Alkali-resistant super-hydrophobic PTFE hollow fiber membrane and modification method of membrane module

Abstract

The invention belongs to the technical field of water electrolysis hydrogen production, and relates to a modification method of an alkali-resistant super-hydrophobic PTFE hollow fiber membrane and a membrane component, the method adopts the main process of alkali treatment hydroxylation, fluorosilane coating growth and heating curing, and a hydrophobic layer is grown on the surfaces of the PTFE hollow fiber membrane and the component thereof, so that super-hydrophobic modification is realized. A perfluorosilane hydrophobic layer and a rich long-chain CF2 structure are uniformly and densely distributed on the surface of the modified membrane, so that the surface energy of the PTFE membrane is remarkably reduced, and meanwhile, the surface roughness is improved, so that the hydrophobicity is improved; due to the anti-infiltration performance of the coating, seawater and a concentrated alkali solution are not easy to attach to the surface of the membrane, so that the service life of the membrane component in the application of supplying water to the concentrated alkali solution from the seawater is remarkably prolonged; the coating uniformly grows on a separation layer of the PTFE hollow fiber membrane, and meanwhile, membrane holes are fully reserved, so that the flux of water vapor is maintained.

Description

Technical Field

[0001] This invention belongs to the field of water electrolysis hydrogen production technology, and relates to a method for modifying hollow fiber membranes, particularly a method for modifying alkali-resistant superhydrophobic PTFE hollow fiber membranes and membrane modules. Background Technology

[0002] Currently, the hydrogen production industry through water electrolysis has developed rapidly, especially alkaline water electrolysis technology, for which mature commercial production models have been established for electrolyzers, electrodes, and catalyst materials. However, electricity and water resources remain the core cost components of this field. Abundant wind and solar energy resources at sea provide ample electricity, while seawater provides a continuous supply of water for electrolysis. Therefore, the use of desalinated seawater for hydrogen production through water electrolysis has received considerable attention in recent years.

[0003] Membrane distillation for seawater desalination not only produces high-purity desalinated water, but the preheating process also allows for the recycling of heat generated during electrolysis, thus achieving efficient energy utilization and reducing production costs. Therefore, seawater desalination electrolysis technology has received extensive research attention in recent years. Alicia KJAn et al. (Muhammad Usman Farid, Jehad A. Kharraz, Samriddhi Sharma, et al. Technological advancements in waterheating approaches for membrane distillation desalination process: From bulk to localized heating[J]. Desalination, 2024, 574(6): 117235.) have summarized and discussed the current development status of energy coupling technologies such as photovoltaic, geothermal, and electrolytic heat generation with membrane distillation, proving the economic feasibility of this technology; Wen Zhang et al. (Xiaonan Xu, Zhijie Zhao, Chunfeng Song, et al. Seawater Membrane Distillation Coupled with Alkaline Water Electrolysis for Hydrogen Production: Parameter Influence and Techno-Economic Analysis[J]. Membranes, 2025, 15(2): 60.) The integrated process of membrane distillation (MD) and water electrolysis was optimized using a mathematical model. Factors affecting the water production to water consumption ratio, including electrolyzer power and seawater temperature, were identified. The integrated technology was also evaluated technically and economically, which promoted its industrial application.

[0004] In current mature seawater desalination electrolysis technologies, desalination and electrolysis are completely separate processes. However, coupling them into a unified unit—that is, arranging hollow fiber membranes for seawater desalination in an alkaline water electrolyzer—can significantly reduce equipment costs while effectively minimizing heat loss during transmission. PTFE's low surface energy and chemical stability make it one of the best materials for manufacturing membrane distillation modules. While PTFE has strong hydrophobic properties, prolonged exposure to high temperatures and a highly alkaline environment in an alkaline water electrolyzer can gradually decrease its hydrophobicity, thus shortening its lifespan.

