CN117303379A - Super-hydrophobic modification method of silica gel and super-hydrophobic silica aerogel powder - Google Patents

Abstract

The invention relates to the technical field of aerogel material production, in particular to a super-hydrophobic modification method of silica gel and super-hydrophobic silica aerogel powder. The method comprises the following steps: step 1, crushing silica gel into micron-sized small gel particles; step 2, slowly dripping the chlorosilane azeotrope into absolute ethyl alcohol at the temperature of less than 10 ℃ to react to obtain a mixed solution; step 3, adding the mixed solution obtained in the step 2 into the small gel particles obtained in the step 1 for reaction to obtain hydrophobically modified silica gel; and step 4, washing and drying to obtain the super-hydrophobic silica aerogel powder. The method is simple and easy to operate, the resource utilization of the chlorosilane azeotrope is realized, and the prepared silicon oxide aerogel has superhydrophobicity.

Description

A superhydrophobic modification method of silica gel and superhydrophobic silica aerogel Powder

Technical field

The invention relates to the technical field of airgel material production, and in particular to a superhydrophobic modification method of silica gel and superhydrophobic silica airgel powder.

Background technique

Silica (SiO ₂ ) airgel material has a nanoporous skeleton structure and high porosity. It is a solid material with pores filled with gaseous dispersion medium. The large specific surface area, low thermal conductivity and low density endow the silica airgel material with various properties, such as chemical inertness, thermal insulation, sound insulation and noise reduction, shock absorption and energy absorption, selective adsorption and other properties. It has excellent mechanical and optical properties. , acoustics, electrical and electronics, thermal, aerospace, construction and adsorption separation and other fields have broad application potential. However, because the surface of the silica material contains a large number of hydroxyl groups, the silica aerogel is usually hydrophilic. After being exposed to the air for a long time, its nanopores will absorb moisture in the air due to capillary action. As a result, the airgel skeleton structure collapses, a large number of closed pores and microporous structures appear, and the specific surface area of the airgel is seriously reduced, which in turn leads to the deterioration or even disappearance of the adsorption, heat insulation, and heat preservation properties of the silica airgel material.

In order to maintain a good skeleton structure of silica, it is usually hydrophobically modified using some hydrophobic modifiers. For example, US patent application US20180002181A1 discloses a method for preparing hydrophobic silica aerogels. First, a water glass dispersion is prepared, and then a mixture of a hydrophobic modifier and a non-polar organic solvent is used to hydrophobically modify the silica. , to obtain hydrophobic silica sol, and then through gelation, drying and other processes to obtain hydrophobic silica aerogel. The obtained hydrophobic silica aerogel has a high specific surface area, and due to the hydrophobic modification, It can better maintain its hole structure. Another example is the Chinese patent application CN114477194A, which discloses the preparation of hydrophobic silica aerogels based on chemical vapor deposition. First, bulk or powdered silica aerogels are prepared, and then the bulk or powdered silica aerogels are prepared based on the vapor deposition method. Silica aerogel is hydrophobically modified to obtain hydrophobic silica aerogel. The hydrophobic angle of this aerogel powder is about 151°, which can better prevent the collapse of the prepared silica water-absorbing structure. Another example is Chinese patent CN113213492B, which discloses superhydrophobic silica aerogels and their preparation methods, superhydrophobic porous membranes and their preparation methods and applications. The dehydration condensation reaction occurs by mixing alkaline silica sol and organic alkoxysilane. An alkyl-grafted silica hydrogel is generated to achieve the purpose of hydrophobic modification of the gel.

The above modification methods have the following problems: they need to add a large amount of non-polar organic solvents, which is not conducive to environmental protection; or the modification process of this method is complicated and requires high equipment, and the modification effect is not excellent enough; or the high purity used Organic modifiers are expensive and not suitable for industrial production. In view of this, the object of the present invention is to provide a low-cost and simple process for superhydrophobic modification of silica gel suitable for industrial production and to provide superhydrophobic silica aerogel powder prepared by the method.

Contents of the invention

In order to solve the above problems, the present invention provides a low-cost and simple process for superhydrophobic modification of silica gel suitable for industrial production and a superhydrophobic silica aerogel powder prepared by the method. The specific technical solutions are as follows:

A first aspect of the invention provides a method for superhydrophobic modification of silica gel, which includes the following steps:

Step 1. Take the silica alcohol gel and break it into micron-sized small gel particles;

Step 2: Slowly add the chlorosilane azeotrope dropwise into absolute ethanol of less than 10°C to react to obtain a mixed solution;

Step 3: Add the mixed solution obtained in Step 2 to the small gel particles described in Step 1 for reaction to obtain hydrophobically modified silica gel;

Step 4: Wash and dry to obtain superhydrophobic silica airgel powder.

