CN113926316B - Leakage-proof humidifying composite hollow fiber membrane, preparation method and application thereof - Google Patents
Leakage-proof humidifying composite hollow fiber membrane, preparation method and application thereof Download PDFInfo
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- B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M8/00—Fuel cells; Manufacture thereof
- H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
- H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
- H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
- H01M8/04119—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with simultaneous supply or evacuation of electrolyte; Humidifying or dehumidifying
- H01M8/04126—Humidifying
- H01M8/04149—Humidifying by diffusion, e.g. making use of membranes
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Abstract
The invention provides a leak-proof humidifying composite hollow fiber membrane, a preparation method and application thereof. The leak-proof humidifying composite hollow fiber membrane comprises an outer hydrophilic layer and an inner hydrophobic layer attached to the inner surface of the outer hydrophilic layer, wherein the outer hydrophilic layer is provided with a spongy pore structure, the pore diameter of the outer surface of the outer hydrophilic layer is changed from the outer surface to the inner surface from large to small, and the thickness of the inner hydrophobic layer of the leak-proof humidifying composite hollow fiber membrane is smaller than that of the outer hydrophilic layer. The leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer which are asymmetric in structure is prepared by the invention, the thickness of the inner hydrophobic layer of the membrane is smaller than that of the outer hydrophilic layer, and one side of the membrane is hydrophilic, and the other side of the membrane is hydrophobic, so that the membrane has asymmetric hydrophilic/hydrophobic dual-performance, is a novel membrane for humidifying fuel cells, is beneficial to capturing and permeation of water molecules, and is beneficial to escape of water vapor.
Description
Technical Field
The invention belongs to the technical field of polymer membranes, and particularly relates to a leakage-proof humidifying composite hollow fiber membrane, a preparation method and application thereof.
Background
Along with the rapid development of society, an electrochemical fuel cell is considered as a novel power generation technology with the most development prospect in the current generation, can directly convert chemical energy into heat energy, and has the unique advantages of no noise, environmental protection, high reliability, easy maintenance and the like. Proton exchange membrane fuel cells can utilize proton conducting materials as electrolytes, i.e., proton conductivity is closely related to the water content in the proton exchange membrane. When the proton exchange membrane is at a lower humidity, the conductivity of the proton exchange membrane is greatly reduced, so that the performance of the battery cannot be fully exerted. Therefore, it is necessary to secure battery performance by means of a humidification system, and compared with a self-humidification technology which is small in humidification amount and is not suitable for industrial application, an external membrane method humidification technology is gradually widely applied.
The membrane humidifier is widely applied in the membrane external humidification technology because of no external force driving and the like, and the principle is that one side of a humidifying membrane is mainly used for humidifying a battery system by dry and cold fuel gas, the other side of the membrane is used for humidifying a battery system by wet and hot fuel tail gas and the concentration difference of the two sides of the humidifying membrane. As the core component of the membrane humidifier, the traditional hydrophilic membrane, compact membrane, physical asymmetric membrane and the like are widely studied, as the invention patent CN1621136a discloses a cellulose hollow fiber gas humidification membrane with a homogeneous compact structure, the membrane has high mechanical strength, stronger organic solvent resistance, acid-base resistance and water permeability, however, for a fuel cell system, when the water content in the proton exchange membrane is too high, the electrode is submerged, and the normal operation of the fuel cell is not facilitated; the invention patent CN106674562A discloses a polyvinyl alcohol film with a hydrophobic structure and a preparation method thereof, and compared with similar polyvinyl alcohol films, the loose polyvinyl alcohol film has better water and gas permeability, and has better dimensional stability in a good solvent environment of the polyvinyl alcohol, however, the polyvinyl alcohol has excellent affinity with water molecules, is easy to absorb and diffuse the water molecules, is not easy to escape, and has unsatisfactory humidifying effect; the invention patent CN106378014A discloses a composite humidifying membrane based on an asymmetric structure and a preparation method thereof, and the composite membrane has a composite structure, but only involves coating hydrophilic polymer on the surface of porous layer polymer, namely the porous layer polymer has the asymmetry of a physical structure, and the thickness of the hydrophilic layer polymer is conceivable to be far smaller than that of the porous layer polymer, so that the larger transmembrane resistance is not beneficial to the diffusion of water molecules, and the humidifying effect is not ideal.
Disclosure of Invention
Aiming at the problems of electrode submerged caused by too high humidity, low power generation efficiency caused by poor humidifying effect and the like in the working process of the fuel cell in the prior art, the invention aims to provide a leakage-proof humidifying composite hollow fiber membrane, a preparation method and application thereof; the invention provides a method for preparing a hollow fiber membrane with a hydrophilic gradient spongy pore structure, wherein a hydrophilic polymer is used as a base material, the hollow fiber membrane is provided with inner-layer pores with small density and outer-layer pores with large density, and the inner surface of the hollow fiber membrane is modified by a hydrophobic modifier solution to obtain an inner hydrophobic coating so as to meet the requirements of capturing water molecules, permeation, escape of water vapor and the like; the preparation process is simple, the material price is low, no toxic reagent is involved in the experimental process, and the obtained leak-proof humidifying composite hollow fiber membrane with the asymmetric structure of the inner hydrophobic layer and the outer hydrophilic layer has stable humidifying effect and wide application value in the working process of a fuel cell humidifying system.
In order to achieve the above object, the first aspect of the present invention provides a leak-proof humidifying composite hollow fiber membrane, which adopts the following technical scheme:
The leak-proof humidifying composite hollow fiber membrane comprises an outer hydrophilic layer and an inner hydrophobic layer attached to the inner surface of the outer hydrophilic layer, wherein the outer hydrophilic layer is provided with a spongy pore structure, the pore diameter of the outer surface of the outer hydrophilic layer is changed from the outer surface to the inner surface from large to small, and the thickness of the inner hydrophobic layer of the leak-proof humidifying composite hollow fiber membrane is smaller than that of the outer hydrophilic layer.
