CN111773928A - Aerogel composite membrane and preparation method and application thereof - Google Patents
Aerogel composite membrane and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to an aerogel composite membrane and a preparation method and application thereof, wherein the aerogel composite membrane comprises a non-woven fabric support layer and an aerogel filling layer, the aerogel composite membrane has a multi-stage pore structure and comprises submicron/micron-sized pores with the pore diameter of 0.5-20 mu m and nanoscale pores with the pore diameter of 2-100nm, the thickness of the aerogel composite membrane is 0.1-1mm, the aerogel composite membrane obtained after normal pressure drying has excellent mechanical properties, good hydrophobicity and good heat insulation performance, and can be applied to the processes of treating seawater, high-salt wastewater and the like by using a membrane distillation technology, the water flux can reach 12.2LMH, and the salt cut-off rate is as high as 99.9%. Meanwhile, the solvent used in the preparation method is only water and alcohol, the aging and drying steps are carried out in an oven, and the subsequent treatment steps are not replaced by the solvent, so that the use of a large amount of organic solvent is avoided, the difficulty in waste liquid treatment is reduced, and the preparation method is more environment-friendly.
Description
Technical Field
The invention relates to the technical field of membrane distillation, relates to an aerogel composite membrane and a preparation method and application thereof, and particularly relates to an ultra-hydrophobic low-heat-conductivity aerogel composite membrane and a preparation method and application thereof.
Background
The high-salt industrial wastewater contains a large amount of soluble inorganic salt ions (such as Na)+，Cl-，K+，SO4 2-，NO3 -Etc.), salinity is usually greater than 1%, and is a type of industrial wastewater that is difficult to treat. Chemical industry, food industry, printing and dyeing industry, leather industry, pharmacy, petroleum industry, electric power industry, seawater desalination industry and the like can generate a large amount of high-salt industrial wastewater. The high-salinity wastewater discharged directly without treatment can cause huge environmental damage to soil, surface water and underground water. With the stricter environmental regulations, the zero emission of high-salinity wastewater is required in various industries, but the high investment and operation cost of the zero emission process greatly increases the popularization difficulty. The zero-emission process is mainly divided into three sections of pretreatment, concentration reduction and evaporation solidification, and the development of an efficient concentration technology for reducing the water load in the evaporation solidification process can remarkably reduce the operation cost of zero emission, so that the zero-emission process becomes a research focus in the industry.
Membrane distillation is a thermal membrane treatment technology with high concentration factor, which adopts a hydrophobic microporous membrane and takes the steam partial pressure difference at two sides of the membrane as a mass transfer driving force. The hydrophobicity of the membrane prevents aqueous solutions on both sides from permeating through the membrane pores to the other side, while the volatile component (water) in the feed solution on the hot side can evaporate at the membrane interface and diffuse through the dry hydrophobic micropores and be collected on the cold side. Since the vapor pressure of water is less affected by the ionic strength of water, membrane distillation concentrates the salt solution close to saturation. In addition, the operation temperature (about 60 ℃) of the membrane distillation is far lower than that of the traditional distillation process, so that low-grade heat energy such as industrial waste heat, solar energy, geothermal energy and the like can be effectively utilized, and the energy consumption problem in the evaporation process is greatly reduced. Therefore, the membrane distillation has wide application prospect in the fields of seawater desalination, wastewater treatment, beverage concentration, medical pharmacy and the like.