Specifically, the silica alcohol gel described in step 1 is a silica gel in which the gel skeleton is filled with alcohol; specifically, the preparation process of the silica alcohol gel described in step 1 is: take the The silicone gel is soaked in an alcohol solvent for more than 48 hours. The alcohol solvent includes methanol, ethanol, or ethylene glycol, and is anhydrous alcohol.

In some embodiments, the micron-sized small gel particles are particles with a particle size of 10-40 μm. On the one hand, particle sizes in this range react more fully during the process of strengthening the skeleton and modifying them. On the other hand, the particles If the diameter is too small, such as less than 10 μm, its structure will be easily destroyed in an acidic environment.

Specifically, the purpose of using absolute ethanol less than 10°C in step 2 is to control the alcoholysis rate of the chlorosilane azeotrope and prevent the alcoholysis of the chlorosilane azeotrope from violently generating white precipitates or flocs, which will affect the prepared gas. Gel properties.

Specifically, the mass ratio of the chlorosilane azeotrope and absolute ethanol in step 2 is 1:0.8~1.6.

Specifically, the mass ratio of the chlorosilane azeotrope in step 2 to the silica gel in step 1 is 1~1.5:0.8~1.

Specifically, the content of trimethylchlorosilane in the chlorosilane azeotrope described in step 2 is 45~60wt%, and the content of silicon tetrachloride is 30~50wt%. In this application, the chlorosilane azeotrope plays the role of secondary silicon source enhancement, mainly silicon tetrachloride and part of trimethylchlorosilane. It can be alcoholyzed in absolute ethanol less than 10°C to produce different functionalities. Ethoxysilane and trimethylsilanol (trimethylchlorosilane reacts very slowly), ethoxysiloxane and trimethylsilanol can respectively condense with the silicone hydroxyl groups on the gel surface to act as secondary silicone The source enhances the strength of the silica gel skeleton, making it less likely to collapse; most other trimethylchlorosilanes play a modifying role in the chlorosilane azeotrope, which can modify the gel surface and make the oxidation Silicone gel is hydrophobic and does not absorb water easily.

Specifically, the reaction time described in step 2 is 1 to 2 hours.

Specifically, the reaction described in step 3 is to perform the reaction below 10°C for 0.5-1h under high-speed stirring conditions, and then raise the temperature to 60~80°C for 2~3h; the high-speed stirring speed is 400~600rpm.

Specifically, the washing described in step 4 is washing with pure water.

Specifically, the drying described in step 4 is normal pressure drying or supercritical drying; the normal pressure drying medium is a low surface tension organic solvent, and the low surface tension organic solvent is n-hexane, methanol, ethanol, or isopropyl alcohol. and dimethyl ether; the supercritical drying medium is carbon dioxide.

A second aspect of the present invention provides a superhydrophobic silica airgel powder prepared by any of the above methods.

The invention uses the industrial by-product chlorosilane azeotrope as a hydrophobic modifier. Silicon tetrachloride and part of the trimethylchlorosilane in the chlorosilane azeotrope are first ethanolized at a slow rate in anhydrous ethanol of less than 10°C. The decomposition produces ethoxysilane and trimethylsilanol with different functionalities (the reaction of trimethylsilyl chloride is very slow). Ethoxysiloxane and trimethylsilanol can be condensed with the silicone hydroxyl groups on the gel surface respectively. It acts as a secondary silicon source to enhance the strength of the silica gel skeleton, making it less likely to collapse; at the same time, trimethylchlorosilane can modify the gel surface, making the silica gel hydrophobic and less likely to absorb water. The beneficial effects brought by the technical solution of the present invention are as follows:

(1) The present invention uses the industrial by-product chlorosilane azeotrope, which is cheap, easy to obtain, and difficult to process, as a hydrophobic modifier to hydrophobically modify the silica gel, greatly reducing the hydrophobicity of the hydrophobic silica aerogel. The production cost is reduced, and the resource utilization of chlorosilane azeotrope can be realized, which improves the economic value of chlorosilane azeotrope;

(2) Silicon tetrachloride and trimethylchlorosilane in the chlorosilane azeotrope can enhance the gel network structure and improve the hydrophobicity of the gel after alcoholysis, thereby improving the aerogel pore size uniformity and structure. The stability is improved, and the finally prepared silica aerogel has better thermal insulation properties and better hydrophobic properties;

(3) The method provided by the present invention is simple and easy to operate, and is suitable for large-scale industrial production.