In the above-mentioned leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the outer surface pore diameter of the outer hydrophilic layer of the leak-proof humidifying composite hollow fiber membrane is 0.1 to 0.3 μm (e.g., 0.12 μm, 0.15 μm, 0.22 μm, 0.25 μm, 0.28 μm), and the surface pore diameter of the inner hydrophobic layer is 0.005 to 0.07 μm (e.g., 0.008 μm, 0.01 μm, 0.02 μm, 0.04 μm, 0.06 μm).
In the invention, the leak-proof humidifying composite hollow fiber membrane has an asymmetric structure of an inner hydrophobic layer and an outer hydrophilic layer, wherein the inner hydrophobic layer is attached to the inner surface of the outer hydrophilic layer, the attachment of the inner hydrophobic layer does not change the pore diameter structure of the outer surface of the outer hydrophilic layer, the outer hydrophilic layer has a spongy pore structure, and the pore diameter of the outer surface of the outer hydrophilic layer is changed from the outer surface to the inner surface to form an inner dense outer hydrophobic structure; the design of the inner hydrophobic layer of the leak-proof humidifying composite hollow fiber membrane is unfavorable for water molecule permeation, but is favorable for water vapor to escape during air blowing; the outer hydrophilic layer of the leak-proof humidifying composite hollow fiber membrane has an outer hydrophobic and inner dense pore structure, the outer surface porous pore structure of the outer hydrophilic layer is beneficial to capturing and penetrating water molecules, the inner surface of the outer hydrophilic layer is dense, water molecules are beneficial to preventing from penetrating the membrane layer, and meanwhile, the thickness of an inner hydrophobic layer is not required to be too thick; the leak-proof humidifying composite hollow fiber membrane can effectively avoid the problem of electrode flooding of a fuel cell caused by overhigh humidity, and has the characteristics of high temperature resistance, water resistance, humidification, contribution to water molecule capturing, permeation, water vapor escape and the like.
In the above-mentioned leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the thickness of the inner hydrophobic layer of the leak-proof humidifying composite hollow fiber membrane is 0.5 to 5.0 μm (e.g., 1.0 μm, 1.5 μm, 2.5 μm, 3.6 μm, 4.5 μm); the thickness of the outer hydrophilic layer is 0.1-0.3 mm (such as 0.15mm, 0.18mm, 0.20mm, 0.22mm, 0.26 mm).
In the above-described leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the contact angle of the inner hydrophobic layer of the leak-proof humidifying composite hollow fiber membrane is greater than 120 ° (such as 122 °, 123 °, 125 °, 128 °, 130 °); the contact angle of the outer hydrophilic layer is less than 30 ° (e.g. 29 °, 27 °, 25 °, 23 °, 21 °).
In the above-described leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the leak-proof humidifying composite hollow fiber membrane is produced by: firstly, preparing spinning casting film liquid into a hollow fiber membrane with an inner-dense outer-spongy pore structure by using an immersion precipitation phase transfer wet spinning or dry-wet spinning technology through core liquid and external coagulation bath regulation and control, and then modifying the inner surface of the hollow fiber membrane with the inner-dense outer-spongy pore structure by using a hydrophobic modifier solution to prepare the leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer asymmetric structure.
In the above leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the hydrophobic modifier solution comprises: 0.1 to 20.0wt% (e.g., 0.2wt%, 2wt%, 5wt%, 10wt%, 15 wt%) of a hydrophobic modifier and 80 to 99.9wt% (e.g., 99.8wt%, 98wt%, 95wt%, 90wt%, 85 wt%) of a solvent; preferably, the hydrophobic modifier is one or more of polydimethylsiloxane, triethoxy fluorosilane, tridecyl fluorooctyl trimethoxysilane and heptadecyl fluorodecyl triethoxysilane; preferably, the solvent is one or more of n-hexane, n-heptane, toluene, xylene and petroleum ether.
In the invention, if the concentration of the hydrophobic modifier in the hydrophobic modifier solution is lower than 0.1 weight percent, the prepared leak-proof humidifying composite hollow fiber membrane has smaller hydrophobic layer thickness and poorer hydrophobicity, is not beneficial to the permeation and separation of water vapor from the composite hollow fiber membrane and is not beneficial to humidification; if the concentration of the hydrophobic modifier in the hydrophobic modifier solution is more than 20wt%, the thickness of the hydrophobic layer in the prepared leak-proof humidifying composite hollow fiber membrane is larger, and the hydrophobic property is too high, so that the water molecules are not easy to capture and permeate.
The selected hydrophobic modifier of the invention is polydimethylsiloxane, triethoxy fluorosilane, tridecyl fluorooctyl trimethoxysilane and heptadecyl fluorodecyl triethoxy silane, has very ideal hydrophobic effect, and particularly the hydrophobic modifiers except polydimethylsiloxane are fluorine-containing hydrophobic modifiers, so that the hydrophobic effect is better, and the water vapor is easy to permeate and separate.
In the above leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the spinning casting solution comprises: 14.0 to 24.0 weight percent of hydrophilic polymer, 56.0 to 84.0 weight percent of organic solvent and 2.0 to 20.0 weight percent of hydrophilic modifier; preferably, the hydrophilic polymer is one or more of cellulose, polysulfone, polyethersulfone, polyether modified polysulfone, sulfonated polyethersulfone and cellulose acetate; preferably, the organic solvent is one or more of dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone; preferably, the hydrophilic modifier is one or more of PEG200, PEG400, PEG800, PEG1000, PEG2000, PVP-K17, PVP-K30, PVP-K60, PVP-K90 and polyvinyl alcohol.
The hydrophilic modifier acts as a pore-forming agent, and the concentration of the hydrophilic modifier can be regulated to obtain the hollow fiber membrane with uniform pore distribution and an inner-dense and outer-spongy pore structure.
In the above leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the core liquid is water, and the external coagulation bath is one or more of water, dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide, and N-methylpyrrolidone; preferably, when the external coagulation bath contains an organic solvent, the organic solvent occupies not more than 80vol% of the external coagulation bath.
