Preparation method of porous gas diffusion film

Abstract

The invention belongs to the technical field of energy conservation and environmental protection, and discloses a preparation method of a porous gas diffusion film, which comprises the following steps: preparing raw materials, uniformly mixing the raw materials, a diluting solvent, a nonionic surfactant and fused salt, and melting to form a precursor solution; the precursor solution is melt-blown through a hot air driving spinning nozzle to form silk fibers, the silk fibers are transversely distributed to form fiber layers by controlling the spinning nozzle to transversely move relative to the spinning direction, a laminated structure formed by laminating at least two fiber layers is subjected to hot pressing to form a film, and a blank is obtained; and after the blank is cooled, molten salt is removed in a water washing mode, and then the blank is wound and cut into the proper size. The porous gas diffusion film prepared by the method has porous structures with different sizes, so that the gas diffusion resistance can be effectively reduced, and the gas can be quickly guided out along the microtube structure by virtue of the macropores; according to the method, the porosity, the aperture range and the roughness of the membrane can be adjusted, and the whole preparation method is relatively simple and low in cost.

Description

Technical Field

[0001] The invention belongs to the technical field of energy conservation and environmental protection, and specifically relates to a method for preparing a porous gas diffusion membrane. Background Art

[0002] Alkaline electrolyzer is a commonly used electrolysis device, widely used in the fields of electrolysis of water to produce hydrogen, etc. The adjacent plates of the device (i.e. the positive and negative plates of an electrolysis unit) are separated by a diaphragm, and the electrodes are located in the small chamber of the electrolyzer. The electrolysis reaction is promoted by the catalyst on the electrode. However, since gas is generated during the reaction, if the gas cannot be discharged in time, the pressure in the flow channel will increase, and it may also pass through the diaphragm to the other side of the diaphragm, and it may also increase the gap between the diaphragm and the catalyst. In order to quickly export the gas generated by the reaction, there is a technology in the prior art that uses the bionic structure of plant vascular bundles to quickly export the gas to the outlet of the electrolysis unit. For example, the invention patent "A zero-gap electrolytic cell with a plant vascular bundle bionic structure", application number: 202410175454.6, discloses a zero-gap electrolytic cell with a plant vascular bundle bionic structure, including a plurality of electrolytic units arranged in series, the electrolytic units are fixed by a compression structure, the electrolytic units include two plates serving as a cathode and an anode respectively, a diaphragm and a sealing structure located between the two plates to separate the two plates, a plant vascular bundle bionic structure with a gas channel is provided in the electrolytic unit, a plurality of reaction channels are provided on the side of the plate facing the diaphragm, the plant vascular bundle bionic structure fills the reaction channel, the plant vascular bundle bionic structure includes a hydrophobic gas channel and an elastic catalytic element provided on the outside of the gas channel, the elastic catalytic element is tightly fitted with the diaphragm without a gap; the gas outlet end of the plant vascular bundle bionic structure extends outside the electrolytic unit of the electrolytic cell, and the gas outlet end extends to the outlet of the electrolytic unit.

[0003] In the above-mentioned prior art, the plant vascular bundle bionic structure is the core structure for realizing rapid gas extraction, and the hydrophobic porous fiber bundle forming a bionic structure similar to the plant vascular bundle is the key component for realizing gas-liquid separation and rapid gas extraction in the structure. However, although there are gas diffusion layers made of hydrophobic materials in the prior art in the field of electrolysis technology, such structures are usually only used to realize gas-liquid separation and gas diffusion inside the electrolysis unit, and the need for directional gas delivery outside the electrolysis unit is not considered. Therefore, its structure and performance cannot meet the requirements of the porous gas diffusion membrane required by the plant vascular bundle bionic structure. How to efficiently and reliably prepare and produce a porous gas diffusion membrane that meets the requirements of the hydrophobic porous fiber bundle has also become a technical problem that needs to be solved in the prior art. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a porous gas diffusion membrane, so as to solve the technical problem in the prior art that a porous gas diffusion membrane meeting the requirements of a hydrophobic porous fiber bundle is difficult to be prepared efficiently and reliably.

[0005] The method for preparing a porous gas diffusion membrane comprises: after preparing the raw materials, evenly mixing the raw materials, a diluting solvent, a non-ionic surfactant and a molten salt, and then melting them to form a precursor solution; driving the precursor solution through a hot air driven spinneret to melt-blow to form silk fibers, and controlling the spinneret to move laterally relative to the spinning direction so that the silk fibers are laterally distributed to form a fiber layer, and a stacked structure formed by stacking at least two layers of fiber layers is sent to a hot pressing molding device for hot pressing to form a film to obtain a blank; after cooling the blank, washing it with water to remove the molten salt, and then winding the blank and cutting it into a suitable size, and the axial direction of the winding is consistent with the extension direction of the silk fibers; the raw material is a polymer material with hydrophobicity and thermoplasticity, and there is a microtubule structure in the porous gas diffusion membrane, and the microtubule structure is in the same direction as the extension direction of the silk fibers and becomes a channel for rapid gas diffusion.