Detailed ways

The technical solution of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

Example 1

Step 1. Take 200g of silica alcohol gel and break it into micron-sized small gel particles;

Step 2. 278g of chlorosilane azeotrope (mainly including 40wt% of trimethylchlorosilane and 55wt% of silicon tetrachloride) was slowly and uniformly added dropwise to 334g of absolute ethanol at 0°C for 1.5h. During the reaction Continuously remove the hydrogen chloride gas generated in the system to obtain a mixed liquid;

Step 3. Add the mixture obtained in step 2 to the small gel particles obtained in step 1 at one time, stir and react at 10°C for 1 hour at 500 rpm, then raise the temperature to 70°C, and continue stirring for 2.5 hours. During the reaction Continuously remove the generated hydrogen chloride gas to obtain hydrophobically modified silica gel;

Step 4: Wash the hydrophobically modified silica gel obtained in step 3 twice with an equal volume of pure water, and then dry to obtain superhydrophobic silica airgel powder.

Example 2

Step 1. Take 200g of silica hydrogel, soak the gel with an equal volume of ethanol for 48 hours, and then break it into micron-sized small gel particles;

Step 2. Add 278g of chlorosilane azeotrope (mainly including 40wt% trimethylchlorosilane and 55wt% silicon tetrachloride) dropwise into 222.4g of absolute ethanol at 0°C and react for 1.5h. During the reaction process, the hydrogen chloride gas generated in the system is continuously removed to obtain a mixed liquid;

Step 3. Add the mixture obtained in Step 2 to the small gel particles obtained in Step 1 at one time, stir the reaction at 10°C for 1 hour at 500 rpm, and continue stirring for 2.5 hours. During the reaction, the hydrogen chloride gas generated is continuously removed. , to obtain hydrophobically modified silica gel;

Step 4: Wash the hydrophobically modified silica gel obtained in step 3 twice with an equal volume of pure water, and then dry to obtain superhydrophobic silica airgel powder.

Example 3

Step 1. Take 200g of silica hydrogel, soak the gel with an equal volume of ethanol for 48 hours, and then break it into micron-sized small gel particles;

Step 2. 278g of chlorosilane azeotrope (mainly including 40wt% of trimethylchlorosilane and 55wt% of silicon tetrachloride) was slowly and uniformly added dropwise to 444.8g of 0°C absolute ethanol for 1.5h. The reaction process Continuously remove the hydrogen chloride gas generated in the system to obtain a mixed liquid;

Step 3. Add the mixture obtained in step 2 to the small gel particles obtained in step 1 at one time, stir and react at 10°C for 1 hour at 500 rpm, then raise the temperature to 70°C, and continue stirring for 2.5 hours. During the reaction Continuously remove the generated hydrogen chloride gas to obtain hydrophobically modified silica gel;

Step 4: Wash the hydrophobically modified silica gel obtained in step 3 twice with an equal volume of pure water, and then dry to obtain superhydrophobic silica airgel powder.

Example 4

Step 1. Take 148.3g of silica hydrogel, soak the gel with an equal volume of ethanol for 48 hours, and then break it into micron-sized small gel particles;

Step 2. 278g of chlorosilane azeotrope (mainly including 40wt% of trimethylchlorosilane and 55wt% of silicon tetrachloride) was slowly and uniformly added dropwise to 222.4g of 0°C absolute ethanol for 1.5h. The reaction process Continuously remove the hydrogen chloride gas generated in the system to obtain a mixed liquid;

Step 3. Add the mixture obtained in step 2 to the small gel particles obtained in step 1 at one time, stir and react at 10°C for 1 hour at 500 rpm, then raise the temperature to 70°C, and continue stirring for 2.5 hours. During the reaction Continuously remove the generated hydrogen chloride gas to obtain hydrophobically modified silica gel;

Step 4: Wash the hydrophobically modified silica gel obtained in step 3 twice with an equal volume of pure water, and then dry to obtain superhydrophobic silica airgel powder.

Example 5

Step 1. Take 278g of silica hydrogel, soak the gel with an equal volume of ethanol for 48 hours, and then break it into micron-sized small gel particles;

Step 2. 278g of chlorosilane azeotrope (mainly including 40wt% of trimethylchlorosilane and 55wt% of silicon tetrachloride) was slowly and uniformly added dropwise to 334g of absolute ethanol at 0°C for 1.5h. During the reaction Continuously remove the hydrogen chloride gas generated in the system to obtain a mixed liquid;

Step 3. Add the mixture obtained in step 2 to the small gel particles obtained in step 1 at one time, stir and react at 10°C for 1 hour at 500 rpm, then raise the temperature to 70°C, and continue stirring for 2.5 hours. During the reaction Continuously remove the generated hydrogen chloride gas to obtain hydrophobically modified silica gel;

Step 4: Wash the hydrophobically modified silica gel obtained in step 3 twice with an equal volume of pure water, and then dry to obtain superhydrophobic silica airgel powder.