Despite the extensive research on membrane distillation over the past few decades, membrane distillation has not been commercialized to date, and the bottleneck problem is the lack of a commercial membrane distillation membrane with excellent performance. The membrane for membrane distillation should have strong hydrophobicity to prevent hot side feed liquid from directly entering the permeation side (i.e. membrane infiltration phenomenon) during long-term use, and also needs good heat insulation performance to reduce heat loss during membrane distillation. The current laboratory preparation methods of the membrane distillation membrane mainly comprise a phase inversion method and an electrostatic spinning method. The phase inversion method is an efficient method for preparing the porous membrane at present, but the membrane prepared by the phase inversion method has poor hydrophobicity and generally needs complex post-treatment. The membrane prepared by the electrostatic spinning method has good hydrophobicity, but the electrostatic spinning technology is complex, the membrane preparation efficiency is low, and the membrane distillation membrane is not beneficial to large-scale preparation. In addition, a large amount of waste organic solvent is generated in the processes of film preparation by a phase inversion method and electrostatic spinning, and potential harm is caused to the environment. In addition, although the membrane distillation can effectively utilize industrial waste heat, the thermal efficiency of the membrane distillation is still far lower than that of other thermal method concentration processes, so that the improvement of the thermal efficiency of the membrane distillation has important significance for reducing the energy consumption of the membrane distillation and promoting the long-term development of the membrane distillation. Reducing the heat transfer loss of the membrane is an efficient measure for improving the thermal efficiency of membrane distillation, but due to the limitations of membrane materials and preparation methods, few studies are currently made to improve the thermal efficiency of membrane distillation by reducing the thermal conductivity of the membrane while ensuring a suitable membrane thickness. Therefore, the invention discloses a green, economic and efficient method for preparing the ultra-hydrophobic low-heat-conduction membrane distillation membrane with proper thickness, which has important significance.
Patent TWI577565B discloses a hydrophobic porous silica aerogel composite membrane suitable for vacuum type membrane distillation apparatus and a vacuum membrane distillation method, the hydrophobic porous silica aerogel composite membrane is obtained by compounding aerogel and porous alumina membrane, the composite membrane comprises a porous alumina membrane support layer and a porous silica aerogel surface layer. The aerogel surface layer is synthesized by sol-gel with methyltrimethoxysilane as a precursor. Soaking the porous alumina membrane in the aerogel sol solution and maintaining for a period of time to form gel (about 24 hours), then taking out the membrane with the gel on the surface, placing the membrane in ethanol for aging (about 48 hours), performing solvent replacement by using normal hexane (about 24 hours) after aging, and finally drying to obtain the hydrophobic porous silicon dioxide aerogel composite membrane. The operation can generate a large amount of organic waste liquid, the membrane preparation period is long, and the post-treatment step is complicated. The average pore diameter of the surface layer of the prepared hydrophobic porous silica aerogel is small (2-50nm), and the porosity of the alumina supporting membrane is low, so that the water flux of the membrane in direct contact membrane distillation is low.
Disclosure of Invention
In order to solve the problems of large potential environmental pollution, high cost, high coefficient of heat conductivity of the prepared membrane and the like in the preparation process of the conventional membrane distillation membrane, the invention prepares a composite wet membrane by taking non-woven fabrics as a filling framework through a sol-gel process, and the wet membrane is directly dried under normal pressure to obtain the super-hydrophobic low-heat-conductivity membrane distillation membrane with proper aperture. The problem of inherent brittleness of the aerogel is well solved by taking the non-woven fabric as the filling framework, and the mechanical strength of the membrane distillation membrane is ensured. In addition, the solvent used in the invention is only alcohol and water, and solvent replacement and other complicated pretreatment steps are not needed before drying, so that the preparation process is very green and simple.
The invention provides an aerogel composite membrane, which comprises a non-woven fabric supporting layer and an aerogel filling layer, wherein the aerogel composite membrane has a multi-stage pore structure and comprises submicron/micron-scale pores with the pore diameter of 0.5-20 mu m and nanometer-scale pores with the pore diameter of 2-100 nm.
In some embodiments, the aerogel composite membrane has a thickness of 0.1 to 1mm, and preferably the aerogel composite membrane has a thickness of 0.3 to 0.6 mm.
In some embodiments, the hydrophobic angle of the aerogel composite membrane is 130 ° to 160 °, and preferably the hydrophobic angle of the aerogel composite membrane is 150 ° to 160 °.