[0005] Therefore, it is essential to develop an effective method for hydrophobic modification of PTFE hollow fiber membranes and membrane modules to improve their hydrophobicity, service life and separation performance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a modification method for alkali-resistant superhydrophobic PTFE hollow fiber membranes and membrane modules. By constructing a stable perfluorosilane hydrophobic layer, the hydrophobicity, alkali resistance and service life of the membrane material are synergistically improved, while ensuring its water vapor flux, so as to meet the application requirements of integrated seawater desalination and alkaline water electrolysis hydrogen production technology.

[0007] The technical problem solved by this invention is achieved through the following technical solution: A method for modifying alkali-resistant superhydrophobic PTFE hollow fiber membranes, characterized by comprising the following steps: Step 1: Place the PTFE hollow fiber membrane in an organic solvent and vibrate or sonicate it to completely impregnate it; Step 2: The PTFE hollow fiber membrane obtained in Step 1 is placed in a hydroxylation solution for heat treatment to obtain a PTFE hollow fiber membrane with hydroxyl groups distributed on its surface. Step 3: Rinse and soak the PTFE hollow fiber membrane with hydroxyl groups distributed on its surface obtained in Step 2 with deionized water, and dry it at 30-80℃ for 1-8 hours; Step 4: Prepare a fluorosilane modifier solution using an organic solvent. Fill the PTFE hollow fiber membrane obtained in Step 3 with the fluorosilane modifier solution and tie both ends of the PTFE hollow fiber membrane tightly. Treat it at 20-80 ℃ for 30-150 seconds, then release the fluorosilane modifier from the PTFE hollow fiber membrane. Place the PTFE hollow fiber membrane in an oven at 20-80 ℃ and heat it for 2-8 hours. Then rinse it with deionized water and dry it at 30-60 ℃ for 2-24 hours to form a perfluorosilane hydrophobic layer on the PTFE hollow fiber membrane, thereby forming an alkali-resistant superhydrophobic PTFE hollow fiber membrane.

[0008] Furthermore, the organic reagent includes one or more of methanol solution, ethanol solution, isopropanol solution, and butanol solution.

[0009] Furthermore, the hydroxylation solution is an aqueous solution containing a strong base and a cationic surfactant. The strong base is sodium hydroxide, potassium hydroxide, or calcium hydroxide, and the surfactant is one or more of dodecyl dimethyl benzyl ammonium chloride, dodecyl trimethyl ammonium chloride (bromide), hexadecyl trimethyl ammonium chloride (bromide), octadecyl trimethyl ammonium chloride (bromide), and bis(dodecyl dimethyl ammonium chloride).

[0010] Moreover, the oscillation or ultrasound described in step 1 is performed at 20-90°C for 2-24 hours.

[0011] Furthermore, in step 2, the concentration ratio of the hydroxylation solution is 10-50 wt% strong base and 2-20 wt% cationic surfactant; the heat treatment is carried out at 50-90°C for 4-24 hours.

[0012] Furthermore, the fluorosilane modifier mentioned in step 4 includes one or more of heptadecafluorodecyltrimethoxysilane, perfluorodecyltrichlorosilane, perfluorododecyltrichlorosilane, perfluorooctyltriethoxysilane, octadecyltrichlorosilane, trichlorododecylsilane, and octyltrichlorosilane. The organic solvent used in the fluorosilane modifier solution includes one or more of methanol, ethanol, isopropanol, and butanol, with a solution concentration of 10-50 wt%.

[0013] A method for modifying an alkali-resistant superhydrophobic PTFE hollow fiber membrane module, characterized by comprising the following steps: Step 1: First, inject organic solvent into the PTFE hollow fiber membrane module through the tube inlet and shake or let it stand to wet it; Step 2: Prepare a hydroxylation solution, inject the hydroxylation solution into the tube of the PTFE hollow fiber membrane module obtained in Step 1, and place the PTFE hollow fiber membrane module in an oven for heat treatment to obtain a PTFE hollow fiber membrane module with hydroxyl groups distributed on its surface. Step 3: The PTFE hollow fiber membrane module with hydroxyl groups distributed on its surface obtained in Step 2 is rinsed and soaked with deionized water using a peristaltic pump, and then dried by blowing in an air stream. Step 4: Prepare a fluorosilane modifier solution using an organic solvent, heat the fluorosilane modifier solution, and then, under the impetus of a peristaltic pump, make it flow evenly through the PTFE hollow fiber membrane module tube with hydroxyl groups distributed on its surface obtained in Step 3. Place the PTFE hollow fiber membrane module with hydroxyl groups distributed on its surface in an oven for heating to form a perfluorosilane superhydrophobic layer. Then, rinse with deionized water and blow in air to dry, to obtain the modified PTFE hollow fiber membrane module.

