethyl pyrrolidone and 80% of water;

s2: spinning, namely extruding the casting solution with the temperature of 40 ℃ and the core solution with the temperature of 24 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface, wherein the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely, pre-phase separation is carried out on the molded product for 4s through an air section with the humidity of 70%;

s4: and (3) placing the pre-phase-separated molded product into a coagulating bath at the temperature of 45 ℃ for 30s of phase separation to form a raw film. Wherein the coagulating bath is a mixture of water and dimethylformamide, and the water content in the coagulating bath is 80%;

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

Example 5

Embodiment 5 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 24 parts of polyarylsulfone, 13 parts of polyethylene glycol, 74 parts of N-methylpyrrolidone and 2 parts of sulfonated polyether sulfone;

the bore fluid comprises 13% and 83% of water;

s2: spinning, namely extruding the casting solution with the temperature of 38 ℃ and the core solution with the temperature of 25 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface, wherein the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely, pre-phase separation is carried out on the molded product for 5.5 seconds through an air section with the humidity of 55%;

s4: placing the pre-phase-separated molded product into a coagulating bath at 43 ℃ for 35s of re-phase separation to form a raw film, wherein the coagulating bath is a mixture of water and dimethyl sulfoxide, and the water content in the coagulating bath is 83%;

s5: and (3) stretching the raw membrane by 4.5 times at the stretching speed of 9m/min, cleaning in water, and finally drying to obtain the hollow fiber membrane.

Example 6

Embodiment 6 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 20 parts of polyarylsulfone, 18 parts of polyethyleneimine, 65 parts of N-ethyl pyrrolidone and 2 parts of sulfonated polyether sulfone;

the bore fluid comprises 32% of dimethylformamide and 68% of water;

s2: spinning, namely extruding the casting solution with the temperature of 45 ℃ and the core solution with the temperature of 26 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface, wherein the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely, pre-phase separation is carried out on the molded product for 2 seconds through an air section with the humidity of 85%;

s4: and (3) placing the pre-phase-separated molded product into a coagulating bath at the temperature of 50 ℃ for 25s of re-phase separation to form a raw film. Wherein the coagulating bath is a mixture of water and dimethylformamide, and the water content in the coagulating bath is 85%;

s5: and (3) stretching the raw membrane by 3.5 times at the stretching speed of 10m/min, cleaning in water, and finally drying to obtain the hollow fiber membrane.

Example 7

Embodiment 7 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 23 parts of polyether sulfone, 1.7 parts of sulfonated polyether sulfone, 16 parts of polyethyleneimine and 67 parts of dimethylacetamide;

the bore fluid comprises 35% of dimethylformamide and 65% of water;

s2: spinning, namely extruding the casting solution with the temperature of 50 ℃ and the core solution with the temperature of 27 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface, wherein the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely, pre-phase separation is carried out on the molded product for 3 seconds through an air section with the humidity of 60%;

s4: the pre-phase-separated molded product was placed in a coagulating bath at 54 ℃ for 30 seconds to form a green film. Wherein the coagulation bath is a mixture of water and dimethyl sulfoxide, and the water content in the coagulation bath is 88%;

s5: and (3) stretching the raw membrane by 3.8 times at a stretching speed of 7.3m/min, cleaning the raw membrane in water, and finally drying to obtain the hollow fiber membrane.

Example 8

Embodiment 8 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 22 parts of polyether sulfone, 10 parts of polyvinyl alcohol, 75 parts of dimethylformamide, 2 parts of water and 3 parts of sulfonated polyether sulfone;

the bore fluid comprises 38 percent of N-ethyl pyrrolidone and 62 percent of water;

s2: spinning, namely extruding the casting solution with the temperature of 55 ℃ and the core solution with the temperature of 27 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface, wherein the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely, pre-phase separation is carried out on the molded product for 2.5 seconds through an air section with the humidity of 78%;

s4: and placing the pre-phase-separated molded product into a coagulating bath at the temperature of 40 ℃ for 35s of phase separation to form a green film. Wherein the coagulating bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulating bath is 90%;

s5: and (3) stretching the raw membrane by 4 times at the stretching speed of 6m/min, cleaning in water, and finally drying to obtain the hollow fiber membrane.

