WO2022000608A1

WO2022000608A1 - Aerogel composite membrane, preparation method therefor and use thereof

Info

Publication number: WO2022000608A1
Application number: PCT/CN2020/103237
Authority: WO
Inventors: 郑煜铭; 王停宇; 邵再东
Original assignee: 中国科学院城市环境研究所
Priority date: 2020-07-02
Filing date: 2020-07-21
Publication date: 2022-01-06
Also published as: CN111773928B; CN111773928A

Abstract

An aerogel composite membrane, a preparation method therefor and the use thereof. The aerogel composite membrane includes a non-woven fabric supporting layer and an aerogel filling layer. The aerogel composite membrane has a multi-sized pore structure, which includes submicron/micron-sized pores having a pore size of 0.5-20 μm and nano-sized pores having a pore size of 2-100 nm. The thickness of the aerogel composite membrane is 0.1-1 mm. The aerogel composite membrane obtained after drying at a normal pressure has an excellent mechanical property, good hydrophobicity, relatively good heat insulation performance, and can be applied in membrane distillation technology for treating seawater, high-salinity wastewater, etc., wherein a water flux can reach 12.2 LMH, and the salt rejection rate reaches up to 99.9%. In addition, the solvents used in the preparation method are merely water and an alcohol, aging and drying steps are carried out in an oven, and solvent replacement is not used in subsequent treatment steps, such that the use of a large amount of an organic solvent is avoided and the difficulty of waste liquid treatment is reduced. The method is more green and environmentally friendly.

Description

A kind of aerogel composite membrane and preparation method and application

This application claims to enjoy the priority of the Chinese patent application titled "Aerogel composite membrane and its preparation method and application" filed on July 2, 2020, and the application number is CN202010634595.1, the entire content of which is by reference Incorporated herein.

technical field

The invention relates to the technical field of membrane distillation, relates to an aerogel composite film, a preparation method and application thereof, and in particular relates to a super-hydrophobic and low thermal conductivity aerogel composite film, a preparation method and application thereof.

Background technique

High-salt industrial wastewater contains a large amount of dissolved inorganic salt ions (such as Na ⁺ , Cl ^- , K ⁺ , SO ₄ ^2- , NO ₃ ^-, etc.), and the salinity is usually greater than 1%. It is a kind of industrial wastewater that is difficult to treat. Chemical, food, printing and dyeing, tanning, pharmaceutical, petroleum, electric power, seawater desalination and other industries will produce a large amount of high-salt industrial wastewater. High-salt wastewater discharged directly without treatment will cause huge environmental damage to soil, surface water and groundwater. With the increasingly stringent environmental regulations, many industries have required "zero discharge" for high-salt wastewater. However, the high investment and operation cost of the zero-discharge process has greatly increased the difficulty of its promotion. The zero-emission process is mainly divided into three stages: pretreatment, concentration reduction, and evaporation and solidification. The development of efficient concentration technology to reduce the water load in the evaporation and solidification process can significantly reduce the operating cost of zero-emission, and has become a research focus in the industry.

Membrane distillation is a thermal membrane treatment technology with a high concentration factor, which uses a hydrophobic microporous membrane and uses the vapor partial pressure difference on both sides of the membrane as the driving force for mass transfer. The hydrophobicity of the membrane makes it impossible for the aqueous solution on both sides to pass through the membrane pores and enter the other side, while the volatile components (water) in the feed liquid on the hot side can evaporate and diffuse through the dry hydrophobic micropores at the membrane interface, and are released in the cold. side to collect. Since the vapor pressure of water is less affected by the ionic strength of the water, membrane distillation can concentrate the salt solution to near saturation. In addition, the operating temperature of membrane distillation (about 60°C) is much lower than that of traditional distillation processes, which can effectively utilize low-grade thermal energy such as industrial waste heat, solar energy, and geothermal energy, which greatly reduces the energy consumption in the evaporation process. Therefore, membrane distillation has broad application prospects in the fields of seawater desalination, wastewater treatment, beverage concentration, and medical pharmaceuticals.