In some embodiments, the aerogel composite membrane has a thermal conductivity of 0.02 to 0.05 WK-1·m-1。
In the invention, the non-woven fabric in the aerogel composite film plays a supporting role, the aerogel is filled in the pores of the aerogel composite film, and the filled aerogel has a multi-level pore structure and comprises submicron/micron-level pores with the pore diameter of 0.5-20 mu m and nanometer-level pores with the pore diameter of 2-100nm, wherein the submicron/micron-level pores not only provide a water vapor channel, but also ensure the heat-insulating property of the composite film together with the nanometer-level pores. In addition, the thickness of the aerogel composite membrane significantly affects the transmission resistance of water vapor during membrane distillation, so reducing the thickness of the membrane helps to increase water flux, while too thin a membrane reduces the mechanical properties, thermal insulation properties, and service life of the membrane. Therefore, in order to balance the water flux of the membrane, the mechanical properties of the membrane and the thermal insulation properties of the membrane, the thickness of the aerogel composite membrane disclosed by the invention is controlled to be between 0.1 and 1mm, and preferably between 0.3 and 0.6 mm.
In some specific embodiments, the sub-micron/micron pores have a pore size of 0.5 to 20 μm; and/or the aperture of the nanometer-scale hole is 2-100 nm; and/or the hydrophobic angle of the aerogel composite membrane is 130-160 degrees; and/or the thermal conductivity coefficient of the aerogel composite membrane is 0.02-0.05 W.K-1·m-1。
In some embodiments, the nonwoven fabric is a hydrophobic nonwoven fabric.
In some embodiments, the nonwoven fabric preferably comprises one or more of a PP nonwoven fabric, a PET nonwoven fabric, a PTFE nonwoven fabric, a PP/PET nonwoven fabric, a PTFE/PP nonwoven fabric, and a PTFE/PET nonwoven fabric.
In some embodiments, the aerogel is a silica aerogel, preferably a silica aerogel.
The invention also provides a preparation method of the aerogel composite membrane, which comprises the following steps:
1) preparing a sol solution comprising alkoxysilane, alcohol and water;
2) dipping the non-woven fabric into the sol solution, taking out the non-woven fabric, placing the non-woven fabric into a mold, standing the non-woven fabric, performing aging treatment, and drying the non-woven fabric to obtain the super-hydrophobic low-heat-conductivity aerogel composite membrane;
wherein, the relative pressure of the composite film in the die in the standing and aging treatment is 1-400Pa, preferably 50-200Pa, and more preferably 80-120 Pa.
In some embodiments, the mass ratio of alkoxysilane, alcohol, and water in step 1) is alkoxysilane: alcohol: water (0.5-1): (0.5-4): 0.5-4).
In some preferred embodiments, the mass ratio of alkoxysilane, alcohol and water in step 1) is alkoxysilane: alcohol: water (0.7-1): (1.5-3): 1-2).
In a preferred embodiment, the mass ratio of alkoxysilane, alcohol and water in step 1) is alkoxysilane: alcohol: water-1: 2.5: 1.5.
In some embodiments, the alkoxysilane comprises one or more of methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane.
In some preferred embodiments, the alkoxysilane is methyltriethoxysilane.
In some embodiments, the alcohol comprises one or more of methanol, ethanol, isopropanol, ethylene glycol, propylene glycol.
In some preferred embodiments, the alcohol is ethanol.
In some embodiments, the step 1) comprises:
1A) mixing alkoxy silane, alcohol and water to obtain sol solution;
1B) and adjusting the pH value of the sol solution to 9-10 to obtain the sol.
In some specific embodiments, the alkoxysilane is mixed with the alcohol and water in step 1A) for 10 to 40 hours to obtain a sol solution.
In some specific embodiments, in the step 1B), ammonia water is added to the sol solution, the pH value of the sol is adjusted to 9-10, and then the sol is stirred at a temperature of 0-90 ℃ for 0.5-5 hours, so as to obtain the sol.
In some embodiments, the step 2) comprises:
2A) dipping the non-woven fabric into the sol solution to fully fill the pores and the surface of the non-woven fabric, taking out the dipped non-woven fabric, placing the dipped non-woven fabric in a mould, standing for gelling, and aging to obtain a wet film;
2B) and drying the wet film to obtain the super-hydrophobic low-heat-conductivity aerogel composite film.
In some specific embodiments, the mold in step 2A) is a closed container, which can ensure that water and alcohol do not volatilize during the gelation process.