Example 6

Step 1. Take 200g of silica hydrogel, soak the gel with an equal volume of ethanol for 48 hours, and then break it into micron-sized small gel particles;

Step 2. 278g of chlorosilane azeotrope (mainly including 40wt% of trimethylchlorosilane and 55wt% of silicon tetrachloride) was slowly and uniformly added dropwise to 334g of 10°C absolute ethanol for 1.5h. During the reaction Continuously remove the hydrogen chloride gas generated in the system to obtain a mixed liquid;

Step 3. Add the mixture obtained in step 2 to the small gel particles obtained in step 1 at one time, stir and react at 10°C for 1 hour at 500 rpm, then raise the temperature to 70°C, and continue stirring for 2.5 hours. During the reaction Continuously remove the generated hydrogen chloride gas to obtain hydrophobically modified silica gel;

Step 4: Wash the hydrophobically modified silica gel obtained in step 3 twice with an equal volume of pure water, and then dry to obtain superhydrophobic silica airgel powder.

Comparative example 1

In this embodiment, the mass ratio of the chlorosilane azeotrope to ethanol is 1:1.2; the mass ratio of the chlorosilane azeotrope to silica gel is 1.25:0.9. The specific preparation method is as follows:

Step 1. Take 200g of silica hydrogel, soak the gel with an equal volume of ethanol for 48 hours, and then break it into micron-sized small gel particles;

Step 2. 278g of chlorosilane azeotrope (mainly including 40wt% of trimethylchlorosilane and 55wt% of silicon tetrachloride) was slowly and uniformly added dropwise to 334g of 15°C absolute ethanol for 1.5h. During the reaction Continuously remove the hydrogen chloride gas generated in the system to obtain a mixed liquid;

Step 3. Add the mixture obtained in Step 2 to the small gel particles obtained in Step 1 at one time, stir for 1 hour at 500 rpm, then raise the temperature to 70°C, and continue stirring for 2.5 hours. During the reaction, the hydrogen chloride generated is continuously removed. gas to obtain hydrophobically modified silica gel;

Step 4: Wash the hydrophobically modified silica gel obtained in step 3 twice with an equal volume of pure water, and then dry to obtain superhydrophobic silica airgel powder.

Test Results

The hydrophobic angle, rolling angle and thermal conductivity of the superhydrophobic silica aerogels prepared in the Examples and Comparative Examples after being exposed to the air for 3 days were tested.

Table 1 Performance test of superhydrophobic silica airgel prepared in Examples and Comparative Examples

It can be seen from the above test results that the superhydrophobic silica aerogel prepared by the method of the present invention in the embodiment has an enhanced gel skeleton structure, a relatively stable structure, good superhydrophobic performance, and good thermal insulation performance. . Comparative Example 1: Due to the high temperature of the alcoholysis of methyl chlorosilane and the fast reaction rate, some azeotropes directly generate powdery particles, which cannot hydrophobically modify the silica gel. The prepared silica gas The gel has poor hydrophobic properties.

Claims (9)

1. A method for superhydrophobic modification of silica gel, characterized in that it includes the following steps: Step 1. Take the silica alcohol gel and break it into micron-sized gel particles; Step 2: Slowly add the chlorosilane azeotrope dropwise into absolute ethanol of less than 10°C to react to obtain a mixed solution; Step 3: Add the mixed solution obtained in Step 2 to the small gel particles described in Step 1 for reaction to obtain hydrophobically modified silica gel; Step 4: Wash and dry to obtain superhydrophobic silica airgel powder. 2. The superhydrophobic modification method of silica gel as claimed in claim 1, characterized in that the preparation process of the silica alcohol gel in step 1 is: taking the silica gel in an alcohol solvent Soak for more than 48 hours, and the alcohol includes methanol, ethanol, or ethylene glycol. 3. The superhydrophobic modification method of silica gel as claimed in claim 1, wherein the mass ratio of the chlorosilane azeotrope and absolute ethanol in step 2 is 1:0.8~1.6. 4. The superhydrophobic modification method of silica gel as claimed in claim 1, characterized in that the content of trimethylchlorosilane in the chlorosilane azeotrope described in step 2 is 45~60wt%, and the content of tetrachlorosilane is 45~60wt%. The silicon content is 30~50wt%. 5. The superhydrophobic modification method of silica gel as claimed in claim 1, characterized in that the mass ratio of the chlorosilane azeotrope described in step 2 to the silica gel in step 1 is 1~1.5 :0.8~1. 6. The superhydrophobic modification method of silica gel as claimed in claim 1, characterized in that the reaction described in step 3 is to react at 10° C. and below under high-speed stirring conditions of 400 to 600 rpm, and then heat up. React at 60~80℃. 7. The superhydrophobic modification method of silica gel according to claim 1, wherein the washing in step 4 is washing with pure water. 8. The superhydrophobic modification method of silica gel according to claim 1, wherein the drying in step 4 is normal pressure drying or supercritical drying. 9. A superhydrophobic silica airgel powder obtained by the method of any one of claims 1 to 8.