Despite a large number of membrane distillation studies in the past few decades, membrane distillation has not yet been commercialized, and its bottleneck is the lack of commercial membrane distillation membranes with excellent performance. The membrane for membrane distillation should have strong hydrophobicity to prevent the hot side feed liquid from directly entering the permeate side during long-term use (that is, the membrane infiltration phenomenon), and at the same time, good thermal insulation performance is required to reduce the heat of the membrane distillation process. loss. At present, the laboratory preparation methods of membrane distillation membranes mainly include phase inversion method and electrospinning method. The phase inversion method is currently an efficient method for preparing porous membranes, but the membranes prepared by phase inversion have poor hydrophobicity and usually require complex post-processing. The membrane prepared by the electrospinning method has good hydrophobicity, but the electrospinning technology is complicated and the membrane production efficiency is low, which is not conducive to the large-scale preparation of membrane distillation membrane. In addition, both the phase inversion method and the electrospinning method will generate a large amount of waste organic solvent during the film production process, which will cause potential harm to the environment. In addition, although membrane distillation can effectively utilize industrial waste heat, its thermal efficiency is still much lower than that of other thermal concentration processes. Therefore, improving the thermal efficiency of membrane distillation is of great significance to reduce the energy consumption of membrane distillation and promote the long-term development of membrane distillation. Reducing the heat transfer loss of the membrane is an efficient measure to improve the thermal efficiency of membrane distillation. However, due to the limitations of membrane materials and preparation methods, there are few studies to improve the thermal efficiency of membrane distillation by reducing the thermal conductivity of the membrane while ensuring a suitable membrane thickness. . Therefore, it is of great significance to invent a green, economical and efficient method to prepare superhydrophobic and low thermal conductivity membrane distillation films with suitable thickness.

Patent TWI577565B discloses a hydrophobic porous silica aerogel composite membrane suitable for a vacuum membrane distillation device and a vacuum membrane distillation method. The hydrophobic porous silica gas is obtained by compounding the aerogel and the porous alumina membrane The gel 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 using methyltrimethoxysilane as a precursor. The porous alumina membrane was immersed in the aerogel sol solution and maintained for a period of time to form a gel (about 24 hours), and then the membrane with the gel on the surface was taken out and placed in ethanol for aging (about 48 hours). The solvent was replaced with n-hexane (about 24 hours), and finally dried to obtain a hydrophobic porous silica aerogel composite membrane. The above operations will generate a large amount of organic waste liquid, the film-making cycle is long, and the post-processing steps are cumbersome. The prepared hydrophobic porous silica aerogel surface layer has a small average pore size (2-50 nm), and the alumina support membrane has low porosity, resulting in a very low water flux in the direct-contact membrane distillation.

SUMMARY OF THE INVENTION

In order to solve the problems of high potential environmental pollution, high cost and high thermal conductivity of the prepared membrane during the preparation process of the existing membrane distillation membrane, the present invention uses non-woven fabric as the filling skeleton, and obtains a composite wet membrane through a sol-gel process. The wet membrane is often pressed A superhydrophobic and low thermal conductivity membrane distillation membrane with suitable pore size can be obtained by direct drying. The use of non-woven fabrics as the filling framework solves the problem of inherent brittleness of aerogels and ensures the mechanical strength of the membrane distillation membrane. In addition, the solvent used in the present invention is only alcohol and water, there is no solvent replacement and other complicated pretreatment steps before drying, and the preparation process is very green and convenient.

One aspect of the present invention provides an aerogel composite membrane, including a non-woven support layer and an aerogel filling layer, the aerogel composite membrane has a multi-level hole structure, including sub-micron/micron with a pore size of 0.5-20 μm Nanoscale pores and nanoscale pores with pore diameters ranging from 2 to 100 nm.

In some embodiments, the thickness of the aerogel composite film is 0.1-1 mm, preferably, the thickness of the aerogel composite film is 0.3-0.6 mm.

In some specific embodiments, the hydrophobic angle of the aerogel composite film is 130°-160°, preferably, the hydrophobic angle of the aerogel composite film is 150°-160°.

In some specific embodiments, the thermal conductivity of the aerogel composite film is 0.02-0.05 W·K ⁻¹ ·m ⁻¹ .