[0006] Preferably, the raw material includes one or more of polyphenylene sulfide, polysulfone and polytetrafluoroethylene.

[0007] Preferably, the raw material is polyphenylene sulfide, the molecular weight of polyphenylene sulfide should be no less than 100,000 Daltons, and the molecular weight distribution coefficient should be between 1.5 and 3.0.

[0008] Preferably, the precursor solution comprises the following components, measured by weight: 70 to 90 parts of polyphenylene sulfide, 27 to 9 parts of diluent, and 3 to 1 part of nonionic surfactant.

[0009] Preferably, polyphenylene sulfide, a diluent solvent and a nonionic surfactant form a polyphenylene sulfide solution, and the mass ratio of the molten salt to the polyphenylene sulfide solution is in the range of 1:3-1.

[0010] Preferably, the molten salt adopts a ternary NaCl-KCl-ZnCl2 eutectic salt, wherein the molar ratio of NaCl:KCl:ZnCl2 ranges from 1 to 5:1:1.

[0011] Preferably, among the spinning process parameters, the spinning temperature is 250-350° C., the spinning pressure is 0.1-0.5 MPa, and the single hole diameter of the spinneret is 0.1 mm-3.0 mm.

[0012] Preferably, the silk fibers of two adjacent fiber layers are staggered and stacked, the gaps between the silk fibers of the same fiber layer are smaller than the diameters of the silk fibers of the adjacent fiber layer, and the silk fibers of the adjacent fiber layer are located in the gaps between the silk fibers of the current fiber layer.

[0013] Preferably, the temperature of the film pressing is controlled in the range of 300-330° C., and the pressure is controlled in the range of 5-7 MPa; the gaps between the silk fibers form the microtube structure in the blank after hot pressing film forming.

[0014] Preferably, the water washing temperature ranges from 80 to 90° C. The water washing dissolves and removes the crystal grains formed by condensation of the molten salt on each silk fiber, forming micropores or mesopores consistent with the grain size.

[0015] The present invention has the following advantages: a large number of pores exist in the porous gas diffusion membrane prepared by the present invention, which are divided into mesopores with a pore size of less than 2nm, mesopores with a pore size of 2 to 50nm, and macropores with a pore size of more than 50nm according to their sizes, and the porosity of the blank is more than 60%. This porous structure effectively reduces the gas diffusion resistance, and the macropores, i.e., microtube structures with an inner diameter greater than 50nm, facilitate the rapid extraction of gas along the microtube structures. By adjusting the composition of the melt, the present method can adjust the porosity, pore size range and roughness of the membrane, and the preparation method is relatively simple as a whole and has low cost.

[0016] The raw material contains only one material, polyphenylene sulfide, and the strength, stability and uniformity of the membrane are relatively high. Molten salt is added to the precursor, and the molten salt is used as a uniform and efficient heat transfer medium to reduce the energy consumption of the heating process. Due to the use of low-melting-point molten salts such as ternary NaCl-KCl-ZnCl2 eutectic salt, controlling the cooling conditions can conveniently refine the condensed grains of the molten salt, which helps to improve the porosity and pore size range of the membrane, further increase the roughness of the membrane surface, and enhance the hydrophobicity and gas diffusion capacity of polyphenylene sulfide. The use of molten salt condensation to form small holes and mesopores on the silk fibers, and then removing the molten salt by washing with water is not only simple and convenient, but the molten salt can also be recycled, with low cost and no pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a flow chart of a method for preparing a porous gas diffusion membrane.

[0018] Figure 2 It is a schematic diagram of the formation of silk fibers into blanks during the process from spinning to washing in the present invention. DETAILED DESCRIPTION

[0019] The specific implementation modes of the present invention will be further explained in detail below by describing the embodiments with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0020] like Figure 1-Figure 2 As shown, the present invention provides a method for preparing a porous gas diffusion membrane, comprising the following steps.

[0021] Step 1: Prepare raw materials.