[0014] Furthermore, the organic reagents include one or more of methanol solution, ethanol solution, isopropanol solution, and butanol solution.

[0015] Moreover, the oscillation or resting described in step 1 is carried out at 20-90°C for 12-48 hours.

[0016] Furthermore, the hydroxylation solution is an aqueous solution containing a strong base and a cationic surfactant. The strong base is selected from sodium hydroxide, potassium hydroxide, or calcium hydroxide, and the surfactant is one or more of dodecyl dimethyl benzyl ammonium chloride, dodecyl trimethyl ammonium chloride (bromide), hexadecyl trimethyl ammonium chloride (bromide), octadecyl trimethyl ammonium chloride (bromide), and bis(dodecyl dimethyl ammonium chloride).

[0017] Furthermore, in step 2, the concentration ratio of the hydroxylation solution is 10-50 wt% strong base and 2-20 wt% cationic surfactant, and the heat treatment is carried out at 50-90°C for 4-24 hours.

[0018] Furthermore, the peristaltic pump flow rate in step 3 is set to 10-100 mL / min, the rinsing and soaking with deionized water is carried out at 20-60℃ for 4-24 hours, and the temperature and flow rate of the blown-in dry air flow are 20-80℃ and 10-100 mL / min, respectively.

[0019] Furthermore, the fluorosilane modifier mentioned in step 4 includes one or more of heptadecafluorodecyltrimethoxysilane, perfluorodecyltrichlorosilane, perfluorododecyltrichlorosilane, perfluorooctyltriethoxysilane, octadecyltrichlorosilane, trichlorododecylsilane, and octyltrichlorosilane. The organic solvent used in the fluorosilane modifier solution includes one or more of methanol, ethanol, isopropanol, and butanol, with a solution concentration of 10-50 wt%. The solution is heated at 30-80 ℃, the peristaltic pump flow rate is set to 10-100 mL / min, the oven heating is carried out at 20-80 ℃ for 2-8 hours, the rinsing and soaking with deionized water is carried out at 20-60 ℃ for 4-24 hours, and the temperature and flow rate of the blown dry air are 20-80 ℃ and 10-100 mL / min, respectively.

[0020] The advantages and positive effects of this invention are: This method for modifying alkali-resistant superhydrophobic PTFE hollow fiber membranes and membrane modules involves treating the PTFE hollow fiber membrane with a hydroxylation solution composed of concentrated alkali and surfactants, thereby generating OH active sites on its surface that can bind. Based on this, a perfluorosilane hydrophobic layer is grown on the membrane surface. The resulting hydrophobic layer has stable loading and provides uniform thickness and chemical stability throughout the membrane.

[0021] The perfluorosilane water transport layer loaded on the surface of the PTFE hollow fiber membrane has a strongly hydrophobic CF2 long chain, which can significantly reduce the surface energy of the PTFE hollow fiber membrane and increase the surface roughness, thereby improving hydrophobicity. The hydrophilic angle of the membrane surface increases from 112.5° to 154.2°. The anti-wetting properties of the coating make the membrane surface less susceptible to adhesion by seawater and concentrated alkaline solutions, thus significantly increasing the lifespan of the membrane module in seawater to concentrated alkaline solution water supply applications. After 7 days of high-temperature strong alkaline solution treatment, it still has a contact angle of 127.9°.

[0022] Fluorosilane modifiers can be injected through membrane pores and flow through the macropores of the support layer to accumulate on the surface, so that the hydrophobic layer grows uniformly on the "separation layer" of the PTFE hollow fiber membrane, while the membrane pores are fully preserved, thus maintaining the water vapor flux.