In some specific embodiments, the mold in step 2A) is a closed flat mold, and the material of the mold is one or more of organic glass, stainless steel, ceramic, PP (polyethylene), PE (polypropylene), PVC (polyvinyl chloride), and ABS (acrylonitrile/butadiene/styrene copolymer).
In some preferred embodiments, the mold is made of glass.
In some embodiments, the aging in step 2A) is performed at a temperature of 25 to 90 ℃ for 1 to 24 hours.
In some specific embodiments, the drying in step 2B) is atmospheric drying, the drying temperature is 50 to 90 ℃, and the drying time is 1 to 24 hours.
The invention also provides application of the aerogel composite membrane in the first aspect or the aerogel composite membrane prepared by the preparation method in the second aspect in membrane distillation.
The invention provides an ultra-hydrophobic low-heat-conduction aerogel composite film, which comprises a non-woven fabric supporting layer and an aerogel filling layer, wherein the thickness of the aerogel composite film is 0.1-1mm, the non-woven fabric in the aerogel composite film plays a supporting role, aerogel is filled in pores of the aerogel composite film, the filled aerogel has a multi-stage pore structure and comprises submicron/micron-scale pores with the pore diameter of 0.5-20 mu m and nanoscale pores with the pore diameter of 2-100nm, wherein the submicron/micron-scale pores not only provide a water vapor channel, but also ensure the heat-insulating property of the composite film together with the nanoscale pores, so that the water flux of the ultra-hydrophobic low-heat-conduction aerogel composite film obtained by the invention can reach 12.2LMH (L.m)-2·h-1) The salt cut-off rate is higher than 99.9 percent, the hydrophobic angle is as high as 152 degrees, and the heat conductivity coefficient is as low as 0.04 W.m-1·K-1. And provideThe aerogel composite membrane obtained by the preparation method of the membrane has excellent mechanical properties, good hydrophobicity, good heat resistance and heat insulation performance, and can be applied to the processes of treating seawater, high-salinity wastewater and the like by using a membrane distillation technology. According to the preparation method disclosed by the invention, only water and alcohol are used as solvents, the aging and drying steps are carried out in the oven, and the subsequent treatment steps are not replaced by the solvents, so that the use of a large amount of organic solvents is avoided, the difficulty in waste liquid treatment is reduced, the preparation method is more green and environment-friendly, and the obtained super-hydrophobic low-thermal-conductivity aerogel composite membrane can be further subjected to surface function modification to meet different requirements.
Drawings
Fig. 1 is a scanning electron microscope image of the super-hydrophobic low thermal conductivity aerogel composite film prepared in example 1.
Fig. 2 is a water contact angle diagram of the super-hydrophobic low thermal conductive aerogel composite membrane prepared in example 1.
FIG. 3 is a stress-strain curve diagram of the super-hydrophobic low thermal conductivity aerogel composite film prepared in example 1
Fig. 4 is a graph of the thermal conductivity of the super-hydrophobic low thermal conductivity aerogel composite membrane prepared in example 1 and a commercial hydrophobic membrane.
FIG. 5 is a distribution diagram of the pore diameter of the super-hydrophobic low thermal conductivity aerogel composite membrane prepared in example 1.
Fig. 6 is a graph of the test results of the water flux and the salt cut-off rate of the super-hydrophobic low thermal conductivity aerogel composite membrane prepared in example 1 measured by a direct contact membrane distillation method.
FIG. 7 is a graph showing the results of measuring the water flux of the membrane CM-L prepared in comparative example 2 by the direct contact membrane distillation method.
Detailed Description
In order that the present invention may be more readily understood, the following detailed description of the invention is given by way of example only, and is not intended to limit the scope of the invention.
Unless otherwise indicated, the procedures and treatments referred to in this invention are conventional in the art, and the apparatus used in this invention is conventional in the art, and the chemicals used in this invention are commercially available.