[0022] This step prepares the raw materials for making porous gas diffusion membranes. The raw materials are polymer materials with hydrophobicity and thermoplasticity, such as polyphenylene sulfide, polysulfone, polytetrafluoroethylene, etc. The raw materials can be two or more polymer materials that meet the hydrophobicity and thermoplasticity requirements, but using the same polymer material can better ensure the strength, stability and uniformity of the porous gas diffusion membrane. Taking polyphenylene sulfide (PPS) as a raw material as an example, the molecular weight of polyphenylene sulfide should not be less than 100,000 Daltons, and the molecular weight distribution coefficient should be between 1.5 and 3.0 to ensure material strength and processing performance; and the polyphenylene sulfide should be sliced ​​in advance to facilitate subsequent melting.

[0023] Step 2: Mix and melt.

[0024] The sliced ​​raw material (such as polyphenylene sulfide material) is transported to the material tank, mixed evenly with the diluent solvent, non-ionic surfactant and molten salt, and then melted to form a precursor solution, wherein polyphenylene sulfide, diluent solvent and non-ionic surfactant constitute a polyphenylene sulfide solution. In terms of mass fractions, the polyphenylene sulfide solution includes the following components: 70 to 90 parts of polyphenylene sulfide, 27 to 9 parts of diluent solvent, and 3 to 1 part of non-ionic surfactant. Among them, the diluent solvent can dissolve the raw material after heating to form a uniform casting solution. In this embodiment, the diluent solvent includes one or more of diphenyl ether, diphenyl ketone, caprolactam and diphenyl sulfone; the non-ionic surfactant includes polyethylene glycol, long-chain fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, fatty acid polyoxyethylene ester, polyoxyethylene alkylamine, polyoxyethylene alkylamide and polyether nonionic surfactant.

[0025] In the precursor solution, the mass ratio of the molten salt and the polyphenylene sulfide solution is in the range of 1:3 to 1. By adjusting the mass ratio range, the strength, pore size and porosity of the resulting product, the porous gas diffusion membrane, can be controlled. Among them, the molten salt is a soluble salt soluble in water with a melting point lower than the spinning temperature. The molten salt can be a single salt or a mixture of salts. In this embodiment, the molten salt uses a ternary NaCl-KCl-ZnCl2 eutectic salt, wherein the molar ratio of NaCl:KCl:ZnCl2 ranges from 1 to 5:1:1, and the optimal molar ratio is 3:1:1.

[0026] Molten salt is added to the precursor, and the molten salt acts as a uniform and efficient heat transfer medium, reducing the energy consumption of the heating process. Since low-melting-point molten salts such as ternary NaCl-KCl-ZnCl2 eutectic salts are used, controlling the cooling conditions can conveniently refine the condensed grains of the molten salt, which helps to improve the porosity and pore size range of the membrane, further increase the roughness of the membrane surface, and enhance the hydrophobicity and gas diffusion capacity of polyphenylene sulfide.

[0027] Step 3: Spinning.

[0028] The precursor solution is filtered and transported to a spinneret, where hot air drives the spinneret to melt-blown to form silk fibers. The spinneret is controlled to move laterally relative to the spinning direction so that the silk fibers are laterally distributed to form a fiber layer with gaps between adjacent silk fibers. The fiber layer is at least two layers, generally two to three layers.

[0029] Among the spinning process parameters, the spinning temperature is 250-350°C, the spinning pressure is 0.1-0.5MPa, and the diameter of the single hole of the spinneret is 0.1mm-3.0mm; the wire diameter can be regulated by controlling the spinning process parameters. In this embodiment, the appropriate single hole diameter of the spinneret is selected according to actual needs (such as wire diameter requirements), the optimal spinning temperature is 310°C, and the optimal spinning pressure is 0.2Mpa. On the other hand, the number of holes of the spinneret can also be customized according to cost and efficiency needs, such as a single hole, 3 holes or 6 holes.

[0030] During spinning, the gap size and lateral distribution density between the silk fibers can be regulated by controlling the lateral movement speed of the spinneret relative to the spinning direction; and the silk fibers of the upper and lower adjacent fiber layers are staggered, that is, the gap size between the silk fibers of the same fiber layer is smaller than the wire diameter of the silk fibers of the adjacent fiber layer, and the silk fibers of the adjacent fiber layer are located in the gaps between the silk fibers of the current fiber layer.

[0031] Step 4: Lamination.

[0032] The laminated structure formed by stacking at least two fiber layers obtained by spinning is sent to a hot pressing molding device, and the fiber layer is hot pressed into a film after being heated to the hot pressing temperature. The film pressing temperature is controlled in the range of 300-330°C, and the pressure is controlled in the range of 5-7MPa. The hot pressing process achieves adhesion between each fiber layer without destroying the fiber layer structure to form a porous gas diffusion membrane blank. The gaps between the silk fibers form a rich microtubule structure in the blank after hot pressing, and the microtubule structure is in the same direction as the extension direction of the silk fibers and becomes a channel for rapid gas diffusion.