[0023] For membrane modules, the modification solution can be added through the tube inlet, making the modification method simple and efficient. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the modification process of a single PTFE hollow fiber membrane according to the present invention; Figure 2 This is a schematic diagram of the modification process for the PTFE hollow fiber membrane module of the present invention; Figure 3 The diagram below shows the arrangement of membrane fibers in the PTFE hollow fiber membrane module of the present invention. Figure 4 This is a schematic diagram of the polymerization mechanism of PFDTS on the surface of hydroxylated PTFE hollow fiber membrane according to the present invention; Figure 5 SEM images of the original inner / outer surface and the hydrophobic layer on the modified outer surface of the PTFE hollow fiber membrane of this invention; Figure 6 This is an image showing the elemental distribution on the outer surface of the modified PTFE hollow fiber membrane of this invention. Figure 7 In the figure, a is the infrared spectrum image of the outer surface of the PTFE hollow fiber membrane before and after modification, b is the XPS spectrum of Si 2p of the modified membrane, and c and d are the XPS spectra of O 1s of the original membrane and the modified membrane, respectively. Figure 8 Figure a shows the O element distribution after the alkali stability test of the original membrane of the present invention; Figure b shows the O element distribution after the alkali stability test of the modified membrane of the present invention; Figure c shows the schematic diagram of the content of elements C, F and O; Figure d shows the hydrophilic angle test results, where the horizontal axis represents the membrane type and state, and the vertical axis represents the hydrophilic angle; Figure e shows the dynamic hydrophilic angle test results of the modified membrane. Figure 9 This is a schematic diagram of the flux testing process for the modified membrane module of the present invention; Figure 10 The diagram shows the flux test results of the modified membrane module of the present invention. Figure a shows the curve of temperature affecting flux, where the horizontal axis represents the seawater feed temperature and the vertical axis represents the water vapor flux; Figure b shows the curve of flow rate affecting flux, where the horizontal axis represents the seawater feed flow rate and the vertical axis represents the water vapor flux. Figure 11 This is a schematic diagram of the modified PTFE hollow fiber membrane of the present invention, as well as scanning electron microscope images of its inner and outer surfaces.

[0025] Explanation of reference numerals in the attached figures 1-Membrane distillation assembly, 2-Peristaltic pump, 3-Membrane fiber, 4-Membrane shell, 5-Chloride ion selective electrode, 6-Thermometer, 7-PTFE hollow fiber membrane assembly, 8-Flow meter, 9-Seawater thermostat, 10-Balance, 11-Alkali thermostat. Detailed Implementation

[0026] The embodiments of the present invention will be further described in detail below with reference to the accompanying drawings: In this invention, the PTFE hollow fiber membrane is first treated with a hydroxylation solution to achieve surface hydroxylation, and then a hydrophobic layer is formed by instilling a fluorosilane modifier and curing it by heating. Fluorosilane modifiers are commonly used hydrophobic modifiers; the large number of fluorine groups on their branches gives them extremely low surface energy. Simultaneously, the nano-recessed structure formed by the flattened branches also increases the roughness of the originally smooth PTFE hollow fiber membrane surface, making it difficult for water droplets to remain and wet, thus giving the formed hydrophobic layer excellent hydrophobicity. Furthermore, as... Figure 10 As shown, this invention employs a PTFE hollow fiber membrane structure of "large-pore support + small-pore separation," namely, a thick support layer with large pores inside and a thin separation layer with small pores outside. The overall membrane porosity reaches over 80%, maintaining high water vapor flux while exhibiting excellent separation performance. The modification process involves injecting fluorosilane modifiers into the membrane, thereby increasing the modification on the side closer to seawater. This reduces seawater wetting while maintaining the pore structure of the separation layer, thus preserving mass transfer flux.