The detection method related in the specific embodiment of the invention is as follows:
the scanning electron microscope adopts a Hitachi S-4800 Japanese scanning electron microscope;
the water contact angle, the sliding angle, was determined using a water contact angle meter (precision Test, china);
the stress-strain curve is measured by using a universal material tester (Kaibolili KD-II 10/100N, China)
The thermal conductivity is measured by a thermal conductivity meter (Hot-Disk, TPS 2500S, Switzerland);
the pore size distribution of the composite membrane is measured by a mercury intrusion instrument (AutoPore Iv 9510, USA);
the commercial hydrophobic membrane was a PVDF membrane (HVSP, Millipore) with a thickness of 0.098 mm.
Example 1
Mixing methyl triethoxysilane with ethanol and water at a mass ratio of 1:2.5:1.5, and stirring at room temperature for 24 hours to obtain sol solution with uniform properties; then, adding ammonia water to adjust the pH value of the sol solution to 9-10, and stirring for 1 hour; immersing a PP non-woven fabric (with the thickness of about 0.45mm) in the sol solution after pH adjustment, taking out and placing in a glass flat plate mould, controlling the relative pressure to be 100Pa, standing for 10 hours, and then transferring to a 50 ℃ oven for aging for 5 hours to prepare a wet film; and finally, taking the wet film out of the die, and drying the wet film in an oven at 80 ℃ for 1 hour to obtain the super-hydrophobic low-heat-conductivity aerogel composite film.
The average thickness of the aerogel composite membrane is 0.48mm, the microscopic surface appearance of the aerogel composite membrane is shown in figure 1, and silica particles formed by sol-gel are stacked in pores of the non-woven fabric to form a three-dimensional network structure with rich holes. The aerogel composite membrane has a water contact angle as high as 152 degrees (figure 2), a sliding angle as low as 6.5 degrees, a super-hydrophobic level and excellent mechanical properties (figure 3). Transmembrane heat loss during membrane distillation is mainly caused by heat conduction through the membrane, the heat flux Q conducted through the membranemCan be calculated by the following formula:
where λ is the thermal conductivity of the film, and is the thickness of the film, Tf,mAnd Tp,mThe average temperatures of the feed side membrane surface and the permeate side membrane surface, respectively. When the membrane surface temperature conditions are the same, λ/is the main factor determining the heat flux conducted by the membrane. As can be seen from the thermal conductivity test of the aerogel composite membrane (shown in figure 4), compared with a commercial hydrophobic membrane, the thermal conductivity of the aerogel composite membrane is 62.1% of that of the commercial membrane, and the thickness of the aerogel composite membrane is about 5 times of that of the commercial membrane, so that the conduction heat loss of the aerogel composite membrane is only 12.5% of that of the commercial membrane under the same temperature difference, and the thermal efficiency of the membrane distillation process is greatly improved. In addition, the aperture of the holes of the composite membrane is 6-15 μm and 10-1000nm (figure 5).
Example 2
Mixing methyltrimethoxysilane, ethanol and water according to the mass ratio of 1:2.5:1.5, and stirring at room temperature for 24 hours to obtain sol solution with uniform properties; then, adding ammonia water to adjust the pH value of the sol solution to 9-10, and stirring for 1 hour; soaking the PP non-woven fabric in the sol solution after the pH is adjusted, taking out the PP non-woven fabric, placing the PP non-woven fabric in a glass flat plate mould, controlling the relative pressure to be 100Pa, standing for 10 hours, and then transferring the PP non-woven fabric to a 50 ℃ oven for aging for 5 hours to prepare a wet film; and finally, taking the wet film out of the die, and drying the wet film in an oven at 80 ℃ for 1 hour to obtain the super-hydrophobic low-heat-conductivity aerogel composite film. The hydrophobic angle of the aerogel composite membrane is 154 degrees, the sliding angle is 8 degrees, and the heat conductivity coefficient is 0.035 W.K-1·m-1。
Example 3
Mixing methyl triethoxysilane with ethanol and water at a mass ratio of 1:2.5:1.5, and stirring at room temperature for 24 hours to obtain sol solution with uniform properties; then, adding ammonia water to adjust the pH value of the sol solution to 9-10, and stirring for 1 hour; soaking the PTFE/PP non-woven fabric in the sol solution after the pH is adjusted, taking out the non-woven fabric, placing the non-woven fabric in a glass flat plate mold, controlling the relative pressure to be 100Pa, standing for 10 hours, and then transferring the non-woven fabric to a 50 ℃ oven for aging for 5 hours to prepare a wet film; finally, taking out the wet film from the mold, and drying the wet film in an oven at the temperature of 80 ℃ for 1 hour to obtain the hydrophobic low-heat-conductivity aerogel complexAnd (5) combining the films. The hydrophobic angle of the aerogel composite membrane is 140 degrees, the sliding angle is 28 degrees, and the heat conductivity coefficient is 0.053 W.K-1·m-1。