[0033] Step 5: Wash with water.

[0034] After the blank is cooled, the molten salt is removed by washing with water, and the washing temperature range is 80-90°C. During cooling, controlling the cooling temperature, cooling rate and cooling time can control the grain size formed by the cooling of the molten salt, and then the grains formed by the condensation of the molten salt on each silk fiber are removed by washing with water, so that micropores or mesopores consistent with the grain size are formed on the silk fiber. After that, the molten salt is removed by washing with water, which is not only simple and convenient, but also the molten salt can be recycled, with low cost and no pollution.

[0035] Step 6: Winding and cutting.

[0036] Finally, as needed, the blank is wound and cut into a suitable size to complete the preparation of the porous gas diffusion membrane. The plant vascular bundle bionic structure also includes an elastic catalytic element, so the blank obtained by this method can be wound separately to form a gas channel and then set in the elastic catalytic element, or it can be first attached to the surface of the elastic catalytic element to form a layered structure and then wound together to form a plant vascular bundle bionic structure. Regardless of the winding method, the axial direction of the winding is consistent with the extension direction of the silk fiber. The cutting is based on the length of the reaction flow channel. The structure formed after winding is cut along the length direction.

[0037] The specific embodiments of this scheme are as follows.

[0038] Example 1.

[0039] Step 1. Raw material preparation: slice the polyphenylene sulfide for later use.

[0040] Step 2, mixed melting: the sliced ​​polyphenylene sulfide material is transported to a material tank, mixed evenly with a diluent solvent, a non-ionic surfactant and a molten salt, and then melted to form a precursor solution, wherein polyphenylene sulfide, a diluent solvent and a non-ionic surfactant constitute a polyphenylene sulfide solution; the polyphenylene sulfide solution includes the following components by mass: 70 parts of polyphenylene sulfide, 27 parts of a diluent solvent, and 3 parts of a non-ionic surfactant; the mass ratio of the molten salt to the polyphenylene sulfide solution is 1:3, and the molten salt adopts a ternary NaCl-KCl-ZnCl2 eutectic salt, wherein the molar ratio of NaCl:KCl:ZnCl2 is 1:1:1.

[0041] Step 3, spinning: the precursor solution is filtered and transported into a spinning box, a single-hole spinneret is used, hot air is used to drive the spinneret to melt-spray to form silk fibers, and the spinneret is controlled to move laterally relative to the spinning direction so that the silk fibers are distributed laterally to form a fiber layer, and there are gaps between adjacent silk fibers; the fiber layer is two layers. Among the spinning process parameters, the spinning temperature is 250°C, the spinning pressure is 0.1Mpa, and the single hole diameter of the spinneret is 0.1mm.

[0042] Step 4: Film pressing: The laminated structure formed by stacking two fiber layers is sent to the hot pressing molding equipment. After being heated to the hot pressing temperature, the fiber layers are hot pressed into a film. The film pressing temperature is controlled at about 300°C and the pressure is controlled at 5MPa. Through short-time hot pressing, the fiber layers are adhered to each other to form a porous gas diffusion membrane blank.

[0043] Step 5: Water washing: After cooling the blank, remove the molten salt by water washing at a temperature of 90°C.

[0044] Step 6: Winding and cutting: Finally, the blank is wound and cut into appropriate size as needed.

[0045] Example 2.

[0046] It is basically the same as Example 1, except that: in step 2, the polyphenylene sulfide solution includes the following components: 80 parts of polyphenylene sulfide, 18 parts of diluent, and 2 parts of non-ionic surfactant; the mass ratio of molten salt and polyphenylene sulfide solution is 1:2; in the ternary NaCl-KCl-ZnCl2 eutectic salt, the molar ratio of NaCl:KCl:ZnCl2 is 3:1:1, and the melting point of the ternary NaCl-KCl-ZnCl2 eutectic salt of the above molar ratio is reduced to about 210°C. In the spinning process parameters of step 3, the spinning temperature is 310°C, the spinning pressure is 0.2MPa, and the single hole diameter of the spinneret is 1mm. In step 4, the temperature of the film pressing is controlled at about 310°C and the pressure is controlled at 6MPa. In step 5, the water washing temperature is 85°C.

[0047] Example 3.

