Method for preparing super-hydrophobic silica aerogel by using industrial waste chlorosilane azeotrope

Abstract

The application discloses a method for preparing super-hydrophobic silica aerogel by using industrial waste chlorosilane azeotrope. The method comprises the following steps: providing industrial waste chlorosilane azeotrope, the main components of which include trimethylchlorosilane and silicon tetrachloride; adding the industrial waste chlorosilane azeotrope into a mixture of water and non-alcohol organic solvent to react, obtaining silica sol, and heating the silica sol to obtain silica wet gel through polycondensation reaction; and after solvent replacement and drying, obtaining super-hydrophobic silica aerogel, the hydrophobic angle of which is 150-160 degrees. The raw material of the super-hydrophobic silica aerogel is industrial waste, the process is simple, the cost is low, and the super-hydrophobic silica aerogel is conducive to large-scale industrial production. The super-hydrophobic silica aerogel not only solves the environmental protection problem of industrial waste chlorosilane azeotrope, but also obtains high-value silica aerogel, and has great application prospect in the fields of heat insulation, adsorption, environmental protection and catalysis.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing super-hydrophobic silica aerogel, in particular to a method for preparing super-hydrophobic silica aerogel by using industrial waste chlorosilane azeotrope, and belongs to the technical field of nanomaterials. BACKGROUND

[0002] Aerogel is considered to be the lightest solid in the world, has excellent heat preservation effect, and can even help astronauts resist the cold in space, so it is favored by NASA, the United States National Aeronautics and Space Administration, and is called a "miraculous material changing the world". In the aerogel, the silica aerogel is the most widely used one, which mainly comprises air and has an amorphous SiO2 basic framework, has low thermal conductivity, low density, high porosity, high light transmittance, high specific surface area, low refractive index and low sound speed, and has unique performance in mechanics, thermotics, electricity, optics and acoustics, thereby having wide application prospects in many fields.

[0003] At present, the raw materials for preparing the silica aerogel mainly include organosiloxane and silicate. For example, patent CN109850909A discloses a method for preparing super-hydrophobic silica aerogel at normal pressure, organosiloxane, anhydrous ethanol and water are mixed to obtain a mixed solution, the pH value is adjusted to 2-3, DMF is added and the pH value of the reaction solution is adjusted to 5-6, the gel is formed after standing, the gel is modified by using a mixed solution of hexamethylenetetramine, DMF and ethanol, and finally the super-hydrophobic SiO2 aerogel is obtained by drying at normal pressure. Patent CN109052415A discloses a silica aerogel based on MTMS and a preparation method thereof, deionized water and cetyltrimethylammonium bromide are mixed, then methyltrimethoxysilane is added, ammonia water is added after constant temperature stirring, the wet gel is washed and dried to obtain super-hydrophobic silica aerogel. Patent CN105731470A discloses a preparation method of silica aerogel composite material, a surfactant, methanol and acetic acid solution are mixed and stirred to dissolve the surfactant, then DMF, MTMS and DMDMS are added, the solution is hydrolyzed in a constant temperature magnetic stirrer, then an alkali solution is added to adjust the pH value so that the solution forms a gel, and the elastic super-hydrophobic aerogel is prepared through aging, solvent replacement and normal pressure drying. The organosiloxane precursor can be used to prepare high-quality silica aerogel, but the cost of the organosiloxane raw material is too high, which hinders the large-scale use of the silica aerogel.

[0004] Patent CN106430219A discloses a method for preparing silica aerogel at low cost, using cheap industrial water glass as precursor, water as reaction solvent, and oxalic acid as acidic catalyst. The silica aerogel is prepared by normal pressure drying process. Patent CN101844771A discloses a method for preparing super-hydrophobic silica aerogel under normal pressure, by adding first surface modifier, second surface modifier, non-polar organic solvent and inorganic acid to water glass solution and reacting to prepare hydrophobic silica wet gel, and washing and drying the hydrophobic silica wet gel to obtain super-hydrophobic silica aerogel. Although silica aerogel can be synthesized using cheap water glass as silicon source, the silica aerogel prepared by this method must be subjected to hydrophobic modification treatment, otherwise the nano-porous structure of the silica aerogel will gradually absorb water, causing the collapse of the three-dimensional nano-skeleton, and the porosity, specific surface area and pore volume of the aerogel will decrease sharply, and the excellent adsorption, catalysis and heat insulation properties will no longer exist. The use of hydrophobic reagent modification can obtain super-hydrophobic silica gel without affecting the structure of the silica aerogel, but the process flow of this method is complex, requires multiple solvent replacement, has long cycle and high cost.