Example 9

Embodiment 9 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 19 parts of polysulfone, 9 parts of polyvinylpyrrolidone, 78 parts of N-ethyl pyrrolidone and 2 parts of sulfonated polyether sulfone;

the bore fluid comprises 40% and 60% of water;

s2: spinning, namely simultaneously extruding the casting solution with the temperature of 60 ℃ and the core solution with the temperature of 28 ℃ from a spinning nozzle to form a formed product with an inner surface and an outer surface;

s3: pre-phase separation, namely performing pre-phase separation on the molded product for 0.4s through an air section with the humidity of 95%;

s4: the pre-phase-separated molded product was placed in a coagulation bath at a temperature of 48 ℃ for 50 seconds to form a green film. Wherein the coagulating bath is a mixture of water and dimethylacetamide, and the water content in the coagulating bath is 86%;

s5: and (3) stretching the raw membrane by 3.5 times at the stretching speed of 5.5m/min, cleaning in water, and finally drying to obtain the hollow fiber membrane.

Example 10

As shown in fig. 15, the hollow fiber membrane prepared by the present application is applied to a humidifier of a fuel cell, the hollow fiber membrane bundle is composed of a plurality of hollow fiber membranes with high moisture permeability and low air permeability, during the operation of the humidifier, moisture with high water vapor content flows in from a first inlet 1, enters a space inside a housing and at the periphery of the hollow fiber membrane bundle, water vapor diffuses towards the hollow fiber membrane bundle, other gases in the moisture diffuse towards a first outlet 2, dry gas flows in from a second inlet 3, enters the hollow interior of each hollow fiber, takes away the water vapor diffusing to the hollow fiber membrane, and flows towards a second outlet 4, thereby achieving the humidification effect.

Comparative example 1

The comparative example 1 provides a polysulfone-based hollow fiber membrane prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 15 parts of polyether sulfone, 6 parts of polyvinylpyrrolidone and 60 parts of dimethylformamide;

the core liquid comprises 90% of water and 10% of dimethylformamide;

s2: spinning, namely extruding the casting solution with the temperature of 35 ℃ and the core solution with the temperature of 22 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface; the temperature of the spinning nozzle is the same as that of the casting solution.

S3: pre-phase separation, namely performing pre-phase separation on the molded product for 1s in an air section with the humidity of 80%;

s4: and placing the pre-phase-separated molded product into a coagulating bath at the temperature of 35 ℃ for 45s of re-phase separation to form a green film. Wherein the coagulating bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulating bath is 70%;

s5: and (3) carrying out 2.5 times of stretching treatment on the raw membrane at the stretching speed of 5m/min, cleaning the raw membrane in water, and finally drying to obtain the hollow fiber membrane.

Under the condition that the parameters of other steps of the comparative example 1 and the example 1 are the same, the sulfonated polyether sulfone is not added, so that the first water contact angles of the inner surface and the outer surface of the hollow fiber membrane are increased, the hydrophobicity of the hollow fiber membrane is increased, the water conversion efficiency is too low, and the requirement of practical application cannot be met.

Comparative example 2

Comparative example 2 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 45 parts of polyether sulfone, 7 parts of polyethylene glycol, 60 parts of dimethyl sulfoxide and 4 parts of sulfonated polyether sulfone;

the core liquid comprises 99% of water and 1% of dimethylformamide;

s2: spinning, namely extruding the casting solution with the temperature of 35 ℃ and the core solution with the temperature of 22 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface; the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely performing pre-phase separation on the molded product for 1s in an air section with the humidity of 80%;

s4: and placing the pre-phase-separated molded product into a coagulating bath at the temperature of 35 ℃ for 45s of re-phase separation to form a green film. Wherein 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 raw membrane by 2.5 times at the stretching speed of 5m/min, cleaning the raw membrane in water, and finally drying to obtain the hollow fiber membrane.