In the present invention, the non-woven fabric in the aerogel composite membrane plays a supporting role, the aerogel is filled in its pores, and the filled aerogel has a multi-level pore structure, including submicron/micron with a pore size of 0.5-20 μm. Nano-scale holes and nano-scale holes with a pore size of 2-100nm, among which, sub-micron/micron-scale holes not only provide water vapor channels, but also ensure the thermal insulation performance of composite membranes together with nano-scale holes. In addition, the thickness of the aerogel composite membrane will significantly affect the water vapor transmission resistance in the membrane distillation process, so reducing the thickness of the membrane will help to improve the water flux, however, the thickness of the membrane is too thin, which will reduce the mechanical properties and thermal insulation of the membrane. performance and service life. Therefore, in order to balance the water flux of the membrane, the mechanical properties of the membrane and the thermal insulation performance of the membrane, the thickness of the aerogel composite membrane disclosed in the present invention is controlled between 0.1-1 mm, preferably between 0.3-0.6 mm.

In some specific embodiments, the pore size of the submicron/micron pores is 0.5-20 μm.

In some specific embodiments, the pore size of the nano-scale pores is 2-100 nm.

In some specific embodiments, the hydrophobic angle of the aerogel composite membrane is 130°-160°.

In some embodiments, the nonwoven fabric is a hydrophobic nonwoven fabric.

In some specific embodiments, the non-woven fabric preferably includes PP non-woven fabric, PET non-woven fabric, PTFE non-woven fabric, PP/PET non-woven fabric, PTFE/PP non-woven fabric, PTFE/PET non-woven fabric one or more of.

In some embodiments, the aerogel is a silicon aerogel, preferably a silica aerogel.

Another aspect of the present invention also provides a method for preparing an aerogel composite membrane, comprising:

1) prepare a sol solution comprising alkoxysilane, alcohol and water;

2) immersing the non-woven fabric in the sol solution, taking it out and placing it in a mold to stand, aging treatment, and then drying to obtain the superhydrophobic low thermal conductivity aerogel composite film;

Wherein, the relative pressure of the composite film in the mold during the standing and aging treatment is 1-400Pa, preferably 50-200Pa, more preferably 80-120Pa.

In some embodiments, the mass ratio of the 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 the 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 the step 1) is alkoxysilane: alcohol: water=1:2.5:1.5.

In some embodiments, the alkoxysilane includes methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane, dimethyldiethylsilane One or more of oxysilane and trimethylethoxysilane.

In some preferred embodiments, the alkoxysilane is methyltriethoxysilane.

In some embodiments, the alcohol includes one or more of methanol, ethanol, isopropanol, ethylene glycol, and propylene glycol.

In some preferred embodiments, the alcohol is ethanol.

In some embodiments, the nonwoven fabric is a hydrophobic nonwoven fabric.

In some embodiments, the step 1) includes:

1A) mixing alkoxysilane with alcohol and water to obtain a sol solution;

1B) Adjust the pH value of the sol solution to 9-10.

In some specific embodiments, in the step 1A), the alkoxysilane is mixed with alcohol and water, and the stirring time is 10-40 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 stirred at a temperature of 0-90° C. for 0.5-5 hours to obtain .

In some embodiments, the step 2) includes:

2A) Immerse the non-woven fabric in the sol solution, so that the sol solution is fully filled in the pores and surfaces of the non-woven fabric, take out the dipped non-woven fabric, place it in a mold and let it stand to form a glue, and age to obtain a wet solution. membrane;

2B) Drying the wet film to obtain the superhydrophobic and low thermal conductivity aerogel composite film.

In some specific embodiments, the mold in the step 2A) is a closed container, which can ensure that water and alcohol will not volatilize during the gelation process.

In some specific embodiments, the mold in the step 2A) is a closed flat mold, and its material is plexiglass, glass, stainless steel, ceramics, PP (polyethylene), PE (polypropylene), PVC (polyvinyl chloride) ), one or more of ABS (acrylonitrile/butadiene/styrene copolymer).