[0005] Therefore, it is of great significance to synthesize super-hydrophobic silica aerogel by cheap raw materials, quickly and at low cost.

[0006] In the synthesis process of organosilicon monomers, a by-product is a azeotrope composed of trimethyl monochlorosilane and silicon tetrachloride. Among them, the boiling point of trimethyl monochlorosilane is 57.7℃, and the boiling point of tetrachlorosilane is 57.6℃. The content of trimethyl monochlorosilane in the azeotrope is about 45-60wt%, and the content of silicon tetrachloride is about 30-50wt%. According to the current domestic production process route and level of methyl chlorosilane, the mass fraction of azeotrope is about 1-2wt% of the crude monomer product. That is, for every 10,000 tons of organosilicon monomers produced, at least 100 tons of azeotrope will be produced. In 2021, the output of organosilicon reached 3.06 million tons, an increase of 15.9% year-on-year, about 306 tons. Chlorosilane azeotrope is flammable, irritating and corrosive, if not converted and utilized in time, it will not only cause resource waste, but also cause great safety and environmental protection hidden dangers.

[0007] If the chlorosilane azeotrope can be converted into high value-added silica aerogel, both the harm of chlorosilane azeotrope to the environment and the preparation of silica aerogel can be solved, and the trimethyl monochlorosilane in the chlorosilane azeotrope is an excellent hydrophobic modification reagent, which can directly modify the gel during the preparation process to quickly prepare super-hydrophobic silica aerogel. Patent 98811584.0 discloses a method for producing silicon tetrachloride-based and organically modified aerogel. The invention obtains a hydrogel by directly reacting silicon tetrachloride with water, and then performs surface modification on the obtained hydrogel to obtain a surface-modified hydrogel. The patent uses cheap silicon tetrachloride as a silicon source, but needs a complicated surface modification step, which is not conducive to the large-scale production of silica aerogel. SUMMARY

[0008] The main purpose of the present application is to provide a method for preparing super-hydrophobic silica aerogel using industrial waste chlorosilane azeotrope, which solves the technical problems of high cost, long cycle and complex surface modification process in the prior art, and the safety and environmental protection problems caused by industrial waste chlorosilane azeotrope.

[0009] To achieve the above-mentioned purposes, the technical scheme adopted by the present application comprises:

[0010] The embodiment of the present application provides a method for preparing super-hydrophobic silica aerogel using industrial waste chlorosilane azeotrope, which comprises:

[0011] Providing industrial waste chlorosilane azeotrope, the main components of the industrial waste chlorosilane azeotrope include trimethyl chlorosilane and silicon tetrachloride, wherein the mole percentage of trimethyl chlorosilane is 20-50%, and the mole percentage of silicon tetrachloride is 50-80%;

[0012] Adding the industrial waste chlorosilane azeotrope into a mixture of water and a non-alcohol organic solvent to react, to obtain a silica sol, wherein the mole ratio of the non-alcohol organic solvent to the industrial waste chlorosilane azeotrope is 0.1-5:1;

[0013] Heating the silica sol to obtain a silica wet gel through polycondensation reaction;

[0014] Performing solvent replacement on the silica wet gel to obtain a silica gel, and then performing drying treatment to obtain super-hydrophobic silica aerogel.

[0015] In some embodiments, the non-alcohol organic solvent includes any one or a combination of two or more of tetrahydrofuran, butanone, acetonitrile, dimethyl sulfoxide, n-hexane, n-heptane, etc.

[0016] Compared with the prior art, the present application has at least the following advantages:

[0017] 1) The super-hydrophobic silica aerogel provided by the present application is prepared from industrial waste chlorosilane azeotrope, and the cost of the silica source is almost 0, and the safety and environmental protection problems caused by the industrial waste chlorosilane azeotrope can be solved;

[0018] 2) The super-hydrophobic silica aerogel provided by the present application has super-hydrophobicity without a hydrophobic modification process, and the hydrophobic angle is 150-160°;

[0019] 3) The preparation method of the super-hydrophobic silica aerogel provided by the present application is simple, low in cost, short in period, and conducive to large-scale industrial production, and can solve the technical problems of high preparation cost, long period and complex surface modification process of the super-hydrophobic silica aerogel in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0021] Figure 1 is a schematic diagram of a method for preparing super-hydrophobic silica aerogel by using industrial waste chlorosilane azeotrope in a typical embodiment of the present application;

[0022] Figure 2 is a nitrogen adsorption-desorption curve diagram of the super-hydrophobic silica aerogel obtained in Example 1 of the present application;

[0023] Figure 3 is a pore size distribution diagram of the super-hydrophobic silica aerogel obtained in Example 1 of the present application;