In the comparative example 2, under the condition that the parameters of other steps are the same as those of the example 1, the content of the polyether sulfone is increased, so that the thickness of a skin zone is increased, the water conversion efficiency is too low, and the requirements of practical application cannot be met.

Comparative example 3

The comparative example 3 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 15 parts of polyether sulfone, 7 parts of polyethyleneimine, 60 parts of dimethyl sulfoxide and 4 parts of sulfonated polyether sulfone;

the core liquid comprises 40% of water and 60% of dimethylformamide;

s2: spinning, namely extruding the casting solution with the temperature of 35 ℃ and the core solution with the temperature of 22 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface; the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely performing pre-phase separation on the molded product for 8s in an air section with the humidity of 100%;

s4: the pre-phase-separated molded product was placed in a coagulation bath at 35 ℃ for 45 seconds to re-phase, thereby forming a green film. Wherein the coagulating bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulating bath is 70%;

s5: and (3) carrying out 2.5 times of stretching treatment on the raw membrane at the stretching speed of 5m/min, cleaning the raw membrane in water, and finally drying to obtain the hollow fiber membrane.

In the comparative example 3, under the condition that the parameters of other steps are the same as those of the example 1, the content of the non-solvent in the core liquid is reduced, the pore structure of the inner surface is increased, the porosity of the skin layer area is increased, and the air permeability is too high to meet the requirements of practical application.

Comparative example 4

Comparative example 4 provides a polysulfone-based hollow fiber membrane, which is prepared by the following method:

s1, preparing a casting solution and a core solution;

the casting solution comprises the following substances in parts by weight: 15 parts of polyether sulfone, 12 parts of polyvinyl alcohol, 60 parts of dimethylacetamide and 4 parts of sulfonated polyether sulfone;

the core liquid comprises 90% of water and 10% of dimethylformamide;

s2: spinning, namely extruding the casting solution with the temperature of 35 ℃ and the core solution with the temperature of 22 ℃ from a spinning nozzle simultaneously to form a formed product with an inner surface and an outer surface; the temperature of the spinning nozzle is the same as that of the casting solution;

s3: pre-phase separation, namely performing pre-phase separation on the molded product for 0.3s in an air section with the humidity of 35%;

s4: and placing the pre-phase-separated molded product into a coagulating bath at the temperature of 35 ℃ for 10s of re-phase separation to form a green film. Wherein the coagulating bath is a mixture of water and N-methylpyrrolidone, and the water content in the coagulating bath is 40%;

s5: and (3) carrying out 2.5 times of stretching treatment on the raw membrane at the stretching speed of 5m/min, cleaning the raw membrane in water, and finally drying to obtain the hollow fiber membrane.

In the comparative example 4, under the condition that the parameters of other steps are the same as those in the example 1, the humidity of air in the pre-divided phase is reduced, a skin layer area is formed in an area close to the outer surface, the average pore diameter of the outer surface is not more than 100nm, the average pore diameter change gradient is too small, the porosity is too low, the water conversion rate is too low, and the requirement of practical application cannot be met.

Performance test

Structural characterization

The hollow fiber membranes obtained in each example and comparative example were subjected to the morphological characterization of the longitudinal section, inner surface and outer surface, the measurement of the thickness and average pore diameter of each layer in the bulk, and the measurement of the average fiber diameter and porosity of the hollow fiber membranes, respectively, wherein the measurement data are shown in tables 1 to 2, and the morphological characterization results of examples 1 to 8 are shown in fig. 1 to 14.