In some preferred embodiments, the material of the mold is glass.

In some specific embodiments, the aging temperature in the step 2A) is 25-90° C., and the time is 1-24 hours.

In some specific embodiments, the drying in the step 2B) is normal pressure drying, the drying temperature is 50-90° C., and the drying time is 1-24 hours.

Another aspect of the present invention also provides an aerogel composite membrane prepared by the method according to the second aspect.

In some embodiments, the aerogel composite membrane includes a non-woven support layer and an aerogel filling layer, and has a multi-level pore structure, including submicron/micron pores with a pore size of 0.5-20 μm and a pore size of 2- 100nm nanoscale holes.

Another aspect of the present invention also provides the application of the aerogel composite membrane described in the first aspect or the aerogel composite membrane prepared by the preparation method described in the second aspect in membrane distillation.

The invention provides a super-hydrophobic and low thermal conductivity aerogel composite film, which comprises a non-woven support layer and an aerogel filling layer. The thickness of the aerogel composite film is 0.1-1 mm, and there is no The woven fabric plays a supporting role, and the aerogel is filled in its pores. The filled aerogel has a multi-level pore structure, including sub-micron/micron pores with a pore size of 0.5-20 μm and nano-scale pores with a pore size of 2-100 nm. , wherein, the sub-micron/micron-scale holes not only provide water vapor channels, but also jointly ensure the thermal insulation performance of the composite film with the nano-scale holes, so that the water flux of the superhydrophobic and low thermal conductivity aerogel composite film obtained by the present invention can reach 12.2LMH(L·m ^-2 ·h ^-1 ), the salt cutoff is higher than 99.9%, the hydrophobic angle is as high as 152°, and the thermal conductivity is as low as 0.04W·m ^-1 ·K ^-1 . And a preparation method of the above-mentioned membrane is provided, and the obtained aerogel composite membrane has excellent mechanical properties, good hydrophobicity, good heat resistance and heat insulation properties, and can be applied to the membrane distillation technology to treat seawater, high temperature, etc. Salt water and other processes. In the preparation method of the present invention, only water and alcohol are used as solvents, the aging and drying steps are carried out in an oven, and solvent replacement is not used in the subsequent processing steps, which avoids the large use of organic solvents, reduces the difficulty of waste liquid treatment, and increases It is green and environmentally friendly, and the obtained superhydrophobic and low thermal conductivity aerogel composite film can be further modified with surface functions to meet different needs.

Description of drawings

1 is a scanning electron microscope image of the superhydrophobic and low thermal conductivity aerogel composite film prepared in Example 1.

FIG. 2 is a water contact angle diagram of the superhydrophobic and low thermal conductivity aerogel composite film prepared in Example 1. FIG.

Fig. 3 is the stress-strain curve diagram of the superhydrophobic and low thermal conductivity aerogel composite film prepared in Example 1

4 is a thermal conductivity diagram of the superhydrophobic and low thermal conductivity aerogel composite film prepared in Example 1 and a commercial hydrophobic film.

FIG. 5 is a pore size distribution diagram of the superhydrophobic and low thermal conductivity aerogel composite membrane prepared in Example 1. FIG.

6 is a graph showing the test results of the water flux and salt interception measured by the direct contact membrane distillation method for the superhydrophobic and low thermal conductivity aerogel composite membrane prepared in Example 1.

FIG. 7 is a graph showing the test results of the membrane CM-L prepared in Comparative Example 2 for the water flux measured by the direct contact membrane distillation method.

detailed description

In order to make the present invention easier to understand, the present invention will be described in detail below with reference to the embodiments, which are only for illustrative purposes and do not limit the scope of application of the present invention.

Unless otherwise specified, the operations and treatment methods involved in the present invention belong to conventional methods in the art, the instruments used in the present invention are conventional instruments in the art, and the chemicals used in the present invention can be obtained commercially.