In the invention, when the concentration of the organic solvent contained in the external coagulation bath is increased, the phase separation process can be delayed, so that a looser pore structure can be obtained, and the pore diameter of the outer surface of the hollow fiber membrane is larger.
The second aspect of the invention provides a preparation method of the leak-proof humidifying composite hollow fiber membrane, which comprises the following steps: preparing spinning casting solution, preparing a hollow fiber membrane with an inner-dense outer-sparse spongy pore structure by an immersion precipitation phase transfer method, and modifying by a hydrophobic modifier solution to prepare the leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer asymmetric structure.
In the above preparation method of the leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the preparation method of the spinning casting solution specifically comprises the following steps: drying hydrophilic polymer solid powder in vacuum at 40-60 ℃ (such as 42 ℃, 48 ℃ and 55 ℃) to remove water, dissolving the hydrophilic polymer solid powder in an organic solvent, adding a hydrophilic modifier, and mechanically stirring for 6-72 hours (such as 10 hours, 30 hours and 58 hours) and defoaming for 12-72 hours (such as 20 hours, 40 hours and 60 hours) to obtain uniform transparent spinning casting solution, wherein the hydrophilic polymer accounts for 14.0-24.0 wt% (such as 15wt%, 18wt%, 20wt% and 22 wt%) of the spinning casting solution, and the organic solvent accounts for 56.0-84.0 wt% (such as 60wt%, 65wt%, 70wt% and 80 wt%) of the spinning casting solution; the hydrophilic modifier is 2.0-20.0 wt% (such as 5wt%, 12wt%, 15wt%, 18 wt%) of the spinning casting solution.
In the above method for preparing a leak-proof humidified composite hollow fiber membrane, as a preferred embodiment, the hydrophilic polymer solid powder is vacuum-dried at 40 to 60℃such as 42℃at 48℃at 55℃for 24 hours.
In the preparation method of the leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the preparation of the hollow fiber membrane with an inner dense and outer spongy pore structure by the immersion precipitation phase transfer method specifically comprises the following steps: extruding the spinning casting film liquid and the core liquid from a spinneret, controlling the temperature of the core liquid and the temperature of an external coagulation bath to be 30-90 ℃ (such as 40 ℃, 48 ℃, 55 ℃, 70 ℃ and 88 ℃), and sequentially carrying out external coagulation bath gelation, continuous water washing and quick drying after a dry spinning stage of 5-50 cm (such as 10cm, 15cm, 25cm, 32cm and 48 cm) to obtain the hollow fiber film with an internal-dense and external-spongy pore structure.
In the invention, the pore size of the outer hydrophilic layer and the inner surface of the leak-proof humidifying composite hollow fiber membrane can be regulated and controlled by controlling the core liquid temperature and the outer coagulation bath temperature, and the pore structure with inner density and outer hydrophobicity can be obtained.
In the above preparation method of the leak-proof humidifying composite hollow fiber membrane, as a preferred embodiment, the preparation method of the leak-proof humidifying composite hollow fiber membrane with an asymmetric structure of an inner hydrophobic layer and an outer hydrophilic layer by modifying the hydrophobic modifier solution specifically comprises: firstly, packaging a hollow fiber membrane with an inner-dense and outer-spongy pore structure, dissolving a hydrophobic modifier in a solvent to prepare a hydrophobic modifier solution, wherein the hydrophobic modifier accounts for 0.1-20.0wt% (such as 0.2wt%, 2wt%, 5wt%, 10wt%, 15 wt%) of the hydrophobic modifier solution, then flushing the inner surface of the hollow fiber membrane with the inner-dense and outer-spongy pore structure with the hydrophobic modifier solution for 1-5 h (such as 1.5h, 2h, 2.5h, 3.0h, 3.6h and 4.2 h), and then performing heat treatment for 1-5 min (such as 2min, 3min, 3.5min and 4 min) at 80-120 ℃ (such as 85 ℃, 95 ℃, 100 ℃, 110 ℃).
In the invention, after the inner surface of the hollow fiber membrane with the inner dense and outer spongy pore structure is washed by the hydrophobic modifier solution, heat treatment is required to be carried out at the temperature of 80-120 ℃, so that the stability of the inner hydrophobic layer of the prepared leak-proof humidifying composite hollow fiber membrane can be improved.
In the invention, if the flushing time is longer than 5 hours, the thickness of the inner hydrophobic layer of the prepared leak-proof humidifying composite hollow fiber membrane is too thick, so that the inner surface membrane pores of the outer hydrophilic layer are greatly reduced; if the flushing time is less than 1h, the modification time is too short, and the hydrophobic effect is not obvious.
In the preparation method of the leak-proof humidifying composite hollow fiber membrane, as a preferred implementation manner, the encapsulation treatment is to fix a bundle of hollow fiber membranes with inner-dense outer-open spongy pore structures together by using polyurethane glue or modified acrylate adhesive (AB glue) and encapsulate the hollow fiber membranes into an assembly, and after the polyurethane glue or the modified acrylate adhesive (AB glue) is dried, the assembly is cut off by using a cutter to keep the membrane wire port unblocked.
The invention aims to encapsulate a plurality of hollow fiber membranes with inner-dense outer-spongy pore structures into a component so as to realize the purpose of modifying the plurality of hollow fiber membranes by using a hydrophobic modifier solution, simplify the process and facilitate the operation.
In a third aspect, the present invention provides the use of a leak-proof humidification composite hollow fiber membrane for use in a humidification process external to a gas humidification system of a fuel cell.
In a fourth aspect, the present invention provides a membrane humidifier employing a leak-proof humidification composite hollow fiber membrane as a humidification membrane.
Compared with the prior art, the invention has the following advantages:
(1) The leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer which are asymmetric in structure, wherein the thickness of the inner hydrophobic layer of the membrane is smaller than that of the outer hydrophilic layer, and the membrane has the advantages of being different in hydrophilicity/hydrophobicity on two sides, hydrophilic on one side and asymmetrical in hydrophilicity/hydrophobicity on the other side, being a novel membrane for humidifying treatment of fuel cells, being beneficial to capturing and permeation of water molecules and escaping of water vapor.