Example 4
Mixing methyl triethoxysilane, dimethyl diethoxy silane, ethanol and water according to the mass ratio of 0.8:0.2:2.5:1.5, and stirring at room temperature for 24 hours to obtain sol solution with uniform properties; then, adding ammonia water to adjust the pH value of the sol solution to 9-10, and stirring for 1 hour; soaking the PP non-woven fabric in the sol solution after the pH is adjusted, taking out the PP non-woven fabric, placing the PP non-woven fabric in a glass flat plate mould, controlling the relative pressure to be 100Pa, standing for 10 hours, and then transferring the PP non-woven fabric to a 50 ℃ oven for aging for 5 hours to prepare a wet film; and finally, taking the wet film out of the die, and drying the wet film in an oven at the temperature of 80 ℃ for 1 hour to obtain the hydrophobic low-heat-conductivity aerogel composite film. The hydrophobic angle of the aerogel composite membrane is 145 degrees, the sliding angle is 25 degrees, and the heat conductivity coefficient is 0.051 W.K-1·m-1。
Example 5
Mixing methyltrimethoxysilane, methanol and water according to the mass ratio of 1:2.5:1.5, and stirring at room temperature for 24 hours to obtain sol solution with uniform properties; then, adding ammonia water to adjust the pH value of the sol solution to 9-10, and stirring for 1 hour; soaking the PP non-woven fabric in the sol solution after the pH is adjusted, taking out the PP non-woven fabric, placing the PP non-woven fabric in a glass flat plate mould, controlling the relative pressure to be 100Pa, standing for 10 hours, and then transferring the PP non-woven fabric to a 50 ℃ oven for aging for 5 hours to prepare a wet film; and finally, taking the wet film out of the die, and drying the wet film in an oven at 80 ℃ for 1 hour to obtain the super-hydrophobic low-heat-conductivity aerogel composite film. The hydrophobic angle of the aerogel composite membrane is 154 degrees, the sliding angle is 6 degrees, and the heat conductivity coefficient is 0.035 W.K-1·m-1。
Example 6
Mixing methyl triethoxysilane with ethanol and water at a mass ratio of 1:2.5:1.5, and stirring at room temperature for 24 hours to obtain sol solution with uniform properties; then, adding ammonia water to adjust the pH value of the sol solution to 9-10, and stirring for 1 hour; immersing PP non-woven fabric in the sol solution after pH adjustment, taking out the PP non-woven fabric, placing the PP non-woven fabric in a glass flat plate mould, controlling the relative pressure to be 100Pa, standing for 5 hours, and then transferring the PP non-woven fabric to a 50 ℃ ovenAging for 5 hours to obtain a wet film; and finally, taking the wet film out of the die, and drying the wet film in an oven at the temperature of 80 ℃ for 1 hour to obtain the hydrophobic low-heat-conductivity aerogel composite film. The hydrophobic angle of the aerogel composite membrane is 140 degrees, the sliding angle is 16 degrees, and the heat conductivity coefficient is 0.051 W.K-1·m-1。
Example 7
Mixing methyltriethoxysilane, ethanol and water according to the mass ratio of 0.7:2.5:1.5, and stirring at room temperature for 24 hours to obtain sol solution with uniform properties; then, adding ammonia water to adjust the pH value of the sol solution to 9-10, and stirring for 1 hour; soaking the PP non-woven fabric in the sol solution after the pH is adjusted, taking out the PP non-woven fabric, placing the PP non-woven fabric in a ceramic flat plate mould, controlling the relative pressure to be 100Pa, standing for 10 hours, and then transferring the PP non-woven fabric to a 50 ℃ oven for aging for 5 hours to prepare a wet film; and finally, taking the wet film out of the die, and drying the wet film in an oven at 80 ℃ for 1 hour to obtain the super-hydrophobic low-heat-conductivity aerogel composite film. The hydrophobic angle of the aerogel composite membrane is 150 degrees, the sliding angle is 6 degrees, and the heat conductivity coefficient is 0.039 W.K-1·m-1。。
Application example 1
To test the membrane distillation performance of the low thermal conductivity super-hydrophobic aerogel composite membrane prepared in example 1, a 3.5 wt% sodium chloride solution was used as a feed solution, deionized water was used as a permeate solution, and the feed solution temperature was controlled at 60 ℃, the permeate solution temperature was controlled at 20 ℃, the flow rate in the pipeline was 0.4L/min, and the water flow cross-flow rate on the membrane surface was 6.3 cm/s. The water flux was calculated from the change in mass of water on the permeate side and the salt cut was calculated by measuring the change in conductivity on the permeate side, the specific data being shown in fig. 6.