The detection method involved in the specific embodiment of the present invention is as follows:

Scanning electron microscope adopts Japan Hitachi S-4800 scanning electron microscope;

The water contact angle and sliding angle were measured by a water contact angle meter (Precise Test, China);

The stress-strain curve was measured by a universal material testing machine (Kaiqiangli KD-II 10/100N, China)

Thermal conductivity was measured by thermal conductivity meter (Hot-Disk, TPS 2500S, Switzerland);

The pore size distribution of the composite membrane was measured by a mercury porosimeter (AutoPore Iv 9510, USA);

Commercial hydrophobic membranes are PVDF membranes (HVSP, Millipore) with a thickness of 0.098 mm.

Example 1

Mix methyltriethoxysilane with ethanol and water in a mass ratio of 1:2.5:1.5, and stir at room temperature for 24 hours to obtain a sol solution with uniform properties; then, add ammonia water to adjust the pH of the sol solution to 9-10 , stir for 1 hour; immerse the PP non-woven fabric (thickness about 0.45mm) in the sol solution after adjusting the pH, take it out and place it in the glass plate mold and control the relative pressure to be 100Pa, let stand for 10 hours, and then transfer to Aged in a 50°C oven for 5 hours to obtain a wet film; finally, the wet film was taken out of the mold and placed in an 80°C oven to dry for 1 hour to obtain a superhydrophobic and low thermal conductivity aerogel composite film.

The average thickness of the aerogel composite film is 0.48mm, and its microscopic surface morphology is shown in Figure 1. The silica particles formed by the sol-gel are stacked in the pores of the non-woven fabric to form a three-dimensional rich in pores. grid. The water contact angle of the aerogel composite membrane is as high as 152° (Fig. 2), the sliding angle is as low as 6.5°, reaching the superhydrophobic level, and it has excellent mechanical properties (Fig. 3). The transmembrane heat loss in the membrane distillation process is mainly caused by the heat conduction through the membrane, and the conduction heat through the membrane

where λ is the thermal conductivity of the membrane, δ is the thickness of the membrane, and T _f,m and T _p,m are the average temperatures of the membrane surface on the feed side and the membrane surface on the permeate side, respectively. When the membrane surface temperature conditions are the same, λ/δ is the main factor that determines the membrane conduction heat flux. The thermal conductivity test of the aerogel composite film shows that (Fig. 4), compared with the commercial hydrophobic film, the thermal conductivity of the aerogel composite film is 62.1% of the commercial film, and the thickness is about 5 times that of the commercial film. Therefore, under the same temperature difference, the conduction heat loss of the aerogel composite membrane is only 12.5% of that of the commercial membrane, which greatly improves the thermal efficiency of the membrane distillation process. In addition, the pore sizes of the pores of the composite membrane are 6-15 μm and 10-1000 nm (Fig. 5).

Example 2

Mix methyltrimethoxysilane with ethanol and water in a mass ratio of 1:2.5:1.5, and stir at room temperature for 24 hours to obtain a sol solution with uniform properties; then, add ammonia water to adjust the pH of the sol solution to 9-10, and stir 1 hour; immerse the PP non-woven fabric in the sol solution after adjusting the pH, take it out and place it in a glass flat mold and control the relative pressure to 100Pa, let it stand for 10 hours, and then transfer it to a 50°C oven for aging for 5 hours. A wet film was obtained; finally, the wet film was taken out of the mold and dried in an oven at 80° C. for 1 hour to obtain a superhydrophobic and low thermal conductivity aerogel composite film. The hydrophobic angle of the aerogel composite film is 154°, the sliding angle is 8°, and the thermal conductivity is 0.035W·K ^-1 ·m ^-1 .

Example 3

Mix methyltriethoxysilane with ethanol and water in a mass ratio of 1:2.5:1.5, and stir at room temperature for 24 hours to obtain a sol solution with uniform properties; then, add ammonia water to adjust the pH of the sol solution to 9-10, Stir for 1 hour; immerse the PTFE/PP non-woven fabric in the pH-adjusted sol solution, take it out and place it in a glass flat mold and control the relative pressure to 100Pa, let stand for 10 hours, and then transfer to a 50°C oven for aging After 5 hours, a wet film was prepared; finally, the wet film was taken out from the mold and placed in an oven at 80° C. to be dried for 1 hour to obtain a hydrophobic and low thermal conductivity aerogel composite film. The hydrophobic angle of the aerogel composite film is 140°, the sliding angle is 28°, and the thermal conductivity is 0.053 W·K ^-1 ·m ^-1 .