[0024] Figure 4 is a scanning electron microscope photograph of the super-hydrophobic silica aerogel obtained in Example 1 of the present application;

[0025] Figure 5 is a transmission electron microscope photograph of the super-hydrophobic silica aerogel obtained in Example 1 of the present application;

[0026] Figure 6 is a contact angle diagram of the super-hydrophobic silica aerogel obtained in Example 1 of the present application;

[0027] Figure 7 is a scanning electron microscope photograph of the super-hydrophobic silica aerogel obtained in Example 2 of the present application;

[0028] Figure 8 is a transmission electron microscope photograph of the super-hydrophobic silica aerogel obtained in Example 2 of the present application;

[0029] Figure 9 is a TG curve diagram of the super-hydrophobic silica aerogel obtained in Example 2 of the present application;

[0030] Figure 10 is a contact angle diagram of the super-hydrophobic silica aerogel obtained in Example 2 of the present application. DETAILED DESCRIPTION

[0031] In view of the deficiencies in the prior art, the present inventors have, through long-term research and a large number of practices, come up with the technical solution of the present application, which is mainly to obtain a silica gel through hydrolysis and polycondensation reaction of industrial waste chlorosilane azeotrope, and then obtain a super-hydrophobic silica aerogel through solvent replacement and drying steps. The technical solution, its implementation process and principles will be further explained as follows.

[0032] One aspect of the present application provides a method for preparing a super-hydrophobic silica aerogel using industrial waste chlorosilane azeotrope, which comprises:

[0033] adding the industrial waste chlorosilane azeotrope into a mixture of water and a non-alcohol organic solvent to react, to obtain a silica sol;

[0034] heating the silica sol to obtain a silica wet gel through polycondensation reaction;

[0035] performing solvent replacement on the silica wet gel and then drying to obtain a super-hydrophobic silica aerogel.

[0036] Please refer to Figure 1 As shown in the figure, the method for preparing a super-hydrophobic silica aerogel using industrial waste chlorosilane azeotrope comprises the following steps:

[0037] 1) adding the industrial waste chlorosilane azeotrope into a mixture of water and a non-alcohol organic solvent at a certain temperature to react, to obtain a silica sol;

[0038] 2) heating the silica sol obtained in step 1) at a certain temperature to obtain a silica wet gel through polycondensation reaction;

[0039] 3) performing solvent replacement on the silica wet gel obtained in step 2) and then drying at normal pressure or special drying to obtain a super-hydrophobic silica aerogel.

[0040] In some embodiments, the main components of the industrial waste chlorosilane azeotrope include trimethylchlorosilane and silicon tetrachloride, wherein the mole percentage of trimethylchlorosilane is 20-50%, and the mole percentage of silicon tetrachloride is 50-80%. Trimethylchlorosilane in the industrial waste chlorosilane azeotrope is not only a silicon source but also an excellent hydrophobic modification reagent, which can directly modify the gel during preparation to quickly prepare superhydrophobic silica aerogel. The entire superhydrophobic silica aerogel preparation process, technology and cycle are greatly optimized, the comprehensive cost is low, and it is conducive to large-scale production.

[0041] Further, the industrial waste chlorosilane azeotrope is derived from by-products in the production of industrial organosilicon monomers or by-products in the production of industrial single crystal silicon, and is not limited thereto.

[0042] In some embodiments, step 1) comprises: adding the industrial waste chlorosilane azeotrope dropwise to a mixture of water and a non-alcohol organic solvent at a first temperature to obtain a silica sol. The first temperature is 5-25°C, preferably 10-20°C.

[0043] In some embodiments, in step 1), the dropwise addition speed of the industrial waste chlorosilane azeotrope is 0.001-10 L / min, preferably 0.01-0.1 L / min.

[0044] In some embodiments, in step 1), the non-alcohol organic solvent includes any one or a combination of two or more of tetrahydrofuran, butanone, acetonitrile, dimethyl sulfoxide, n-hexane, n-heptane, etc., and is not limited thereto. The industrial waste chlorosilane azeotrope of the present application does not undergo a silicon esterification process through an alcohol organic solvent in the hydrolysis process, and directly generates a silicon hydroxyl group.

[0045] In some embodiments, in step 1), the molar ratio of the non-alcohol organic solvent to the industrial waste chlorosilane azeotrope is 0.1-5:1, preferably 1-4:1.

[0046] In some embodiments, in step 1), the molar ratio of water to the industrial waste chlorosilane azeotrope is 1-5:1, preferably 2-4:1.