(2) The leak-proof humidifying composite hollow fiber membrane with the asymmetric structure of the inner hydrophobic layer and the outer hydrophilic layer can realize directional transportation of water to a certain extent, and the inner hydrophobic layer can effectively prevent permeation of water molecules.
(3) The leak-proof humidifying composite hollow fiber membrane with the asymmetric structure of the inner hydrophobic layer and the outer hydrophilic layer has strong hydrophilicity, the aperture of the outer surface of the outer hydrophilic layer is 0.1-0.3 mu m, the aperture of the inner surface of the outer hydrophilic layer is 0.01-0.08 mu m, which is favorable for capturing and transmitting water molecules, and meanwhile, the inner hydrophobic layer is unfavorable for transmitting water molecules, but is easy for water vapor to escape when air passes through, so that the flooding of an electrode of a fuel cell caused by overhigh humidity can be effectively avoided.
(4) The leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer which are in an asymmetric structure, wherein two sides of the membrane are asymmetric hydrophilic/hydrophobic, and the hydrophilic/hydrophobic and water spreading capacities of the hydrophilic/hydrophobic sides of the membrane are obviously different; the contact angle of the outer hydrophilic layer of the bipolar polymer film is smaller than 30 degrees, the contact angle of the inner hydrophobic layer is larger than 120 degrees, and stable humidification effect of the fuel cell can be maintained.
(5) Compared with the self-humidifying technology which has small humidifying amount and is not suitable for industrial application, the preparation technology of the invention has the advantages of simplicity, low material price, no toxic reagent involved in the experimental process, excellent and stable humidifying effect and green and efficient technology.
Drawings
FIG. 1 is a schematic cross-sectional view of an asymmetric leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer according to example 1, (A) the outer hydrophilic layer; (B) an inner hydrophobic layer;
FIG. 2 is a microscopic image (SEM image) of the inner hydrophobic layer of example 1 corresponding to the leak-proof humidifying composite hollow fiber membrane having an asymmetric structure of the inner hydrophobic layer and the outer hydrophilic layer;
fig. 3 is a microscopic image (SEM image) of the outer hydrophilic layer of the leak-proof moisturizing composite hollow fiber membrane corresponding to example 1 having an asymmetric structure of the inner hydrophobic layer and the outer hydrophilic layer.
Detailed Description
The following description of the technical solutions in the embodiments of the present invention will be clear and complete, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which are derived by a person skilled in the art based on the embodiments of the invention, fall within the scope of protection of the invention.
The starting materials described in the examples below are all commercially available from the public. The hydrophilic polymer used in the process of the present invention may be any hydrophilic polymer used in the art for preparing hydrophilic fibrous membranes. However, for convenience of description of the embodiments of the present invention, the hydrophilic polymers of the same name used in the different embodiments of the present invention are the same model or brand of products produced by the same manufacturer.
Example 1 a leak-proof humidifying composite hollow fiber membrane, the preparation method thereof comprises:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 19.0wt% of cellulose acetate powder, 71.0wt% of N, N-dimethylformamide and 10.0wt% of PEG2000, specifically, drying the cellulose acetate powder at 50 ℃ in vacuum for 24 hours to remove water, dissolving the cellulose acetate powder in an N, N-dimethylformamide organic solvent, adding a PEG2000 hydrophilic modifier, mechanically stirring for 36 hours and defoaming for 48 hours to obtain uniform and transparent spinning casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting film liquid prepared in the step (1) from a spinning nozzle together with core liquid at the pressure of 1.0MPa, wherein the core liquid is water, and the external coagulation bath is a mixed solution of water and N, N-dimethylformamide (volume ratio is 1:1); controlling the temperature of the core liquid and the temperature of the external coagulation bath to be 60 ℃, and sequentially carrying out the gelation of the external coagulation bath, continuous water washing and quick drying after a dry spinning stage of 25cm to obtain a hollow fiber membrane with a hydrophilic gradient spongy pore structure with inner density and outer hydrophobicity;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense and outer-hydrophobic hydrophilic gradient sponge porous structure obtained in the step (2), dissolving polydimethylsiloxane in n-hexane to prepare a hydrophobic modifier solution, wherein the polydimethylsiloxane is 10wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 2h, performing heat treatment at 100 ℃ for 2min, and further cleaning and drying to realize hydrophobic modification on only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Example 2 a leak-proof humidifying composite hollow fiber membrane, the method of preparation comprising:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 14.0wt% of cellulose powder, 84.0wt% of N, N-dimethylacetamide and 2.0wt% of PVP-K30, specifically, drying the cellulose powder at 40 ℃ in vacuum for 24 hours to remove water, dissolving the cellulose powder in N, N-dimethylacetamide organic solvent, adding PVP-K30 hydrophilic modifier, mechanically stirring for 6 hours and defoaming for 12 hours to obtain uniform and transparent spinning casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting film liquid prepared in the step (1) from a spinning nozzle together with core liquid at 0.1MPa, wherein the core liquid is water, and the external coagulation bath is a mixed solution of water and N, N-dimethylacetamide (the volume ratio is 2:1); controlling the temperature of the core liquid and the temperature of the external coagulation bath to be 30 ℃, and sequentially carrying out the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like after a dry spinning stage of 5cm to obtain a hollow fiber membrane with a hydrophilic gradient spongy pore structure with inner density and outer hydrophobicity;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense and outer-hydrophobic hydrophilic gradient spongy pore structure obtained in the step (2), dissolving tridecafluorooctyl trimethoxysilane in n-heptane to prepare a hydrophobic modifier solution, wherein the tridecafluorooctyl trimethoxysilane is 0.1wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 1h, performing heat treatment at 80 ℃ for 5min, and further cleaning and drying to realize the hydrophobic modification of only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Example 3 a leak-proof humidifying composite hollow