Example 4

Methyltriethoxysilane, dimethyldiethoxysilane, ethanol and water were mixed in a mass ratio of 0.8:0.2:2.5:1.5, and stirred at room temperature for 24 hours to obtain a sol liquid with uniform properties; then, ammonia water was added Adjust the pH value of the sol solution to 9-10, and stir for 1 hour; immerse the PP non-woven fabric in the pH-adjusted sol solution, take it out and place it in a glass plate mold and control the relative pressure to be 100 Pa, and let it stand for 10 hours. Then, it was transferred to a 50°C oven for 5 hours to obtain a wet film; finally, the wet film was taken out of the mold and placed in an 80°C oven to dry for 1 hour to obtain a hydrophobic and low thermal conductivity aerogel composite film. The hydrophobic angle of the aerogel composite film is 145°, the sliding angle is 25°, and the thermal conductivity is 0.051 W·K ^-1 ·m ^-1 .

Example 5

Mix methyltrimethoxysilane with methanol and water in a mass ratio of 1:2.5:1.5, and stir at room temperature for 24 hours to obtain a sol solution with uniform properties; then, add ammonia water to adjust the pH of the sol solution to 9-10, and stir 1 hour; immerse the PP non-woven fabric in the sol solution after adjusting the pH, take it out and place it in a glass flat mold and control the relative pressure to 100Pa, let it stand for 10 hours, and then transfer it to a 50°C oven for aging for 5 hours. A wet film was obtained; finally, the wet film was taken out of the mold and dried in an oven at 80° C. for 1 hour to obtain a superhydrophobic and low thermal conductivity aerogel composite film. The hydrophobic angle of the aerogel composite film is 154°, the sliding angle is 6°, and the thermal conductivity is 0.035W·K ^-1 ·m ^-1 .

Example 6

Mix methyltriethoxysilane with ethanol and water in a mass ratio of 1:2.5:1.5, and stir at room temperature for 24 hours to obtain a sol solution with uniform properties; then, add ammonia water to adjust the pH of the sol solution to 9-10, Stir for 1 hour; immerse the PP non-woven fabric in the sol solution after adjusting the pH, take it out and place it in a glass flat mold and control the relative pressure to 100Pa, let it stand for 5 hours, and then transfer it to a 50°C oven for aging for 5 hours , to obtain a wet film; finally, the wet film was taken out of the mold and dried in an oven at 80° C. for 1 hour to obtain a hydrophobic and low thermal conductivity aerogel composite film. The hydrophobic angle of the aerogel composite film is 140°, the sliding angle is 16°, and the thermal conductivity is 0.051W·K ^-1 ·m ^-1 .

Example 7

Mix methyltriethoxysilane with ethanol and water in a mass ratio of 0.7:2.5:1.5, and stir at room temperature for 24 hours to obtain a sol solution with uniform properties; then, add ammonia water to adjust the pH of the sol solution to 9-10, and stir 1 hour; immerse the PP non-woven fabric in the sol solution after adjusting the pH, take it out and place it in a ceramic flat mold and control the relative pressure to 100Pa, let it stand for 10 hours, and then transfer it to a 50°C oven for aging for 5 hours. A wet film was obtained; finally, the wet film was taken out of the mold and dried in an oven at 80° C. for 1 hour to obtain a superhydrophobic and low thermal conductivity aerogel composite film. The hydrophobic angle of the aerogel composite film is 150°, the sliding angle is 6°, and the thermal conductivity is 0.039 W·K ^-1 ·m ^-1 . .

Application example 1

In order to test the membrane distillation performance of the low thermal conductivity and superhydrophobic aerogel composite membrane prepared in Example 1, 3.5wt% sodium chloride solution was used as the feed solution, deionized water was used as the permeate to test, and the feed was controlled. The temperature of the feed liquid is 60°C, the temperature of the permeate is 20°C, the flow rate in the pipeline is 0.4L/min, and the cross-flow velocity of the water flow on the membrane surface is 6.3cm/s. The water flux is calculated by the mass change of the water on the permeate side, and the salt intercept is calculated by measuring the change in the conductivity of the permeate side. The specific data are shown in Figure 6.