[0027] This invention provides a method for modifying alkali-resistant superhydrophobic PTFE hollow fiber membranes and membrane modules, the innovation of which lies in the following steps: Step 1, Pretreatment of PTFE hollow fiber membrane: The PTFE hollow fiber membrane is first placed in an organic solvent and vibrated or sonicated to completely impregnate it. Then, a syringe is used to fill the hollow fiber membrane with a hydroxylation modification solution. Step 2, hydroxylation of PTFE hollow fiber membrane: The PTFE hollow fiber membrane obtained in step 1 is placed in a hydroxylation solution and heated. Under the action of the hydroxylation solution, hydroxyl groups are fully grown on the inner surface of the hollow fiber membrane, thus obtaining a PTFE hollow fiber membrane with hydroxyl groups distributed on the surface. Then, the obtained PTFE hollow fiber membrane is thoroughly rinsed and soaked with deionized water. Step 3, hydrophobic modification of PTFE hollow fiber membrane: A fluorosilane modifier solution is prepared. One end of the PTFE hollow fiber membrane obtained in step 2 is tied tightly, and then the solution is filled into the hollow fiber membrane. The other end is also tied tightly. Then, it is placed in an oven and heated for a short time to promote the surface polymerization of fluorosilane, thereby forming a superhydrophobic layer. The resulting hollow fiber membrane is then thoroughly cleaned and dried to obtain the product membrane, which can be used for performance testing and chemical characterization.

[0028] This invention provides a method for modifying alkali-resistant superhydrophobic PTFE hollow fiber membrane modules, the innovation of which lies in: specifically including as follows Figure 2 The following steps are shown: Step 1, Pretreatment of PTFE hollow fiber membrane module 7: The PTFE hollow fiber membrane module is first filled with organic solvent from the tube inlet, and then continuously shaken and allowed to stand to wet it. Step 2, hydroxylation of PTFE hollow fiber membrane module: A hydroxylation solution was prepared and injected into the tube of the PTFE hollow fiber membrane module obtained in step 1. The module was then placed in an oven for heat treatment to obtain a PTFE hollow fiber membrane with hydroxyl groups distributed on its surface. Subsequently, the obtained PTFE hollow fiber membrane module was rinsed and soaked with deionized water using a peristaltic pump 2 and dried by blowing in an air stream. Step 3, hydrophobic modification of PTFE hollow fiber membrane modules: A fluorosilane modifier solution was prepared and heated. Then, a peristaltic pump was used to push it to flow evenly through the PTFE hollow fiber membrane module tube obtained in step 3. The module was then placed in an oven and heated to form a superhydrophobic layer. After rinsing with deionized water, the module was dried by blowing in an air stream to obtain the modified PTFE hollow fiber membrane module.

[0029] Example 1 A hydrophobic layer of PFDTS (1H,1H,2H,2H-perfluorodecyltrichlorosilane) was prepared on the surface of a purchased single PTFE hollow fiber membrane (outer / inner diameter 1.4 / 0.8 mm, pore size 0.1 μm, porosity 80%). The polymerization mechanism of the PFDTS fluorosilane modifier on the surface of the hydroxylated modified PTFE hollow fiber membrane is as follows. Figure 4As shown, firstly, PFDTS molecules (RSiCl3) react with water molecules to remove HCl, forming the intermediate product RSi(OH)3. Then, numerous RSi(OH)3 molecules undergo dehydration condensation to form HO-[RSiO(OH)] n In the -RSi(OH)2 polymer state, due to the presence of abundant hydroxyl (OH) groups, the O atoms of the hydroxyl groups exhibit electrostatic attraction with the hydroxyl-rich base film material after hydroxylation treatment, leading to the formation of a broad hydrogen bond network. This hydrogen bond network is unstable and easily loses water molecules upon heating, resulting in HO-[RSiO(OH)] n -RSi(OH)2 polymer forms a stable -O- bond with the substrate, ultimately enabling PFDTS to grow on the substrate surface and form a hydrophobic layer.

[0030] Figure 5 The results show that the unmodified base membrane exhibits a porous outer surface with pore sizes generally below 1 μm, which is crucial for allowing water vapor to pass through without wetting. The inner surface displays regularly arranged elongated channels, resulting from the sintering and stretching processes during production. These channels are 5 × 50 μm in size, and the larger pore size ensures high flux. After fluorosilane surface modification, the inner surface showed no significant changes, while the outer surface clearly exhibited an uneven morphology due to the polymerization of the fluorosilane modifier. This is because after the PFDTS solution is injected into the hollow fiber membrane, the solution leaks from the large pores of the inner substrate to the outer layer, where it is trapped by the smaller pores. Due to the smaller pores in the outer layer, a more pronounced modification effect is achieved.