fiber membrane, the method of preparation comprising:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 24.0wt% of polyether modified polysulfone powder, 56.0wt% of N-methylpyrrolidone and 20.0wt% of polyvinyl alcohol, specifically, drying polyether modified polysulfone powder at 60 ℃ in vacuum for 24 hours to remove water, dissolving the polyether modified polysulfone powder in an N-methylpyrrolidone organic solvent, adding a polyvinyl alcohol hydrophilic modifier, mechanically stirring for 72 hours and defoaming for 72 hours to obtain uniform and transparent spinning casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting film liquid prepared in the step (1) from a spinning nozzle together with core liquid at 2.0MPa, wherein the core liquid is water, and the external coagulation bath is a mixed solution of water and N-methylpyrrolidone (volume ratio is 5:1); controlling the temperature of the core liquid and the temperature of the external coagulation bath to be 90 ℃, and sequentially carrying out the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like after a dry spinning stage of 50cm to obtain a hollow fiber membrane with a hydrophilic gradient spongy pore structure with inner density and outer hydrophobicity;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense and outer-hydrophobic hydrophilic gradient spongy pore structure obtained in the step (2), dissolving heptadecafluorodecyl triethoxysilane in xylene to prepare a hydrophobic modifier solution, wherein the heptadecafluorodecyl triethoxysilane is 20.0wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 5h, performing heat treatment at 120 ℃ for 1min, and further cleaning and drying to realize hydrophobic modification of only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Example 4 a leak-proof humidifying composite hollow fiber membrane, the method of making comprising:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 18.0wt% of sulfonated polysulfone powder, 74.5wt% of dimethyl sulfoxide and 7.5wt% of PEG200, specifically, drying the sulfonated polysulfone powder at 60 ℃ in vacuum for 24 hours to remove water, dissolving the sulfonated polysulfone powder in a dimethyl sulfoxide organic solvent, adding a hydrophilic modifier, and mechanically stirring for 48 hours and defoaming for 48 hours to obtain uniform and transparent spinning casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting film liquid prepared in the step (1) from a spinneret together with core liquid at 1.5MPa, wherein the core liquid is water, and the external coagulation bath is a mixed solution of water and dimethyl sulfoxide (volume ratio is 3:1); the core liquid temperature and the external coagulation bath temperature are controlled to be 30 ℃ and 60 ℃ respectively, and after a dry spinning stage of 20cm, the processes of external coagulation bath gelation, continuous water washing, quick drying and the like are sequentially carried out to obtain a hollow fiber membrane with a hydrophilic gradient spongy pore structure with inner density and outer hydrophobicity;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense outer-hydrophobic hydrophilic gradient spongy pore structure obtained in the step (2), dissolving triethoxyfluorosilane in toluene to prepare a hydrophobic modifier solution, wherein the triethoxyfluorosilane is 12.0wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 3h, performing heat treatment at 100 ℃ for 3min, and further cleaning and drying to realize the hydrophobic modification of only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Example 5 a leak-proof humidifying composite hollow fiber membrane, the preparation method thereof comprises:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 20.0wt% of polysulfone powder, 65.0wt% of N-methylpyrrolidone and 15.0wt% of PEG800, specifically, drying polysulfone powder at 60 ℃ in vacuum for 24 hours to remove water, dissolving the polysulfone powder in an N-methylpyrrolidone organic solvent, adding a PEG800 hydrophilic modifier, and mechanically stirring for 32 hours and defoaming for 32 hours to obtain uniform and transparent spinning casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting solution prepared in the step (1) from a spinning nozzle together with core solution at 0.5MPa, wherein the core solution and the external coagulation bath are water, controlling the temperature of the core solution and the temperature of the external coagulation bath to be 30 ℃ and 90 ℃ respectively, and sequentially carrying out the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like after a dry spinning stage of 10cm to obtain a hollow fiber membrane with a hydrophilic gradient spongy pore structure with inner density and outer hydrophobicity;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense and outer-hydrophobic hydrophilic gradient spongy pore structure obtained in the step (2), dissolving tridecafluorooctyl trimethoxysilane in petroleum ether to prepare a hydrophobic modifier solution, wherein the tridecafluorooctyl trimethoxysilane is 1.8wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 1h, performing heat treatment at 90 ℃ for 2min, and further cleaning and drying to realize the hydrophobic modification of only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Example 6A leak-proof humidifying composite hollow fiber membrane, the preparation method thereof comprises:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 14.0wt% of polyethersulfone, 74.0wt% of dimethyl sulfoxide and 12.0wt% of PEG1000, specifically, drying polyethersulfone powder in vacuum at 40 ℃ for 24 hours to remove water, dissolving the polyethersulfone powder in a dimethyl sulfoxide organic solvent, adding a PEG1000 hydrophilic modifier, and mechanically stirring for 6 hours and defoaming for 48 hours to obtain uniform and transparent casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting film liquid prepared in the step (1) from a spinneret together with core liquid at 0.1MPa, wherein the core liquid is water, and the external coagulation bath is a mixed solution of water and dimethyl sulfoxide (volume ratio is 4:1); controlling the temperature of the core liquid and the temperature of the external coagulation bath to be 70 ℃, and sequentially carrying out the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like after a dry spinning stage of 40cm to obtain a hollow fiber membrane with a hydrophilic gradient spongy pore structure with inner density and outer hydrophobicity;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense and outer-hydrophobic hydrophilic gradient spongy pore structure obtained in the step (2), dissolving triethoxyfluorosilane in n-heptane to prepare a hydrophobic modifier solution, wherein the triethoxyfluorosilane is 1.2wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 5h, performing heat treatment at 88 ℃ for 2.5min, and further cleaning and drying to realize the hydrophobic modification of only one side of the inner surface, thereby obtaining the composite leak-proof humidifying hollow fiber membrane for the fuel cell humidifying system.