[0047] In some embodiments, step 2) comprises: heating the silica sol to a second temperature to obtain a silica wet gel through a polycondensation reaction; and the second temperature is 25-80°C, preferably 40-60°C. The present application uses hydrochloric acid generated by the chlorosilane azeotrope itself for acid catalysis one-step gelation in the polycondensation reaction during the gelation process, and does not need to add additional acid or base catalysts, so the sol-gel preparation process is simple.

[0048] Further, in step 2), the heating time is 1-48 hours, preferably 6-24 hours.

[0049] In some embodiments, step 3) comprises: first performing solvent replacement on the silica wet gel to obtain a silica gel, and then performing drying treatment to obtain the super-hydrophobic silica aerogel, wherein the replacement solvent used in the solvent replacement comprises any one or a combination of two or more of water, t-butyl alcohol, ethanol, acetone, n-hexane, tetrahydrofuran, dimethyl sulfoxide, and the like, and is not limited thereto.

[0050] Further, the number of times of the solvent replacement is 0-10, preferably 3-6.

[0051] In some embodiments, in step 3), the drying treatment comprises normal pressure drying, or special drying, and the like, but is not limited thereto.

[0052] Further, the temperature of the normal pressure drying is 20-200℃, preferably 60-100℃, and the time of the normal pressure drying is 1-24h.

[0053] In other embodiments, step 3) comprises: performing special drying treatment on the silica gel, wherein the drying comprises any one or a combination of two of vacuum drying and supercritical drying, and is not limited thereto.

[0054] Further, the vacuum drying comprises freeze vacuum drying and / or normal temperature vacuum drying, wherein the cold trap temperature of the freeze vacuum drying is -45--80℃, and the drying time is 6-48h.

[0055] Further, the supercritical fluid used in the supercritical drying comprises any one of supercritical CO2, supercritical ethanol, and the like, and the supercritical drying specifically can comprise: using the supercritical fluid to replace the liquid component inside the gel material in a supercritical environment of a specific supercritical fluid, and the drying time is 6-48h.

[0056] Another aspect of the embodiments of the present application also provides the super-hydrophobic silica aerogel prepared by the foregoing method.

[0057] Further, the super-hydrophobic silica aerogel is composed of a three-dimensional porous network structure formed by mutual connection of silica nanoparticles, and the three-dimensional porous network structure comprises micropores with a pore size of less than 2nm, mesopores with a pore size of 2-50nm, and macropores with a pore size of 50nm-50μm.

[0058] Further, the super-hydrophobic silica aerogel has super-hydrophobicity, and the hydrophobic angle thereof is 150-160°.

[0059] In some embodiments, the density of the super-hydrophobic silica aerogel is 20-300mg / cm 3 , preferably 60-150mg / cm3 .

[0060] Further, the specific surface area of the superhydrophobic silica aerogel is 100-1200 m 2 / g, preferably 400-800 m 2 / g.

[0061] Further, the pore volume of the superhydrophobic silica aerogel is 0.5-4 cm 3 / g, preferably 1-3 cm 3 / g.

[0062] Further, the porosity of the superhydrophobic silica aerogel is 80-99%, preferably 85-98%.

[0063] Further, the thermal conductivity of the superhydrophobic silica aerogel is 0.015-0.04 W / (m·K), preferably 0.018-0.03 W / (m·K).

[0064] In summary, the present application uses industrial waste chlorosilane azeotrope as a silicon source, and the cost of the silicon source is almost zero. Not only can the safety and environmental protection problems caused by waste chlorosilane azeotrope be solved, but also high-value silica aerogel is obtained, which has great application prospects in the fields of thermal insulation, adsorption, environmental protection and catalysis. Moreover, the polycondensation reaction in the gel process of the present application uses hydrochloric acid generated by the chlorosilane azeotrope itself, and no additional acid or base catalyst needs to be added, so the sol-gel preparation process is simple. Trimethylchlorosilane in the industrial waste chlorosilane azeotrope is not only a silicon source, but also an excellent hydrophobic modification reagent, which can directly modify the gel during preparation to quickly prepare superhydrophobic silica aerogel. The entire superhydrophobic silica aerogel preparation process, technology and cycle are greatly optimized, the comprehensive cost is low, and it is conducive to large-scale production.

[0065] The technical solutions of the present application will be described in further detail below in conjunction with several preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application. The experimental methods not specified in the following embodiments are usually carried out according to the conventional conditions or the conditions suggested by the manufacturers.

[0066] Example 1

[0067] (1) The industrial waste chlorosilane azeotrope was added dropwise into a mixed solvent of tetrahydrofuran and water at 5°C to obtain a silica sol. The molar percentage of trimethylchlorosilane in the chlorosilane azeotrope was 20%, and the molar percentage of silicon tetrachloride was 80%. The molar ratio of the chlorosilane azeotrope, tetrahydrofuran and water was 1:1:2, and the dropwise rate was 0.1 L / min.

