Preparation method and application of normal-pressure dried super-hydrophobic aerogel powder

Abstract

The invention provides a preparation method and application of normal-pressure dried super-hydrophobic aerogel powder. The preparation method of the normal-pressure dried super-hydrophobic aerogel powder comprises the following steps: S1, mixing silicon dioxide wet gel in a crushed state with a modified solution and a solvent, stirring at 50-80 DEG C for 6-8 hours, eluting with the solvent after the reaction is finished, and carrying out filter pressing to obtain modified wet gel; and S2, drying the modified wet gel obtained in the step S1 under normal pressure to obtain the modified wet gel, in the step S1, a preparation method of the modified liquid comprises the following steps: mixing octamethylcyclotetrasiloxane and a catalyst, continuously introducing saturated water vapor at 60-70 DEG C, and reacting for 1.5-2 hours; the catalyst is an alkaline compound. According to the preparation method provided by the invention, the aerogel powder obtained by normal-pressure drying is low in density and good in hydrophobicity.

Description

Technical Field

[0001] The present invention relates to the technical field of synthesis of silicon dioxide aerogel, and more specifically to a method for preparing super-hydrophobic aerogel powder dried at normal pressure and application thereof. Background Art

[0002] Hydrophobic aerogels are an important research topic in the field of materials science in recent years. Aerogels are ultra-light, porous materials with a three-dimensional network structure. Due to their extremely low density, high porosity and large specific surface area, they exhibit excellent performance in the fields of heat, mechanics, acoustics and optics, and are widely used in thermal insulation materials. However, the traditional supercritical drying method for preparing aerogels has problems such as complex equipment, high energy consumption and high risk, which limits its large-scale promotion and application.

[0003] In this context, the technology of preparing aerogel powder by drying at normal pressure is particularly important. By optimizing the sol-gel preparation process and combining the surface hydrophobic modification, the SiO 2 Normal pressure preparation of aerogel powder. Compared with traditional methods, this technology not only simplifies the process and reduces production costs, but also significantly improves production efficiency, making it possible for the industrial production of hydrophobic aerogel powder, and has broad application prospects and industrial value.

[0004] However, in the prior art, the preparation of hydrophobic aerogel powder by normal pressure drying faces at least one of the following technical challenges: the obtained aerogel powder has a high density and poor hydrophobic properties, thereby affecting the performance of the obtained aerogel. Summary of the invention

[0005] In order to solve or at least partially solve the problems in the prior art, the present invention provides a method for preparing super-hydrophobic aerogel powder by drying at normal pressure. The aerogel powder obtained by the preparation method (using normal pressure drying) has low density and good hydrophobicity.

[0006] The method for preparing super-hydrophobic aerogel powder dried at normal pressure provided by the present invention comprises the following steps:

[0007] S1, mixing the crushed silicon dioxide wet gel with the modifying liquid and the solvent, stirring at 50-80° C. for 6-12 hours, eluting with the solvent after the reaction, and filtering to obtain the modified wet gel;

[0008] S2, drying the modified wet gel obtained in step S1 under normal pressure to obtain;

[0009] In step S1, the preparation method of the modified liquid includes the following steps: mixing octamethylcyclotetrasiloxane and a catalyst, continuously introducing saturated water vapor at 60-70° C., and reacting for 1.5-2 hours; the catalyst is an alkaline compound.

[0010] When the applicant was studying how to reduce the density of the hydrophobic aerogel powder prepared by drying at normal pressure, it was unexpectedly discovered that the modified liquid obtained by the above-mentioned specific preparation method can be used to improve the crushed silica wet gel at a specific temperature (too high temperature will cause the performance of the obtained aerogel powder to deteriorate), which can effectively reduce the density of the aerogel powder prepared by drying at normal pressure.

[0011] In a preferred embodiment of the present invention, in the method for preparing the modified liquid, the catalyst may be potassium hydroxide, sodium hydroxide, lithium hydroxide or concentrated aqueous ammonia, preferably potassium hydroxide.

[0012] In a preferred embodiment of the present invention, in order to further improve the hydrophobicity of the aerogel powder while ensuring low density, in the preparation method of the modified liquid, the mass ratio of octamethylcyclotetrasiloxane to the catalyst is (40-80):1, preferably (60-70):1.

[0013] In a preferred embodiment of the present invention, in order to improve the performance of aerogel powder, the particle size D50 of the crushed silicon dioxide wet gel is 40-60 um.

[0014] In a preferred embodiment of the present invention, in order to improve the performance of aerogel powder, in step S1, the mass ratio of the crushed silicon dioxide wet gel to the modifying liquid is 1:(0.4-2).

[0015] In a preferred embodiment of the present invention, in step S1, the solvent can be one or more of isooctane, n-hexane, acetonitrile, and glycerol, preferably isooctane. The amount of the solvent can be the amount commonly used in the art, for example, 3 to 10 times that of the modified solution.