Example 7 a leak-proof humidifying composite hollow fiber membrane, the method of making comprising:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 22.0wt% of cellulose acetate powder, 70.0wt% of N, N-dimethylformamide and 8.0wt% of PVP-K17, specifically, drying the cellulose acetate powder at 45 ℃ in vacuum for 24 hours to remove water, dissolving the cellulose acetate powder in an N, N-dimethylformamide organic solvent, adding a hydrophilic modifier, mechanically stirring for 24 hours and defoaming for 24 hours to obtain uniform and transparent casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting solution prepared in the step (1) from a spinning nozzle together with core solution at 2.0MPa, wherein the core solution and the external coagulation bath are water, controlling the temperature of the core solution and the external coagulation bath to be 30 ℃ and 70 ℃ respectively, and sequentially performing the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like after a dry spinning stage of 30cm to obtain a hollow fiber membrane with an inner-dense and outer-sparse spongy pore structure;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense outer-hydrophobic hydrophilic gradient spongy pore structure obtained in the step (2), dissolving triethoxyfluorosilane in n-hexane to prepare a hydrophobic modifier solution, wherein the triethoxyfluorosilane is 1.6wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 3h, performing heat treatment at 80 ℃ for 1min, and further cleaning and drying to realize the hydrophobic modification of only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Example 8A leak-proof humidifying composite hollow fiber membrane, the preparation method thereof comprises:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 16.0wt% of polyether modified polysulfone powder, 78.0wt% of N, N-dimethylacetamide and 6.0wt% of PEG400, specifically, drying polyether modified polysulfone powder in vacuum at 55 ℃ for 24 hours to remove water, dissolving the polyether modified polysulfone powder in an N, N-dimethylacetamide organic solvent, adding a PEG400 hydrophilic modifier, mechanically stirring for 12 hours and defoaming for 12 hours to obtain uniform and transparent spinning casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting film liquid prepared in the step (1) from a spinning nozzle together with core liquid at 1.7MPa, wherein the core liquid is water, an external coagulation bath is a mixed solution of water and N, N-dimethylacetamide (volume ratio is 8:1), the temperature of the core liquid and the temperature of the external coagulation bath are controlled to be 40 ℃, and after a dry spinning stage of 50cm, the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like are sequentially carried out to obtain the hollow fiber film with an internal-density external-sparse spongy pore structure;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the hydrophilic gradient spongy pore structure with the inner density and the outer hydrophobicity, dissolving triethoxyfluorosilane in petroleum ether to prepare a hydrophobic modifier solution, wherein the triethoxyfluorosilane is 0.8wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 5h, performing heat treatment at 120 ℃ for 5min, and further cleaning and drying to realize the hydrophobic modification of only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Example 9A leak-proof humidifying composite hollow fiber membrane, the preparation method thereof comprises:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 20.0wt% of sulfonated polyethersulfone powder, 66.0wt% of N-methylpyrrolidone and 14.0wt% of PVP-K60, specifically, drying the sulfonated polyethersulfone powder at 60 ℃ in vacuum for 24 hours to remove water, dissolving the sulfonated polyethersulfone powder in an N-methylpyrrolidone organic solvent, adding a PVP-K30 hydrophilic modifier, mechanically stirring for 72 hours and defoaming for 72 hours to obtain uniform and transparent spinning casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting solution prepared in the step (1) from a spinning nozzle together with core solution at 1.3MPa, wherein the core solution is water, the external coagulation bath is a mixed solution of water and N-methylpyrrolidone (volume ratio is 9:1), the temperature of the core solution and the temperature of the external coagulation bath are controlled to be 90 ℃, and after a dry spinning stage of 20cm, the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like are sequentially carried out to obtain the hollow fiber membrane with an internal-density external-sparse spongy pore structure;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense and outer-hydrophobic hydrophilic gradient spongy pore structure obtained in the step (2), dissolving polydimethylsiloxane in n-heptane to prepare a hydrophobic modifier solution, wherein the polydimethylsiloxane is 0.4wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution, performing heat treatment at 100 ℃ for 2min, and further cleaning and drying to realize the hydrophobic modification of only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Example 10 a leak-proof humidifying composite hollow fiber membrane, the method of making comprising:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 19.0wt% of cellulose acetate powder, 63.0wt% of N, N-dimethylacetamide and 18.0wt% of PVP-K90, specifically, drying the cellulose acetate powder at 50 ℃ in vacuum for 24 hours to remove water, dissolving the cellulose acetate powder in an N, N-dimethylacetamide organic solvent, adding PVP-K90 hydrophilic modifier, mechanically stirring for 48 hours and defoaming for 72 hours to obtain uniform and transparent casting solution for later use;
(2) Immersion precipitation phase transfer method: spinning by using a hollow fiber spinning machine, extruding the spinning casting solution prepared in the step (1) from a spinning nozzle together with core solution at 0.5MPa, wherein the core solution and the external coagulation bath are water, controlling the temperature of the core solution and the temperature of the external coagulation bath to be 30 and 90 ℃, and sequentially performing the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like after a dry spinning stage of 25cm to obtain the hollow fiber membrane with an inner-dense and outer-spongy pore structure;
(3) Modifying by a hydrophobic modifier solution: and (3) packaging the end part of the hollow fiber membrane with the inner-dense and outer-sparse spongy pore structure obtained in the step (2), dissolving 1.2wt% of heptadecafluorodecyl triethoxysilane into dimethylbenzene to prepare a hydrophobic modifier solution, wherein the heptadecafluorodecyl triethoxysilane is 1.2wt% of the hydrophobic modifier solution, flushing the inner surface of the hollow fiber membrane by using the hydrophobic modifier solution for 2h, performing heat treatment for 4min at 90 ℃, and further cleaning and drying to realize hydrophobic modification on only one side of the inner surface, thereby obtaining the leak-proof humidifying composite hollow fiber membrane for the fuel cell humidifying system.