[0068] (2) The silica sol obtained in step 1) was heated to obtain a silica wet gel through a polycondensation reaction. The heating time was 6 h, and the temperature was 60°C.

[0069] (3) The silica wet gel obtained in step 2) was replaced with ethanol solvent for 6 times and then dried at normal pressure. The drying temperature was 80°C, and the drying time was 24 h to obtain a superhydrophobic silica aerogel.

[0070] The nitrogen adsorption and desorption curve of the superhydrophobic silica aerogel obtained in this example is shown in Figure 2 , the pore size distribution is shown in Figure 3 , the SEM structure is shown in Figure 4 , the TEM image is shown in Figure 5 , and the contact angle is shown in Figure 6 . The specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica aerogel obtained in this example are shown in Table 1.

[0071] Example 2

[0072] (1) The industrial waste chlorosilane azeotrope was added dropwise into a mixed solvent of acetonitrile and water at 5°C to obtain a silica sol. The molar percentage of trimethylchlorosilane in the chlorosilane azeotrope was 20%, and the molar percentage of silicon tetrachloride was 80%. The molar ratio of the chlorosilane azeotrope, acetonitrile and water was 1:0.1:4, and the dropwise rate was 0.001 L / min.

[0073] (2) The silica sol obtained in step 1) was heated to obtain a silica wet gel through a polycondensation reaction. The heating time was 24 h, and the temperature was 50°C.

[0074] (3) The silica wet gel obtained in step 2) was replaced with acetone and n-hexane solvent for 10 times and then dried at normal pressure. The drying temperature was 60°C, and the drying time was 1 h to obtain a superhydrophobic silica aerogel.

[0075] The SEM structure of the superhydrophobic silica aerogel obtained in this example is shown in Figure 7 , the TEM image is shown in Figure 8 , the thermogravimetric analysis diagram is shown in Figure 9 , and the contact angle is shown in Figure 10 . The specific surface area, hydrophobic angle, pore volume and density of the superhydrophobic silica aerogel obtained in this example are shown in Table 1.

[0076] Example 3

[0077] (1) At 25℃, the industrial waste chlorosilane azeotrope was added dropwise into the mixed solvent of methyl ethyl ketone and water to obtain a silica sol. The molar percentage of trimethylchlorosilane in the chlorosilane azeotrope was 50%, and the molar percentage of silicon tetrachloride was 50%. The molar ratio of chlorosilane azeotrope, methyl ethyl ketone and water was 1:5:1, and the dropwise rate was 1 L / min.

[0078] (2) The silica sol obtained in step 1) was heated to obtain a silica wet gel through polycondensation reaction. The heating time was 1 h, and the temperature was 80℃.

[0079] (3) The silica wet gel obtained in step 2) was replaced once with tetrahydrofuran solvent and then dried at normal pressure. The drying temperature was 20℃, and the drying time was 6 h to obtain a superhydrophobic silica aerogel.

[0080] The physical parameters of the superhydrophobic silica aerogel obtained in this example, such as specific surface area, hydrophobic angle, pore volume and density, can be seen in Table 1.

[0081] Example 4

[0082] (1) At 15℃, the industrial waste chlorosilane azeotrope was added dropwise into the mixed solvent of dimethyl sulfoxide and water to obtain a silica sol. The molar percentage of trimethylchlorosilane in the chlorosilane azeotrope was 30%, and the molar percentage of silicon tetrachloride was 70%. The molar ratio of chlorosilane azeotrope, dimethyl sulfoxide and water was 1:2:2.5, and the dropwise rate was 0.5 L / min.

[0083] (2) The silica sol obtained in step 1) was heated to obtain a silica wet gel through polycondensation reaction. The heating time was 6 h, and the temperature was 80℃.

[0084] (3) The silica wet gel obtained in step 2) was replaced three times with dimethyl sulfoxide solvent and then dried at normal pressure. The drying temperature was 200℃, and the drying time was 6 h to obtain a superhydrophobic silica aerogel.

[0085] The physical parameters of the superhydrophobic silica aerogel obtained in this example, such as specific surface area, hydrophobic angle, pore volume and density, can be seen in Table 1.

[0086] Example 5

[0087] (1) At 15℃, the industrial waste chlorosilane azeotrope was added dropwise into the mixed solvent of dimethyl sulfoxide and water to obtain a silica sol. The molar percentage of trimethylchlorosilane in the chlorosilane azeotrope was 30%, and the molar percentage of silicon tetrachloride was 70%. The molar ratio of chlorosilane azeotrope, dimethyl sulfoxide and water was 1:2:2.5, and the dropwise rate was 0.5 L / min.