As can be seen from fig. 6, the super-hydrophobic low thermal conductivity aerogel composite membrane prepared in example 1 has a higher water flux, which can reach 12.2LMH, and a salt cut-off rate thereof is as high as 99.9% under a direct contact membrane distillation test.
Comparative example 1
Mixing methyl triethoxysilane with ethanol and water at a mass ratio of 1:2.5:1.5, and stirring at room temperature for 24 hours to obtain sol solution with uniform properties; then, adding ammonia water to adjust the pH value of the sol solution to 9-10, and stirring for 1 hour; placing the PP non-woven fabric on a glass flat plate, uniformly pouring the sol solution on the non-woven fabric, removing the redundant sol solution on the surface of the membrane by using a glass rod, and standing for 10 hours.
Since the solvent is a mixture of water and alcohol, it will volatilize rapidly in open environment, cannot form a uniform gel layer, and the formed gel is easy to fall off and cannot be used as a membrane distillation membrane
Comparative example 2
A method for preparing a porous silica aerogel composite membrane is reported in the document [ Perform of ceramic membrane in vacuum membrane distillation and in vacuum membrane crystallization ], Chia-Chieh Ko et al, desalinization, 440(2018), pages 48-58, published 3/30/2018 ], and specifically as follows:
mixing methyltrimethoxysilane (MTMS), ethanol (EtOH) and hydrochloric acid (HCl) in deionized water, and stirring at room temperature for 90 minutes to obtain sol with uniform property, wherein the molar ratio of MTMS to EtOH to HCl to deionized water is 1:3 (6.9 × 10)-4):1. Then, ethanol and ammonia (NH) were added in a molar ratio of 1:0.223:2.123·H2O) and deionized water, stirred at room temperature for 30 minutes. And then, soaking the alumina tubular membrane in the sol solution for 1 day to obtain the aerogel composite membrane. And then, soaking the aerogel composite membrane in ethanol for aging for 2 days, and soaking the aged aerogel composite membrane in n-hexane for 1 day of solvent replacement. And finally, drying the aerogel composite membrane subjected to solvent replacement at room temperature and normal pressure to obtain the aerogel composite membrane (CM-L).
The CM-L membrane is subjected to direct contact membrane distillation performance test by using pure water as a feed liquid, the temperature of the feed liquid is controlled to be about 50 ℃, the cross flow of a pipeline is controlled to be 0.3L/min, and the water flux is calculated through the mass change of water on the permeation side, wherein the specific data are shown in figure 7.
Comparing the water flux data of example 1 and comparative example 2, it can be seen from fig. 7 that the water flux of the CM-L film using the aluminum oxide film as the support layer is maintained at about 0.6LMH after 60 minutes, while it can be seen from fig. 6 that the water flux of the aerogel composite film using the non-woven fabric as the support layer according to the present invention can be as high as 12.2LMH, and it can be seen that the super-hydrophobic low thermal conductive aerogel composite film prepared by using the method of the present invention has a higher water flux. Meanwhile, the invention avoids the step of solvent replacement in the preparation process, thereby being more energy-saving and environment-friendly.