[0016] In a specific embodiment of the present invention, the silicon dioxide wet gel can be prepared by a method commonly used in the art, and then the silicon dioxide wet gel in a crushed state can be obtained by wet grinding.

[0017] In a preferred embodiment of the present invention, in step S1, the method for preparing the crushed silicon dioxide wet gel comprises the following steps:

[0018] The silicon source, alcohol and the first catalyst are subjected to hydrolysis condensation reaction. After the reaction, the second catalyst is added to carry out polycondensation reaction. After gelation, wet gel is obtained. After aging and ageing steps, isooctane is added for replacement. After removing the isooctane, silicon dioxide wet gel is obtained. After wet grinding, crushed silicon dioxide wet gel is obtained.

[0019] In a preferred embodiment of the present invention, in the method for preparing the wet silica gel, the silicon source may be tetraethoxysilane or polysiloxane.

[0020] In a preferred embodiment of the present invention, in the method for preparing the wet silica gel, the alcohol may be methanol or ethanol.

[0021] In a preferred embodiment of the present invention, in the method for preparing the wet silica gel, the first catalyst is hydrochloric acid, sulfuric acid, phosphoric acid, oxalic acid or hydrofluoric acid, and the amount of the first catalyst added is such that the pH of the system is 2-3.

[0022] In a preferred embodiment of the present invention, in order to reduce the density of the obtained aerogel powder while taking into account the hydrophobic property, in the preparation method of the silicon dioxide wet gel, the mass ratio of the silicon source to the alcohol is 1: (2-10).

[0023] In a specific embodiment of the present invention, the silicon source, alcohol and the first catalyst can be subjected to hydrolysis condensation reaction to obtain a hydrolyzed solution according to the needs, and the hydrolyzed solution is usually stored at low temperature. When needed, the second catalyst is added to the hydrolyzed solution to carry out subsequent reactions.

[0024] In a preferred embodiment of the present invention, in the method for preparing the wet silica gel, the second catalyst is ammonia water, potassium hydroxide, sodium hydroxide, lithium hydroxide or tetramethylammonium hydroxide, and the amount of the second catalyst is such that the pH value of the system is 7 to 8 (preferably 7.2 to 8). In this step, the second catalyst not only plays the role of adjusting the pH value of the system, but also plays a catalytic role. If the amount is too much, the gel time of the silica sol is too short, which affects the performance of the aerogel powder finally obtained.

[0025] In a specific embodiment of the present invention, the gel can be aged and aged using an aging method or aging method commonly used in the art. The present invention does not impose any other special restrictions on the aging and aging methods, and only requires that the gel be fully aged and aged. For example, the gel can be left to stand for aging, or ethanol can be used to age the gel.

[0026] In a preferred embodiment of the present invention, in step S2, the specific step of drying at normal pressure may include: under normal pressure, drying the modified wet gel at 60°C, 80°C, and 110°C in a gradient manner for 2-3h, 2-3h, and 3-4h, respectively.

[0027] In a preferred embodiment of the present invention, all steps of the method for preparing super-hydrophobic aerogel powder by drying at normal pressure provided by the present invention are carried out under normal pressure.

[0028] The atmospheric pressure dried super hydrophobic aerogel powder obtained by the preparation method has low density and good hydrophobicity.

[0029] Another object of the present invention is to provide a super-hydrophobic aerogel powder dried at normal pressure obtained by the above preparation method.

[0030] Another object of the present invention is to provide the above preparation method or the use of the atmospheric pressure dried super hydrophobic aerogel powder obtained by the above preparation method in the preparation of thermal insulation coatings. The thermal insulation coatings can be used in the fields of building insulation fillers and the like.

[0031] The beneficial effects of the present invention are:

[0032] The super-hydrophobic aerogel powder obtained by the preparation method provided by the present invention (including normal pressure drying) has a low density (density not higher than 105kg / m 3 , preferably not more than 100kg / m 3 ), and at the same time is super hydrophobic (i.e., it has excellent hydrophobic properties, with a water contact angle greater than 130°, preferably greater than 145°). At the same time, the preparation method provided by the present invention is simple and economical, and is suitable for industrial production. DETAILED DESCRIPTION

[0033] The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention. In the present invention, if there is no special explanation, "%" means mass percentage.

[0034] Example 1

[0035] This embodiment provides an aerogel powder, comprising the following steps:

[0036] 1) At room temperature and pressure, 152 kg of TMOS tetramethoxysilane and 320 kg of methanol were mixed, and an acidic catalyst of 1 mol / L hydrochloric acid was added to adjust the pH of the system to 2. The mixture was reacted in a reactor for 8 h. After the reaction was completed, the mixture was stored at 7° C. to obtain a hydrolyzate.