[0048] It is basically the same as Example 1, except that: in step 2, the polyphenylene sulfide solution includes the following components: 90 parts of polyphenylene sulfide, 9 parts of diluent, and 1 part of non-ionic surfactant; the mass ratio of molten salt and polyphenylene sulfide solution is 1:1; in the ternary NaCl-KCl-ZnCl2 eutectic salt, the molar ratio of NaCl:KCl:ZnCl2 is 5:1:1. In the spinning process parameters of step 3, the spinning temperature is 350°C, the spinning pressure is 0.5MPa, and the single hole diameter of the spinneret is 3.0mm. In step 4, the temperature of the film is controlled at about 330°C, and the pressure is controlled at 7MPa. In step 5, the water washing temperature is 80°C.

[0049] The porous gas diffusion membrane obtained by the above embodiment has a large number of pores, which are divided into mesopores with a pore size of less than 2nm, mesopores with a pore size of 2-50nm and macropores with a pore size of more than 50nm, and the porosity of the blank is more than 60%. This porous structure effectively reduces the gas diffusion resistance, and the macropores, i.e., microtube structures with an inner diameter of more than 50nm, facilitate the rapid discharge of gas along the microtube structure.

[0050] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the inventive concept and technical solution of the present invention, or the inventive concept and technical solution are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a porous gas diffusion membrane, characterized in that: include: After the raw materials are prepared, the raw materials, diluent solvent, non-ionic surfactant and molten salt are mixed evenly and then melted to form a precursor solution; The precursor solution is melt-blown through a hot air-driven spinneret to form silk fibers, and the silk fibers are distributed laterally to form fiber layers by controlling the lateral movement of the spinneret relative to the spinning direction. The laminated structure formed by at least two fiber layers is sent to a hot pressing molding device for hot pressing into a film to obtain a blank; after the blank is cooled, it is washed with water to remove the molten salt, and then the blank is wound and cut into a suitable size, and the axial direction of the winding is consistent with the extension direction of the silk fibers; the raw material is a hydrophobic and thermoplastic polymer material, and a microtubule structure exists in the porous gas diffusion membrane, and the microtubule structure is in the same direction as the extension direction of the silk fibers and becomes a channel for rapid gas diffusion.

2. The method for preparing a porous gas diffusion membrane according to claim 1, characterized in that: The raw materials include one or more of polyphenylene sulfide, polysulfone and polytetrafluoroethylene.

3. The method for preparing a porous gas diffusion membrane according to claim 1, characterized in that: The raw material is polyphenylene sulfide, the molecular weight of the polyphenylene sulfide should not be less than 100,000 Daltons, and the molecular weight distribution coefficient should be between 1.5 and 3.

0.

4. The method for preparing a porous gas diffusion membrane according to claim 3, characterized in that: The precursor solution includes the following components by weight: 70 to 90 parts of polyphenylene sulfide, 27 to 9 parts of a diluent, and 3 to 1 part of a nonionic surfactant.

5. The method for preparing a porous gas diffusion membrane according to claim 4, characterized in that: Polyphenylene sulfide, diluent solvent and non-ionic surfactant constitute a polyphenylene sulfide solution, and the mass ratio of molten salt to the polyphenylene sulfide solution is in the range of 1:3-1.

6. The method for preparing a porous gas diffusion membrane according to claim 1, characterized in that: The molten salt adopts a ternary NaCl-KCl-ZnCl2 eutectic salt, wherein the molar ratio of NaCl:KCl:ZnCl2 ranges from 1 to 5:1:

1.

7. The method for preparing a porous gas diffusion membrane according to claim 1, characterized in that: Among the spinning process parameters, the spinning temperature is 250-350° C., the spinning pressure is 0.1-0.5 MPa, and the single hole diameter of the spinneret is 0.1 mm-3.0 mm.

8. The method for preparing a porous gas diffusion membrane according to claim 1, characterized in that: The silk fibers of the upper and lower adjacent fiber layers are staggered and stacked, the gaps between the silk fibers of the same fiber layer are smaller than the diameters of the silk fibers of the adjacent fiber layer, and the silk fibers of the adjacent fiber layer are located in the gaps between the silk fibers of the current fiber layer.

9. The method for preparing a porous gas diffusion membrane according to claim 1, characterized in that: The temperature of the film pressing is controlled within the range of 300-330° C., and the pressure is controlled within the range of 5-7 MPa; the gaps between the silk fibers form a micro-tube structure in the blank after the hot pressing film forming.

10. The method for preparing a porous gas diffusion membrane according to claim 1, characterized in that: The water washing temperature ranges from 80 to 90° C. The water washing dissolves and removes the crystal grains formed by condensation of the molten salt on each silk fiber, forming micropores or mesopores consistent with the grain size.

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