[0031] Figure 6 The results show that, on the outer surface of the modified hollow fiber membrane, in addition to its own C and F element distribution, a distinct and uniform distribution of Si and O elements was also detected, and their atomic percentage ratio is close to 2:1, which satisfies the Si / O atomic ratio of the PFDTS coating.

[0032] Figure 7 The infrared spectra of the outer surface of the PTFE hollow fiber membrane before and after modification are shown in the modified membrane at 1147 cm⁻¹. -1 and 1176cm -1 CF bond peaks were detected, consistent with the original base film. Furthermore, the modified film showed a peak at 1074 cm⁻¹. -1 and 1024 cm -1 Si-O bond peaks were detected in the range of 681-980 cm⁻¹. -1Peak clusters of Si-C bonds were detected. In the modified Si 2p XPS spectrum, obvious Si-C bond (102.7 eV) and Si-O bond (103.8 eV) peaks can be observed. The O 1s spectrum also shows more Si-O bond (532.9 eV) peaks than the original film before modification. All of these prove the successful growth and polymerization of the PFDTS coating.

[0033] Figure 8 SEM images and elemental analysis showed that after 7 days of alkaline treatment with 30 wt.% NaOH solution at 80 °C, the original membrane had a higher oxygen content than the modified membrane. Hydrophobicity tests on the outer surfaces of the original and modified membranes showed that the hydrophilic angle of the modified membrane increased from 112.5° in the original membrane to 154.2°, indicating a significant improvement in hydrophobicity. Dynamic hydrophilic angle testing also demonstrated the enhanced hydrophobicity of the modified membrane. The hydrophilic angle of the original membrane decreased to 107.6°, while the contact angle of the modified membrane remained at 127.9°. These results indicate a significant increase in the alkaline stability of the modified membrane, resulting in a significantly longer service life and enabling membrane distillation water supply under long-term alkaline conditions.

[0034] Example 2 According to the preparation method of perfluorosilane hydrophobic modification of PTFE hollow fiber membrane modules in the invention, the purchased PTFE hollow fiber membrane modules (membrane shell 4 with a length of 40cm, shell inner diameter of 3.3cm, membrane fiber 3 with an outer / inner diameter of 1.0 / 0.5mm, shell total volume of 30ml, total membrane area of ​​0.3㎡, membrane fiber pore size of 0.1μm, porosity of 80%, and number of membrane fibers of 216) and such Figure 3 The single-strand module with the membrane fiber arrangement shown has undergone hydrophobic modification. This Example 2 is mainly used to test the effect of hydrophobic modification on the water production performance of the PTFE hollow fiber membrane module.

[0035] Figure 9The apparatus flow chart describes the testing process for the water production performance (flux testing, influence of operating conditions, etc.) of the original and modified membrane modules. In this process, 30 wt.% alkali solution and 3.5 wt.% seawater are heated to 75°C and 80°C respectively in beakers of the alkali solution thermostat 11 and the seawater thermostat 9, and maintained at these temperatures. The two solutions are then pumped into the membrane distillation module 1 (the alkali solution and seawater are pumped into the shell side and tube side of the original and modified membrane distillation modules, respectively) by peristaltic pumps. After the flow rate is regulated by flow meter 8 and the temperature is measured by thermometer 6, the solutions are pumped into the membrane distillation module 1. Inside the membrane distillation module, the hot seawater evaporates a large amount of water vapor, which diffuses through the hollow fiber membrane pores to the shell side and liquefies, flowing into the alkali solution stream. Subsequently, the streams of alkali solution and seawater flow out of the module, and after the temperature is measured by thermometer 6, they flow back into the beakers of their respective thermostats. The entire process is repeated for several hours. To test the effect of seawater temperature on steam flux, under fixed conditions of alkali solution temperature and flow rate, and seawater flow rate, the seawater temperature was set to different values, and the weight change of the alkali solution constant temperature bath system was measured using a balance 10 to obtain the steam flux and water production. Similarly, to test the effect of seawater flow rate on steam flux, under fixed conditions of alkali solution temperature and flow rate, and seawater temperature, the seawater flow rate was set to different values, and the steam flux and water production were measured. In addition, the chloride ion concentration in the alkali solution stream at the membrane module outlet was measured using a chloride ion selective electrode 5 to reflect the ion separation performance of the hollow fiber membrane within the module and the stable operation of the monitoring device.