It can be seen from Figure 6 that the superhydrophobic and low thermal conductivity aerogel composite membrane prepared in Example 1 has a high water flux under the test of direct contact membrane distillation, up to 12.2LMH, and its salt cutoff is as high as 99.9%.

Comparative Example 1

Mix methyltriethoxysilane with ethanol and water in a mass ratio of 1:2.5:1.5, and stir at room temperature for 24 hours to obtain a sol solution with uniform properties; then, add ammonia water to adjust the pH of the sol solution to 9-10, Stir for 1 hour; place the PP non-woven fabric on a glass plate, pour the sol solution evenly on the non-woven fabric, use a glass rod to remove excess solution on the membrane surface, and let stand for 10 hours.

Since the solvent is a water-alcohol mixture, it will volatilize rapidly in an open environment and 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

Literature [“Performance of ceramic membrane in vacuum membrane distillation and in vacuum membrane crystallization”, Chia-Chieh Ko et al., Desalination, 440 (2018), pp. 48-58, published on March 30, 2018] reported A preparation method of a porous silica aerogel composite membrane, the details are as follows:

Methyltrimethoxysilane (MTMS) was mixed with ethanol (EtOH) and hydrochloric acid (HCl) in deionized water and stirred at room temperature for 90 minutes to obtain a homogeneous sol. Wherein, the molar ratio of MTMS:EtOH:HCl:deionized water was 1:3:(6.9×10 ⁻⁴ ):1. _{Then, ethanol, ammonia water (NH 3} ·H ₂ O) and deionized water were added in a molar ratio of 1:0.223:2.12, and the mixture was stirred at room temperature for 30 minutes. Subsequently, the alumina tubular membrane was immersed in the sol solution for 1 day to obtain the aerogel composite membrane. After that, the aerogel composite membrane was immersed in ethanol and aged for 2 days, and then the aged aerogel composite membrane was immersed in n-hexane for 1 day of solvent replacement. Finally, the aerogel composite membrane after solvent replacement was dried at room temperature and normal pressure to obtain aerogel composite membrane (CM-L).

Using pure water as the feed liquid, the CM-L membrane was tested for direct contact membrane distillation performance. The temperature of the feed liquid was controlled at about 50°C, and the cross-flow flow in the pipeline was 0.3L/min. Through the change of the water quality on the permeate side, the water flow rate was calculated. 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 Figure 7 that the water flux of the CM-L membrane with the alumina membrane as the support layer was maintained at about 0.6 LMH after 60 minutes, while the It can be seen from Fig. 6 that the water flux of the aerogel composite membrane using the non-woven fabric as the support layer of the present invention can be as high as 12.2 LMH, and it can be seen that the superhydrophobic and low thermal conductivity aerogel composite film prepared by the method of the present invention is selected. Membranes have higher water flux. At the same time, the present invention avoids the solvent replacement step in the preparation process, and is more energy-saving and environmentally friendly.

It should be noted that the above-mentioned embodiments are only used to explain the present invention, and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it is to be understood that the words used therein are words of description and explanation, rather than words of limitation. The present invention may be modified within the scope of the claims of the present invention as specified, and may be modified without departing from the scope and spirit of the present invention. Although the invention described herein refers to the specific methods, materials and embodiments, it is not intended to be limited to the specific examples disclosed therein, but rather, the invention extends to all other methods and applications having the same function.