Table 1 characterization of each example membrane structure

TABLE 2 characterization of the hollow fiber membrane structures for each example

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1. Performance test

The hollow fiber membranes obtained in each example were subjected to tensile property tests.

Experimental equipment: tension tester

Preparation before testing: the hollow fiber membrane to be tested is cut to be 10cm long.

The testing steps are as follows: and vertically clamping the membrane filaments at the upper end and the lower end of a chuck, wherein the distance between the chucks at the two ends is controlled to be 5cm. The mode was selected on the instrument operated to give tensile strength and elongation.

And (4) calculating a result: tensile strength:

in the formula: σ -tensile strength in MegaPascals (MPa); fb-the maximum force experienced at snap in (N); so-original cross-sectional area of the sample in (mm) ² ) (ii) a The instrument is indicated by "sample area S".

Elongation percentage:

in the formula: e-elongation; Δ L-the increment in length between gauge lengths of the test specimen in millimeters (mm); l-gauge length of the sample in millimeters (mm).

Table 3 tensile properties test results for each example

It should be noted that, the same sample has a plurality of test points, and as a result, the average value of the plurality of test points has non-uniformity, so the point values corresponding to the respective test points may be different.

The hollow fiber membranes obtained in each example were tested for internal and external surface contact angles.

Experimental equipment: contact angle tester

Preparation before testing: and cutting a small section of the hollow fiber membrane yarn open, flattening the cut hollow fiber membrane yarn, and fixing the flattened hollow fiber membrane yarn on the double-faced adhesive tape.

The testing steps are as follows: and (3) placing the fixed hollow fiber membrane wire on a clamp of a contact angle tester, observing the change of the contact angle through the change of pure water drops on the hollow fiber membrane wire, and obtaining the data of the first water contact angle.

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

Experimental equipment: digital display pressure gauge, gas flowmeter and digital display hygrothermograph

Preparation before testing: self-made hollow fiber small component

The testing steps are as follows: the homemade hollow fiber small module is fixed on the test bench, the wet air with a set flow enters from the wet in end, and is monitored by a digital display hygrothermograph, wherein the humidity needs to be controlled within 90-96% RH.

And the other path of dry air with a certain flow enters from the dry in end and is monitored by a digital display hygrothermograph. 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 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 a 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 in units of (m) ³ )。

In the formula: omega-water conversion efficiency, m ₁ Water content at the dry out end of the hollow fiber membrane in (g), m 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 test

Experimental equipment: gas flowmeter

Preparation before testing: self-made hollow fiber small component

The testing steps are as follows: and blocking the wet out end and dry out end of the self-made single hollow fiber membrane wire small assembly. Compressed air is introduced from the wet in end, and the number of the wet in end display pressure is ensured to be stabilized at 80kpa. And a digital display gas flowmeter is connected to the dry in end to measure the air permeability. (for the condition that the gas permeability is very small, the number of bubbles in a certain time can be counted) and the data is recorded.

Table 4 test results of hydrophilicity, water conversion efficiency and air permeability amount for 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 (19)

1. A hollow fiber membrane with high moisture permeability and low air permeability comprises a main body, wherein one side of the main body is an inner surface, the other side of the main body is an outer surface, and a non-directional tortuous passage is arranged in the main body, and the hollow fiber membrane is characterized in that:

the average pore diameter of the main body is in gradient change from the area close to the outer surface to the area close to the inner surface;

the main body comprises a capillary condensation layer and a supporting layer, wherein 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 support layer are transited by continuous fibers;

the average pore diameter of the outer surface is 200-650nm; the inner surface is a dense surface.

2. The hollow fiber membrane with high moisture permeability and low air permeability according to claim 1, wherein the average pore diameter variation gradient of the hollow fiber membrane is 2-8nm/μm, and the porosity of the hollow fiber membrane is 60% -85%.