It should be noted that the above-mentioned embodiments are only for explaining the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. The invention can be modified, as prescribed, within the scope of the claims and without departing from the scope and spirit of the invention. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein, but rather extends to all other methods and applications having the same functionality.
Claims (10)
1. An aerogel composite membrane comprises a non-woven fabric support layer and an aerogel filling layer; wherein the aerogel composite membrane has a multi-level pore structure and comprises submicron/micron pores with the pore diameter of 0.5-20 mu m and nanometer pores with the pore diameter of 2-100 nm; and/or the thickness of the aerogel composite membrane is 0.1-1mm, and preferably the thickness of the aerogel composite membrane is 0.3-0.6 mm.
2. The aerogel composite membrane of claim 1, wherein the nonwoven fabric is a hydrophobic nonwoven fabric; preferably, the non-woven fabric comprises one or more of PP non-woven fabric, PET non-woven fabric, PTFE non-woven fabric, PP/PET non-woven fabric, PTFE/PP non-woven fabric and PTFE/PET non-woven fabric; and/or, the aerogel is a silica aerogel, preferably a silica aerogel.
3. A method of preparing the aerogel composite membrane of claim 1 or 2, comprising:
1) preparing a sol solution comprising alkoxysilane, alcohol and water;
2) dipping a non-woven fabric into the sol solution, taking out the non-woven fabric, placing the non-woven fabric into a mold, standing the non-woven fabric, performing aging treatment, and then performing drying treatment to obtain the super-hydrophobic low-heat-conductivity aerogel composite membrane;
wherein, the relative pressure of the composite film in the die in the standing and aging treatment is 1-400Pa, preferably 50-200Pa, and more preferably 80-120 Pa.
4. The production method according to claim 3, wherein the mass ratio of the alkoxysilane, the alcohol, and the water in step 1) is an alkoxysilane: alcohol: water (0.5-4): (0.5-4): 0.5-4); preferably (0.7-2): (1.5-3): 1-2), more preferably 1:2.5: 1.5.
5. The method according to claim 3 or 4, wherein the alkoxysilane comprises one or more of methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, preferably methyltriethoxysilane; and/or the alcohol comprises one or more of methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, preferably ethanol.
6. The method for preparing according to any one of claims 3 to 5, wherein the step 1) comprises:
1A) mixing alkoxy silane, alcohol and water to obtain sol solution;
1B) and adjusting the pH value of the sol solution to 9-10 to obtain the sol.
7. The production method according to any one of claims 4 to 6, wherein the alkoxysilane is mixed with the alcohol and water in step 1A), and the mixture is stirred for 10 to 40 hours to obtain a sol solution; and/or adding ammonia water into the sol solution in the step 1B), adjusting the pH value of the sol to 9-10, and then stirring for 0.5-5 hours at the temperature of 0-90 ℃ to obtain the sol.
8. The method for preparing according to any one of claims 4 to 7, wherein the step 2) comprises:
2A) dipping the non-woven fabric into the sol solution to fully fill the pores and the surface of the non-woven fabric, taking out the dipped non-woven fabric, placing the dipped non-woven fabric in a mould, standing for gelling, and aging to obtain a wet film;
2B) and drying the wet film to obtain the super-hydrophobic low-heat-conductivity aerogel composite film.
9. The method according to any one of claims 4 to 8, wherein the mold in step 2A) is a flat mold, preferably a closed flat mold, made of one or more of organic glass, stainless steel, ceramic, polyethylene, polypropylene, polyvinyl chloride and acrylonitrile/butadiene/styrene copolymer, more preferably glass; and/or, the temperature of aging in the step 2A) is 25-90 ℃ and the time is 1-24 hours; and/or the drying in the step 2B) is normal pressure drying, the drying temperature is 50-100 ℃, and the drying time is 1-24 hours.
10. Use of the aerogel composite membrane according to claim 1 or 2 or prepared according to the preparation method of any one of claims 3 to 9 in membrane distillation.
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