[0088] (2) The silica sol obtained in step 1) is heated to obtain silica wet gel through polycondensation reaction. The heating time is 48 h and the temperature is 25 °C.

[0089] (3) The silica wet gel obtained in step 2) is freeze-dried after being replaced with water and t-butyl alcohol solvent for 3 times. The cold trap temperature is -80 °C and the drying time is 6 h to obtain super-hydrophobic silica aerogel.

[0090] The physical parameters of the super-hydrophobic silica aerogel obtained in this example, such as specific surface area, hydrophobic angle, pore volume and density, can be seen in Table 1.

[0091] Example 6

[0092] (1) The industrial waste chlorosilane azeotrope is added dropwise into a mixture of n-heptane and water at 15 °C to obtain silica sol. The molar percentage of trimethylchlorosilane in the chlorosilane azeotrope is 35%, and the molar percentage of silicon tetrachloride is 65%. The molar ratio of chlorosilane azeotrope, n-heptane and water is 1:3:2, and the dropwise rate is 0.5 L / min.

[0093] (2) The silica sol obtained in step 1) is heated to obtain silica wet gel through polycondensation reaction. The heating time is 24 h and the temperature is 40 °C.

[0094] (3) The silica wet gel obtained in step 2) is dried with supercritical CO2 after being replaced with ethanol solvent for 3 times. The drying time is 48 h to obtain super-hydrophobic silica aerogel.

[0095] The physical parameters of the super-hydrophobic silica aerogel obtained in this example, such as specific surface area, hydrophobic angle, pore volume and density, can be seen in Table 1.

[0096] Example 7

[0097] (1) The industrial waste chlorosilane azeotrope is added dropwise into a mixture of n-heptane and water at 10 °C to obtain silica sol. The molar percentage of trimethylchlorosilane in the chlorosilane azeotrope is 45%, and the molar percentage of silicon tetrachloride is 55%. The molar ratio of chlorosilane azeotrope, n-heptane and water is 1:5:2, and the dropwise rate is 10 L / min.

[0098] (2) The silica sol obtained in step 1) is heated to obtain silica wet gel through polycondensation reaction. The heating time is 24 h and the temperature is 60 °C.

[0099] (3) The silica wet gel obtained in step 2) is dried with supercritical CO2 after being replaced with ethanol solvent for 3 times. The drying time is 48 h to obtain super-hydrophobic silica aerogel.

[0100] The physical parameters of the superhydrophobic silica aerogel obtained in this example, such as specific surface area, hydrophobic angle, pore volume and density, are shown in Table 1.

[0101] Example 8

[0102] (1) The industrial waste chlorosilane azeotrope was added dropwise into a mixture of dimethyl sulfoxide and water at 20°C to obtain a silica sol. The molar percentage of trimethylchlorosilane in the chlorosilane azeotrope was 25%, and the molar percentage of silicon tetrachloride was 75%. The molar ratio of chlorosilane azeotrope, dimethyl sulfoxide and water was 1:4:5, and the dropwise rate was 0.01 L / min.

[0103] (2) The silica sol obtained in step 1) was heated to obtain a silica wet gel through polycondensation reaction. The heating time was 24 h, and the temperature was 60°C.

[0104] (3) The silica wet gel obtained in step 2) was replaced with water and dimethyl sulfoxide solvent for 6 times and then dried with supercritical CO2 for 6 h to obtain a superhydrophobic silica aerogel.

[0105] The physical parameters of the superhydrophobic silica aerogel obtained in this example, such as specific surface area, hydrophobic angle, pore volume and density, are shown in Table 1.

[0106] Table 1. Structure and performance parameters of the superhydrophobic silica aerogel obtained in Examples 1-8

[0107] Example Hydrophobic angle Specific surface area (m 2 / g) Pore volume (cm 3 / g) Density (mg / cm 3 )]]> 1 151.7° 741 0.6 171 2 152.3° 853 4 59 3 156.8° 977 1.3 45 4 150.1° 546 1.1 82 5 155.0° 531 3.3 30 6 158.2° 100 0.5 300 7 150.0° 758 3.7 125 8 160.0° 1200 2.5 172

[0108] Comparative Example 1

[0109] (1) Methanol was slowly added to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride under water bath constant temperature (5°C) to generate organosilicon monomers and hydrogen chloride, then water was added, and hydrogen chloride was removed by reflux (temperature 130°C, time 1 h), and cooled to room temperature to obtain a silica aerogel precursor. The dropwise rate of methanol was 50 mL / min. The molar ratio of water, methanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, silicon tetrachloride was 1:5:0.1:0.2:0.3:0.4.