3. The high moisture permeable low air permeable hollow fiber membrane of claim 1, wherein the first water contact angle of the inner surface is 8-35 ° smaller than the first water contact angle of the outer surface;

preferably, 12-32 ° smaller; more preferably, 15-28 °;

and the first water contact angle from the inner surface to the outer surface in the thickness direction of the film is changed in a gradient manner.

4. The hollow-fiber membrane with high moisture permeability and low air permeability according to claim 3, wherein the first water contact angle of the inner surface is 45 to 75 ° and the first water contact angle of the outer surface is 60 to 89 °.

5. The hollow fiber membrane with high moisture permeability and low air permeability according to claim 1, wherein the thickness of the capillary condensation layer is 8-25 μm, and the percentage of the thickness of the hollow fiber membrane body is 8-20%.

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

7. The hollow-fiber membrane with high moisture permeability and low air permeability according to claim 1, wherein the average pore diameter of the capillary condensation layer is 20-120nm, and the porosity of the capillary condensation layer is 15% -50%.

8. The high moisture-permeable, low air-permeable hollow fiber membrane according to claim 1, wherein the capillary condensation layer comprises a skin region, one side of which is an inner surface;

the thickness of the skin region accounts for 15% -25% of the thickness of the capillary condensation layer, and the porosity of the skin region is not more than 10%.

9. The hollow fiber membrane of high moisture permeability and low air permeability of claim 1, wherein said body comprises fibers forming a porous structure, said fibers being a striped structure;

the fibers have an average diameter of 200 to 500nm.

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

11. The hollow fiber membrane with high moisture permeability and low air permeability according to claim 1, wherein the outer surface is provided with a plurality of first holes in the shape of round holes; the first holes have a hole area ratio of 12% -55% on the first outer surface.

12. The hollow fiber membrane with high moisture permeability and low air permeability according to claim 1, wherein the main body further comprises a plurality of moisture permeable pores, and the average pore diameter of the moisture permeable pores is 1.8-5.2 μm.

13. The hollow fiber membrane with high moisture permeability and low air permeability according to claim 1, wherein the air permeability of the hollow fiber membrane is 10-25ml/min/m ² @80KPa, implosion pressure more than 500KPa, water conversion efficiency of 40-65%, tensile strength of 4-9MPa and elongation of 40-120%.

14. The method for preparing a hollow fiber membrane with high moisture permeability and low air permeability according to any one of claims 1 to 13, comprising the following steps in sequence:

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 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 60-100%;

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 humidity of the air section is 50-100%, and the pre-phase separation time is 0.1-6s;

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 30-60 ℃, 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.

15. A preparation method according to claim 14, wherein the casting solution further comprises 1-3 parts of a non-solvent, the weight of the non-solvent not exceeding 4% of the weight of the first organic solvent; the non-solvent is at least one of water, ethanol and isopropanol.

16. The method of claim 14, wherein 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;

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

17. The method according to claim 14, wherein the temperature of the dope solution in step S1 is 30 to 70 ℃ and the temperature of the dope solution in the core is 20 to 30 ℃, and the temperature of the spinning nozzle is the same as the temperature of the dope solution in step S2, and the die extrusion temperature is at least 10 ℃ higher than the temperature of the dope solution in the core.

18. The method according to claim 14, wherein the stretching rate in step S5 is 3 to 12m/min, and the raw film is stretched 1 to 5 times.

19. Use of a hollow fiber membrane with high moisture permeability and low gas permeability according to any one of claims 1 to 13 in a humidifier for 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 hollow fiber membranes with high moisture permeability and low gas permeability according to any one of claims 1 to 13, both ends of the hollow fiber membrane bundle forming a sealing portion by potting material, respectively, and being sealingly fixed to both ends of the housing by the sealing portions, the housing having 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) communicating with a space between the inside of the housing and the outer periphery of the hollow fiber membrane bundle for a first fluid to flow through, the second inlet (3) and the second outlet (4) communicating with the inside of the hollow fiber for a second fluid to flow through, the sealing portion separating the first fluid from the second fluid.

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