[0036] Figure 10 The figures show the water production performance (flux test, influence of operating conditions, etc.) of the original and modified membrane modules. Figure a shows the flux-seawater temperature curve, and Figure b shows the flux-seawater flow rate curve. During the test, the alkaline solution temperature and flow rate were maintained at 80℃ and 45 mL / min, respectively. In the experiment where seawater temperature affected flux, the seawater flow rate was 45 mL / min, and the temperature was set at 55℃, 65℃, and 75℃. In the experiment where seawater flow rate affected flux, the seawater temperature was 75℃, and the flow rate was set at 15 mL / min, 25 mL / min, and 45 mL / min, respectively. The test results show that after the membrane module was modified, i.e., after a hydrophobic layer was grown inside the hollow fiber membrane, the water vapor flux of the module was maintained and even increased slightly. In addition, with the increase of seawater temperature and flow rate, the water vapor pressure generated increased, thus strengthening the mass transfer driving force and gradually increasing the flux.

[0037] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A method for modifying alkali-resistant superhydrophobic PTFE hollow fiber membranes, characterized by: The method comprises the following steps: Step 1, oscillate or ultrasonic the PTFE hollow fiber membrane in organic solvent to fully infiltrate it; Step 2, heat treat the PTFE hollow fiber membrane obtained in step 1 in hydroxylated solution to obtain PTFE hollow fiber membrane with hydroxyl distributed on the surface; Step 3, rinse and soak the PTFE hollow fiber membrane obtained in step 2 with deionized water, and dry it at 30-80℃ for 1-8 hours; Step 4, prepare fluorosilane modifier solution with organic solvent, fill the PTFE hollow fiber membrane obtained in step 3 with the fluorosilane modifier solution, and tighten the two ends of the PTFE hollow fiber membrane, treat it at 20-80℃ for 30-150 seconds, then release the fluorosilane modifier solution in the PTFE hollow fiber membrane, heat the PTFE hollow fiber membrane in oven at 20-80℃ for 2-8 hours, then rinse it with deionized water, and dry it at 30-60℃ for 2-24 hours, form perfluorosilane hydrophobic layer on the PTFE hollow fiber membrane, and thus form alkali-resistant super-hydrophobic PTFE hollow fiber membrane.

2. The modification method of alkali-resistant super-hydrophobic PTFE hollow fiber membrane according to claim 1, characterized in that: The organic reagent comprises one or more of methanol solution, ethanol solution, isopropanol solution, and butanol solution; the oscillation or ultrasonic in step 1 is at 20-90℃ for 2-24 hours.

3. The modification method of alkali-resistant super-hydrophobic PTFE hollow fiber membrane according to claim 1, characterized in that: The hydroxylated solution is aqueous solution containing strong base and cationic surfactant, the strong base is sodium hydroxide or potassium hydroxide or calcium hydroxide, and the surfactant is one or more of dodecyl dimethyl benzyl ammonium chloride, dodecyl trimethyl ammonium chloride (bromide), hexadecyl trimethyl ammonium chloride (bromide), octadecyl trimethyl ammonium chloride (bromide), and didodecyl dimethyl ammonium chloride; The concentration ratio of the hydroxylated solution is 10-50wt% strong base and 2-20wt% cationic surfactant; the heat treatment is at 50-90℃ for 4-24 hours.