Comparative example 1 a hollow fiber membrane with a hydrophilic gradient spongy pore structure with dense inside and hydrophobic outside, the preparation method is as follows:
(1) Preparing spinning casting film liquid: preparing spinning casting solution according to the proportion of 20.0wt% of cellulose acetate powder, 60.0wt% of N, N-dimethylacetamide and 20.0wt% of PVP-K90, specifically, drying the cellulose acetate powder at 60 ℃ in vacuum for 24 hours to remove water, dissolving the cellulose acetate powder in an N, N-dimethylacetamide organic solvent, adding PVP-K90 hydrophilic modifier, mechanically stirring for 48 hours and defoaming for 72 hours to obtain uniform and transparent spinning casting solution for later use;
(2) Immersion precipitation phase transfer method: and (3) spinning by using a hollow fiber spinning machine, extruding the spinning casting film liquid prepared in the step (1) from a spinneret under the pressure of 1.2MPa, wherein the core liquid is water, the external coagulation bath is a mixed solution of water and N-methylpyrrolidone (volume ratio is 9:1), the temperature of the core liquid and the temperature of the external coagulation bath are controlled to be 50 ℃, and the processes of gelation of the external coagulation bath, continuous water washing, quick drying and the like are sequentially carried out after a dry spinning stage of 25cm, so that the hollow fiber film with the hydrophilic gradient spongy pore structure with internal density and external hydrophobicity is obtained.
Comparative example 2A leakage-proof humidifying composite hollow fiber membrane
Comparative example 2 differs from example 2 in that tridecafluorooctyltrimethoxysilane was 0.05wt% of the hydrophobic modifier solution, and the remainder was the same as in example 2.
Comparative example 3A leakage-proof humidifying composite hollow fiber membrane
Comparative example 3 differs from example 2 in that tridecafluorooctyltrimethoxysilane was 25.0wt% of the hydrophobic modifier solution, and the remainder was the same as in example 2.
Performance detection
Taking the hollow fiber membranes prepared in examples 1-10 and comparative examples 1-3 as experimental objects, performing thickness test on the hydrophilic membrane by using a thickness gauge before modifying the hydrophobic modifier solution, and testing the thickness of the inner hydrophobic layer by using a field emission scanning electron microscope; testing the pore size distribution of the outer surface of the outer hydrophilic layer and the inner surface of the inner hydrophobic layer by using a field emission scanning electron microscope (obtaining a membrane pore size average value through calculation); spreading the hollow fiber membrane on a glass sheet, dripping a water drop with a fixed volume from a syringe of a contact angle tester to enable the water drop to contact the surface of the membrane, slowly lifting the syringe, and recording the water contact angle value of the water drop after the water drop contacts the surface of the membrane stably.
To investigate the feasibility of hollow fiber membranes for humidification of flowing air according to examples and comparative examples, the present application made hollow fiber membranes into a humidification membrane module with air flow channels (hollow fiber membranes were packaged and fixed into a humidifier membrane housing using polyurethane glue or modified acrylate adhesive (AB glue), and were ready to use). In the membrane module, purge air from the compressed air tank can take away water molecules permeated and diffused inside the membrane module for humidification. Parameters of the humid air and the purge air (such as temperature, humidity and flow rate) are both controllable in the system. The system is humidified by an air humidification system, and the humidity and flow of humidification can be regulated and controlled by a valve. The purge air in this application has a temperature of 30deg.C, humidity of 45-52% RH, and flow rate of 2.0X10 -2 g/s; the humidity of the humid air was 100% RH and the flow rate was 2.0X10 -2 g/s. The inlet and outlet temperatures on both sides of the process air can be measured by Pt-Rt Ds thermocouples with an accuracy of 0.2 ℃; the humidity of the inlet and outlet air was measured using a humidity sensor (Aosong AF 3485A) with an accuracy of 2% rh.
Table 1 shows the performance data of hollow fiber membranes prepared in examples 1 to 10 and comparative examples 1 to 3 of the present application
As can be seen from the test results of Table 1, the inner and outer surfaces of the hollow fiber membranes which are not modified by the hydrophobic modifier solution in comparative example 1 are hydrophilic, and the composite hollow fiber membranes prepared in examples 1 to 10 are higher than 120 degrees in contact angle of the inner hydrophobic layer after being modified by the hydrophobic modifier solution, and have an asymmetric structure of the outer hydrophilic layer and the inner hydrophobic layer, so that the humidifying effect is excellent, and the leak-proof humidifying composite hollow fiber membrane with the asymmetric structure of the inner hydrophobic layer and the outer hydrophilic layer is favorable for capturing and penetrating water molecules and escaping water vapor of the fuel cell system, so that the excellent and stable humidifying effect is realized.
Compared with comparative examples 2 and 3, when the concentration of the hydrophobic modifier solution is too low, the prepared composite hollow fiber membrane has smaller hydrophobic layer thickness and poorer hydrophobicity, and is not beneficial to water vapor permeation and separation from the hollow fiber membrane; when the concentration of the hydrophobic modifier solution is too high, the thickness of the hydrophobic layer in the prepared composite hollow fiber membrane is higher, and the too high hydrophobicity is unfavorable for capturing and penetrating water molecules through the hollow fiber membrane; it can be seen that the content of the hydrophobic modifier is controlled to be 0.1-20wt%, and the prepared composite asymmetric hollow fiber membrane has the most excellent performance.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Claims (20)
1. The leak-proof humidifying composite hollow fiber membrane is characterized by comprising an outer hydrophilic layer and an inner hydrophobic layer attached to the inner surface of the outer hydrophilic layer, wherein the outer hydrophilic layer is provided with a spongy pore structure, the pore diameter of the outer surface is changed from large to small, and the thickness of the inner hydrophobic layer of the leak-proof humidifying composite hollow fiber membrane is smaller than that of the outer hydrophilic layer;
the leak-proof humidifying composite hollow fiber membrane is prepared by the following method: firstly, preparing spinning casting solution into a hollow fiber membrane with an inner-dense outer-spongy pore structure by using an immersion precipitation phase transfer wet spinning or dry-wet spinning technology through core solution and external coagulation bath regulation and control, and then modifying the inner surface of the hollow fiber membrane with the inner-dense outer-spongy pore structure by using a hydrophobic modifier solution to prepare a leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer asymmetric structure;
The hydrophobic modifier solution comprises: 0.1-20.0 wt% of hydrophobic modifier and 80-99.9wt% of solvent.