[0110] (2) Water and ammonia were added to the silica aerogel precursor solution obtained in step 1) to obtain a silica gel through polycondensation reaction; the molar ratio of water:ammonia:chlorosilane monomer was 1.5:10 -4 :1, the polycondensation reaction time was 48 h, and the temperature was 60°C.

[0111] (3) The silica gel obtained in step 2) was replaced with ethanol solvent for 6 times and then dried with supercritical ethanol for 48 h to obtain a superhydrophobic silica aerogel.

[0112] Comparative Example 1 uses several pure chlorosilanes mixed together as the silicon source, which is expensive. The chlorosilanes must first be added to an alcohol organic reagent, and the chemical reaction principle is that the chlorosilane and the alcohol organic reagent first generate a silicon ester, and then further hydrolysis. In the present application, the industrial waste chlorosilane azeotrope does not add an alcohol organic reagent, and the hydrolysis process does not pass through the silicon esterification process of the alcohol organic solvent, and directly generates silicon hydroxyl. The sol mechanism is different.

[0113] Furthermore, the gel process in Comparative Example 1 requires the addition of an alkali catalyst, while the silica sol of the present application uses the hydrochloric acid generated by the chlorosilane azeotrope for acid catalysis one-step gelation, and the polycondensation reaction conditions and chemical reaction principle are different.

[0114] Comparative Example 2

[0115] (1) Under the condition of water bath constant temperature (30℃), methanol was slowly added to trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane and silicon tetrachloride to generate organosilicon monomers and hydrogen chloride, then water was added, and hydrogen chloride was removed by reflux (temperature 60℃, time 12h), and cooled to room temperature to obtain a silica aerogel precursor. Among them, the drop rate of methanol is 2000mL / min. The molar ratio of water, methanol, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, silicon tetrachloride is 3:10:0:0:0.5:0.5.

[0116] (2) Water and sodium carbonate were added to the silica aerogel precursor solution obtained in step 1) to obtain a silica gel by polycondensation reaction; wherein the molar ratio of water: sodium carbonate: chlorosilane monomer is 1:10 -1 :1, the polycondensation reaction time is 48h, and the temperature is 60℃.

[0117] (3) The silica gel obtained in step 2) was replaced with ethanol solvent for 6 times and then supercritical carbon dioxide was dried, and the drying time was 12 hours to obtain a superhydrophobic silica aerogel.

[0118] Compared with Example 3, the methanol used in this comparative example contains hydroxyl groups, which can react with methyltrichlorosilane or silicon tetrachloride to form a silicon ester, and then hydrolyze the silicon ester with water. The butanone in Example 3 only acts as a solvent and does not participate in the reaction, and the chemical reaction is a chlorine substitution reaction, and the chemical reaction mechanism is different. And using butanone as the reaction solvent can inhibit phase separation, and the specific surface area of the superhydrophobic silica aerogel obtained in Example 3 is 977m 2 / g, which is larger than 196m 2 / g of this comparative example.

[0119] Comparative Example 3

[0120] To 641 g (35.6 moles) of water cooled to 70 °C, 135 g (0.8 moles, 91.2 mL) of silicon tetrachloride (SiCl4) (cooled to 7 °C) was added slowly drop-wise. The calculated silica concentration of the wet gel formed in this process and associated with the exotherm was 6.1% by weight.

[0121] The gels in experiments 1, 2, and 3 were aged for 30 minutes at 50 °C, while the gel in experiment 4 was aged for 2 hours.

[0122] For silylation, 100 g of the hydrogel was suspended in 100 mL of hexamethyldisiloxane (HMDSO) and then 52.5 g (0.5 moles, 70 mL) of trimethylchlorosilane was added. Within a few minutes, the aqueous phase formed below the HMDSO phase. After 30 minutes, the HMDSO phase was removed from the hydrophobic HMDSO wet gel, which was then dried. Drying was performed under a stream of hot nitrogen (1500 L / hour, 200 °C) for 1 hour.

[0123] Comparative Example 3 used reagent grade silicon tetrachloride as the silicon source, while the industrial waste chlorosilane azeotrope used in the present invention is primarily composed of silicon tetrachloride and trimethylchlorosilane. In the sol-gel process, not only the hydrolysis and polycondensation of silicon tetrachloride, but also the hydrolysis and polycondensation of trimethylchlorosilane must be considered.