4. The modification method of alkali-resistant super-hydrophobic PTFE hollow fiber membrane according to claim 1, characterized in that: The fluorosilane modifier in step 4 comprises one or more of heptadecafluorodecyl trimethoxysilane, perfluorodecyl trichlorosilane, perfluorododecyl trichlorosilane, perfluorooctyl triethoxysilane, octadecyl trichlorosilane, trichlorododecylsilane, and octyl trichlorosilane; The organic solvent used in the fluorosilane modifier solution comprises one or more of methanol, ethanol, isopropanol, and butanol, and the solution concentration is 10-50wt%.

5. A method of modifying an alkali-resistant superhydrophobic PTFE hollow fiber membrane module, characterized by: The method comprises the following steps: Step 1, first fill the PTFE hollow fiber membrane assembly with organic solvent from the tube side inlet, and oscillate or stand still to wet it; Step 2, prepare hydroxylated solution, fill the PTFE hollow fiber membrane assembly obtained in step 1 with the hydroxylated solution, and heat treat the PTFE hollow fiber membrane assembly in oven to obtain PTFE hollow fiber membrane assembly with hydroxyl distributed on the surface; Step 3, rinse and soak the PTFE hollow fiber membrane assembly obtained in step 2 with deionized water by using peristaltic pump, and dry it by blowing air flow; Step 4, the fluorosilane modifier solution is prepared by using an organic solvent, and the fluorosilane modifier solution is heated, and then is uniformly flowed through the tubular path of the PTFE hollow fiber membrane module with the hydroxyl groups distributed on the surface in step 3 under the pushing of the peristaltic pump, and the PTFE hollow fiber membrane module with the hydroxyl groups distributed on the surface is heated in an oven to form a perfluorosilane super-hydrophobic layer, and then is washed by using deionized water and dried by blowing air flow to obtain the modified PTFE hollow fiber membrane module.

6. The modification method of an alkali-resistant superhydrophobic PTFE hollow fiber membrane module according to claim 5, characterized in that: The organic reagent includes one or more of a methanol solution, an ethanol solution, an isopropanol solution, and a butanol solution. The oscillation or standing in step 1 is at 20-90°C for 12-48 hours.

7. The modification method of an alkali-resistant super-hydrophobic PTFE hollow fiber membrane module according to claim 5, characterized in that: The hydroxylation solution is an aqueous solution containing a strong base and a cationic surfactant, the strong base is selected from sodium hydroxide, potassium hydroxide, or calcium hydroxide, and the surfactant is one or more of dodecyl dimethyl benzyl ammonium chloride, dodecyl trimethyl ammonium chloride (bromide), hexadecyl trimethyl ammonium chloride (bromide), octadecyl trimethyl ammonium chloride (bromide), and didodecyl dimethyl ammonium chloride. The concentration of the hydroxylation solution is 10-50 wt% of the strong base and 2-20 wt% of the cationic surfactant, and the heat treatment is at 50-90°C for 4-24 hours.

8. The modification method of an alkali-resistant super-hydrophobic PTFE hollow fiber membrane module according to claim 5, characterized in that: The flow rate of the peristaltic pump in step 3 is set to 10-100 mL / min, and the washing and soaking of the deionized water are at 20-60°C for 4-24 hours, and the temperature and flow rate of the dry air flow blown in are 20-80°C and 10-100 mL / min, respectively.

9. The modification method of an alkali-resistant super-hydrophobic PTFE hollow fiber membrane module according to claim 5, characterized in that: The fluorosilane modifier in step 4 includes one or more of heptadecafluorodecyl trimethoxysilane, perfluorodecyl trichlorosilane, perfluorododecyl trichlorosilane, perfluorooctyl triethoxysilane, octadecyl trichlorosilane, trichlorododecylsilane, and octyl trichlorosilane. The organic solvent used for the fluorosilane modifier solution includes one or more of methanol, ethanol, isopropanol, and butanol, and the solution concentration is 10-50 wt%, the solution heating temperature is 30-80°C, the flow rate of the peristaltic pump is set to 10-100 mL / min, the oven heating is at 20-80°C for 2-8 hours, the washing and soaking of the deionized water are at 20-60°C for 4-24 hours, and the temperature and flow rate of the dry air flow blown in are 20-80°C and 10-100 mL / min, respectively.

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