Claims

An aerogel composite membrane, comprising a non-woven support layer and an aerogel filling layer; wherein, the aerogel composite membrane has a multi-level hole structure, including submicron/micron-scale holes and pore diameters with a pore size of 0.5-20 μm It is a nanoscale hole of 2-100nm.
The aerogel composite membrane according to claim 1, wherein the aerogel composite membrane has a thickness of 0.1-1 mm, preferably a thickness of the aerogel composite membrane is 0.3-0.6 mm.
The aerogel composite film according to claim 1 or 2, wherein the non-woven fabric is a hydrophobic non-woven fabric; preferably, the non-woven fabric includes PP non-woven fabric, PET non-woven fabric, and PTFE non-woven fabric. One or more of woven fabric, PP/PET non-woven fabric, PTFE/PP non-woven fabric, and PTFE/PET non-woven fabric.
The aerogel composite membrane according to claim 1 or 2, wherein the aerogel is silicon aerogel, preferably silica aerogel.
A preparation method of aerogel composite membrane, comprising:

1) prepare a sol solution comprising alkoxysilane, alcohol and water;

2) immersing the non-woven fabric in the sol solution, taking it out and placing it in a mold to stand, aging treatment, and then drying to obtain the superhydrophobic and low thermal conductivity aerogel composite film;

Wherein, the relative pressure of the composite film in the mold during the standing and aging treatment is 1-400Pa, preferably 50-200Pa, more preferably 80-120Pa.
The preparation method according to claim 5, wherein the mass ratio of alkoxysilane, alcohol and water described in step 1) is 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.
The preparation method according to claim 5, wherein the alkoxysilane comprises methyltrimethoxysilane, dimethyldimethoxysilane, trimethylmethoxysilane, methyltriethoxysilane One or more of dimethylsilane, dimethyldiethoxysilane and trimethylethoxysilane, preferably methyltriethoxysilane.
The preparation method according to claim 5, wherein the alcohol comprises one or more of methanol, ethanol, isopropanol, ethylene glycol, and propylene glycol, preferably ethanol.
The preparation method according to claim 5, wherein the non-woven fabric is a hydrophobic non-woven fabric; preferably, the non-woven fabric includes PP non-woven fabric, PET non-woven fabric, PTFE non-woven fabric, PP/ One or more of PET non-woven fabrics, PTFE/PP non-woven fabrics, and PTFE/PET non-woven fabrics.
The preparation method according to any one of claims 5-9, wherein the step 1) comprises:

1A) mixing alkoxysilane with alcohol and water to obtain a sol solution;

1B) Adjust the pH value of the sol solution to 9-10.
The preparation method according to claim 10, wherein in the step 1A), the alkoxysilane is mixed with alcohol and water, and stirred for 10-40 hours to obtain a sol solution.
The preparation method according to claim 10, wherein 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 stirred at a temperature of 0-90°C for 0.5 -5 hours, that's it.
The preparation method according to any one of claims 5-9, wherein the step 2) comprises:

2A) Immerse the non-woven fabric in the sol solution, so that the sol solution is fully filled in the pores and surfaces of the non-woven fabric, take out the dipped non-woven fabric, place it in a mold and let it stand to form a glue, and age to obtain a wet solution. membrane;

2B) Drying the wet film to obtain the superhydrophobic and low thermal conductivity aerogel composite film.
The preparation method according to claim 13, wherein the mold in the step 2A) is a flat mold, preferably a closed flat mold, and its material is plexiglass, glass, stainless steel, ceramics, polyethylene, polypropylene, One or more of polyvinyl chloride and acrylonitrile/butadiene/styrene copolymer, more preferably glass.
The preparation method according to claim 13, wherein the aging temperature in the step 2A) is 25-90° C. and the time is 1-24 hours.
The preparation method according to claim 13, wherein the drying in the step 2B) is normal pressure drying, the drying temperature is 50-100°C, and the drying time is 1-24 hours.
The aerogel composite membrane prepared according to the preparation method of any one of claims 5-16.
The aerogel composite membrane according to claim 17, wherein the aerogel composite membrane has a multi-level pore structure, including submicron/micron pores with a pore size of 0.5-20 μm and pores with a pore size of 2-100 nm. Nanoscale pores.
The aerogel composite membrane according to claim 17 or 18, wherein the aerogel composite membrane has a thickness of 0.1-1 mm, preferably, the aerogel composite membrane has a thickness of 0.3-0.6 mm.
Application of the aerogel composite membrane according to any one of claims 1-4 or the aerogel composite membrane prepared by the preparation method according to any one of claims 5-16 in membrane distillation .