2. The leak-proof humidifying composite hollow fiber membrane of claim 1, wherein the outer hydrophilic layer of the leak-proof humidifying composite hollow fiber membrane has an outer surface pore size of 0.1 to 0.3 μm and the inner hydrophobic layer has a surface pore size of 0.005 to 0.07 μm.
3. The leak-proof humidifying composite hollow fiber membrane of claim 1, wherein the inner hydrophobic layer of the leak-proof humidifying composite hollow fiber membrane has a thickness of 0.5-5.0 μm; the thickness of the outer hydrophilic layer is 0.1-0.3 mm.
4. The leak-proof humidifying composite hollow fiber membrane of claim 1, wherein the contact angle of the inner hydrophobic layer of the leak-proof humidifying composite hollow fiber membrane is greater than 120 °; the contact angle of the outer hydrophilic layer is less than 30 °.
5. The leak-proof humidifying composite hollow fiber membrane of claim 1, wherein the hydrophobic modifier is one or more of polydimethylsiloxane, triethoxysilane, tridecafluorooctyltrimethoxysilane, heptadecafluorodecyltriethoxysilane.
6. The leak-proof humidifying composite hollow fiber membrane of claim 1, wherein the solvent is one or more of n-hexane, n-heptane, toluene, xylene, petroleum ether.
7. The leak-proof humidifying composite hollow fiber membrane of claim 1, wherein the spin casting solution comprises: 14.0 to 24.0 weight percent of hydrophilic polymer, 56.0 to 84.0 weight percent of organic solvent and 2.0 to 20.0 weight percent of hydrophilic modifier.
8. The leak resistant humidifying composite hollow fiber membrane of claim 7, wherein the hydrophilic polymer is one or more of cellulose, polysulfone, polyethersulfone, polyether modified polysulfone, sulfonated polyethersulfone, cellulose acetate.
9. The leak-proof humidifying composite hollow fiber membrane of claim 7, wherein the organic solvent is one or more of dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone.
10. The leak-proof moisturizing composite hollow fiber membrane of claim 7, wherein the hydrophilic modifier is one or more of PEG200, PEG400, PEG800, PEG1000, PEG2000, PVP-K17, PVP-K30, PVP-K60, PVP-K90, polyvinyl alcohol.
11. The leak-proof humidifying composite hollow fiber membrane of claim 1, wherein the core liquid is water and the external coagulation bath is one or more of water, dimethyl sulfoxide, N-dimethylformamide, N-dimethylacetamide, N-methylpyrrolidone.
12. The leak-proof humidifying composite hollow fiber membrane of claim 11, wherein when the external coagulation bath contains an organic solvent, the organic solvent comprises no more than 80vol% of the external coagulation bath.
13. A method of preparing the leak-proof humidifying composite hollow fiber membrane of any one of claims 1-12, comprising: preparing spinning casting solution, preparing a hollow fiber membrane with an inner-dense outer-sparse spongy pore structure by an immersion precipitation phase transfer method, and modifying by a hydrophobic modifier solution to prepare the leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer asymmetric structure.
14. The method for preparing the leak-proof humidifying composite hollow fiber membrane according to claim 13, wherein the preparation of the spinning casting solution is specifically: the hydrophilic polymer solid powder is dried in vacuum at 40-60 ℃ to remove water, then is dissolved in an organic solvent, then is added with a hydrophilic modifier, and is mechanically stirred for 6-72 h and defoamed for 12-72 h to obtain uniform and transparent spinning casting solution, wherein the hydrophilic polymer accounts for 14.0-24.0wt% of the spinning casting solution, the organic solvent accounts for 56.0-84.0wt% of the spinning casting solution, and the hydrophilic modifier accounts for 2.0-20.0wt% of the spinning casting solution.
15. The method for preparing a leak-proof humidifying composite hollow fiber membrane according to claim 14, wherein the hydrophilic polymer solid powder is vacuum-dried at 40-60 ℃ for 24 hours.
16. The method for preparing the leak-proof humidifying composite hollow fiber membrane according to claim 14 or 15, wherein the immersion precipitation phase transfer method for preparing the hollow fiber membrane with an inner-dense outer-spongy pore structure is specifically as follows: extruding the spinning casting film liquid and the core liquid from a spinning nozzle, controlling the temperature of the core liquid and the temperature of an external coagulation bath to be 30-90 ℃, and sequentially carrying out external coagulation bath gelation, continuous water washing and quick drying after a dry spinning stage of 5-50 cm to obtain the hollow fiber membrane with an internal-dense and external-sparse spongy pore structure.
17. The method for preparing the leak-proof humidifying composite hollow fiber membrane according to claim 16, wherein the leak-proof humidifying composite hollow fiber membrane with an inner hydrophobic layer and an outer hydrophilic layer asymmetric structure is prepared by modifying the hydrophobic modifier solution specifically comprises: firstly, packaging a hollow fiber membrane with an inner-dense and outer-spongy pore structure, dissolving a hydrophobic modifier in a solvent to prepare a hydrophobic modifier solution, then flushing the inner surface of the hollow fiber membrane with the inner-dense and outer-spongy pore structure by using the hydrophobic modifier solution for 1-5 h, and then carrying out heat treatment for 1-5 min at the temperature of 80-120 ℃.
18. The method for preparing the leak-proof humidifying composite hollow fiber membrane according to claim 17, wherein the encapsulation treatment is to fix a bundle of hollow fiber membranes with inner-dense outer-spongy pore structures together by using polyurethane glue or modified acrylate adhesive and encapsulate the hollow fiber membranes into an assembly, and after the polyurethane glue or the modified acrylate adhesive is dried, the hollow fiber membranes are cut off by using a cutter to keep the membrane wire ports smooth.
19. Use of a leak-proof humidifying composite hollow fiber membrane according to any one of claims 1 to 12 in a humidification process outside the gas humidification system of a fuel cell.
20. A membrane humidifier, characterized in that the membrane humidifier employs the leak-proof humidifying composite hollow fiber membrane according to any one of claims 1 to 12 as a humidifying membrane.
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