[0124] The silica wet gel in Comparative Example 3 must be subjected to additional silylation surface hydrophobic modification to obtain the superhydrophobic silica aerogel, and the surface hydrophobic modification in Comparative Example 3 is performed after the gel, and the chemical reaction principle is to graft silane groups on the surface of silica nanoparticles. While the trimethylchlorosilane in the silicon source industrial waste chlorosilane azeotrope in the present invention not only acts as a silicon source, but also acts as a surface hydrophobic modifier, so that the sol-gel and surface modification are completed simultaneously, and the chemical reaction mechanism is that the silicon tetrachloride and trimethylchlorosilane form oligomers with methyl groups under the action of water, and the oligomers form superhydrophobicity after gelation with the methyl groups, and additional silylation is not required.

[0125] In addition, the present inventors also prepared a series of superhydrophobic silica aerogels using other raw materials and process conditions listed in the specification, and in the manner of Examples 1-8. It was found through testing that these superhydrophobic silica aerogels also had the various excellent properties described in the specification.

[0126] It should be understood that the above description is only some embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the art, other modifications and improvements can be made without departing from the inventive concept of the present application, and these all belong to the protection scope of the present application.

Claims

1. A method for preparing superhydrophobic silica aerogel using industrial waste chlorosilane azeotropes, characterized in that, include: An industrial waste chlorosilane azeotrope is provided, wherein the main components of the industrial waste chlorosilane azeotrope include trimethylchlorosilane and silicon tetrachloride, wherein the molar percentage of trimethylchlorosilane is 20-50% and the molar percentage of silicon tetrachloride is 50-80%. At a first temperature, the industrial waste chlorosilane azeotrope is added dropwise to a mixture of water and a non-alcoholic organic solvent to react and obtain a silica sol. The molar ratio of the non-alcoholic organic solvent to the industrial waste chlorosilane azeotrope is 0.1 to 5:

1. The first temperature is 5 to 25°C. The non-alcoholic organic solvent is selected from any one or a combination of two or more of tetrahydrofuran, butanone, acetonitrile, dimethyl sulfoxide, n-hexane, and n-heptane. The molar ratio of water to the industrial waste chlorosilane azeotrope is 1 to 5:

1. The silica sol is heated to a second temperature, and a silica wet gel is obtained through a polycondensation reaction; the second temperature is 25~80℃, and the heating time is 1~48h. Solvent replacement was performed on the wet silica gel to obtain silica gel, which was then dried to obtain superhydrophobic silica aerogel.

2. The method according to claim 1, characterized in that: The industrial waste chlorosilane azeotrope originates from byproducts of industrial organosilicon monomer production or industrial monocrystalline silicon production.

3. The method according to claim 1, characterized in that: The first temperature is 10~20℃.

4. The method according to claim 1, characterized in that: The dropping rate of the industrial waste chlorosilane azeotrope is 0.001~10 L / min.

5. The method according to claim 4, characterized in that: The dropping rate of the industrial waste chlorosilane azeotrope is 0.01~0.1 L / min.

6. The method according to claim 1, characterized in that: The molar ratio of the non-alcoholic organic solvent to the industrial waste chlorosilane azeotrope is 1~4:

1.

7. The method according to claim 1, characterized in that: The molar ratio of water to industrial waste chlorosilane azeotrope is 2~4:

1.

8. The method according to claim 1, characterized in that: The second temperature is 40~60℃.

9. The method according to claim 1, characterized in that: The heating time is 6 to 24 hours.

10. The method according to claim 1, characterized in that: The solvent used for solvent replacement is selected from any one or a combination of two or more of water, tert-butanol, ethanol, acetone, n-hexane, tetrahydrofuran, and dimethyl sulfoxide.

11. The method according to claim 1, characterized in that: The solvent replacement is performed 1 to 10 times.

12. The method according to claim 11, characterized in that: The solvent replacement is performed 3 to 6 times.

13. The method according to claim 10, characterized in that: The drying process is selected from any one or a combination of two or more of atmospheric pressure drying, vacuum drying, and supercritical drying.

14. The method according to claim 13, characterized in that: The temperature for atmospheric pressure drying is 20~200℃, and the drying time is 1~24h.

15. The method according to claim 14, characterized in that: The temperature for atmospheric pressure drying is 60~100℃.

16. The method according to claim 13, characterized in that: The vacuum drying is freeze-vacuum drying and / or ambient temperature vacuum drying, wherein the cold trap temperature for freeze-vacuum drying is -45 to -80°C. o C, drying time is 6~48h.

17. The method according to claim 13, characterized in that: The supercritical fluid used in the supercritical drying is selected from either supercritical CO2 or supercritical ethanol, and the drying time is 6 to 48 hours.

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