[0037] 2) Preparation of modified liquid: 30 kg of octamethylcyclotetrasiloxane and 0.5 kg of potassium hydroxide were added into the reactor, and then the temperature was raised to 60°C, saturated water vapor was continuously introduced, the reaction was carried out for 2 hours, the temperature was lowered and the material was discharged to obtain the modified liquid.

[0038] 3) At room temperature and pressure, the pH value of the hydrolyzate obtained in step 1) is adjusted to 7.5 using 1 mol / L ammonia water, and the mixture is stirred in the reactor for 10 seconds. After the reaction is completed, the wet gel is obtained after the gel is formed, and the gel is run on a conveyor belt for 10 minutes to complete the aging.

[0039] 4) The aged wet gel obtained in step 3) is placed in an aging kettle, ethanol is added to cover the gel and aged for 48 hours. After the aging is completed, the aged wet gel is placed in a stirring kettle, 500 kg of isooctane is added, and the replacement is carried out for 8 hours. The replacement step is repeated twice, and the replacement is completed.

[0040] 5) 450 kg of the wet gel obtained in step 4) after the replacement is wet-ground into powder to a particle size D50 of 50 μm, 100 kg of the modified liquid obtained in step 2) and 400 kg of isooctane are added, and the modification is carried out under stirring at 60° C. for 8 h, and the modification is completed.

[0041] 6) After the modification is completed, the material in the stirred tank in step 5) is repeatedly eluted with isooctane, placed in a filter press, and the excess liquid is discharged to obtain a wet gel.

[0042] 7) The wet gel obtained in step 6) is placed in a drying device and dried at 60° C., 80° C., and 110° C. for 2 h, 2 h, and 4 h, respectively, to obtain aerogel powder.

[0043] Example 2

[0044] The preparation methods provided in this embodiment are the same as those provided in embodiment 1, except that:

[0045] 2) Preparation of modified liquid: 35 kg of octamethylcyclotetrasiloxane and 0.5 kg of sodium hydroxide were added into the reactor, and then the temperature was raised to 70°C, saturated water vapor was continuously introduced, the reaction was carried out for 1.5 hours, the temperature was lowered and the material was discharged to obtain the modified liquid.

[0046] Example 3

[0047] The preparation methods provided in this embodiment are the same as those provided in embodiment 1, except that:

[0048] 2) Preparation of modified liquid: 20 kg of octamethylcyclotetrasiloxane and 0.5 kg of potassium hydroxide were added into the reactor, and then the temperature was raised to 60°C, saturated water vapor was continuously introduced, the reaction was carried out for 2 hours, the temperature was lowered and the material was discharged to obtain the modified liquid.

[0049] Example 4

[0050] The preparation methods provided in this embodiment are the same as those provided in embodiment 1, except that:

[0051] 2) Preparation of modified liquid: 40 kg of octamethylcyclotetrasiloxane and 0.5 kg of potassium hydroxide were added into the reactor, and then the temperature was raised to 60°C, saturated water vapor was continuously introduced, the reaction was carried out for 2 hours, the temperature was lowered and the material was discharged to obtain the modified liquid.

[0052] Example 5

[0053] The preparation methods provided in this embodiment are the same as those provided in embodiment 1, except that:

[0054] 2) Preparation of modified liquid: 15 kg of octamethylcyclotetrasiloxane and 0.5 kg of potassium hydroxide were added into the reactor, and then the temperature was raised to 60°C, saturated water vapor was continuously introduced, the reaction was carried out for 2 hours, the temperature was lowered and the material was discharged to obtain the modified liquid.

[0055] Example 6

[0056] The preparation methods provided in this embodiment are the same as those provided in embodiment 1, except that:

[0057] 2) Preparation of modified liquid: 45 kg of octamethylcyclotetrasiloxane and 0.5 kg of potassium hydroxide were added into the reactor, and then the temperature was raised to 60°C, saturated water vapor was continuously introduced, the reaction was carried out for 2 hours, the temperature was lowered and the material was discharged to obtain the modified liquid.

[0058] Comparative Example 1

[0059] This comparative example provides an aerogel powder, comprising the following steps:

[0060] 1) At room temperature and pressure, 152 kg of TMOS tetramethoxysilane and 320 kg of methanol were mixed, and an acidic catalyst of 1 mol / L hydrochloric acid was added to adjust the pH of the system to 2. The mixture was reacted in a reactor for 8 h. After the reaction was completed, the mixture was stored at 7° C. to obtain a hydrolyzate.

[0061] 2) Modifier: dimethyldiethoxysilane.

[0062] 3) At room temperature and pressure, the pH value of the hydrolyzate obtained in step 1) is adjusted to 7.5 using 1 mol / L ammonia water, and the mixture is stirred in the reactor for 10 seconds. After the reaction is completed, the wet gel is obtained after the gel is formed, and the gel is run on a conveyor belt for 10 minutes to complete the aging.

[0063] 4) The aged wet gel obtained in step 3) is placed in an aging kettle, and ethanol is added to cover the gel for aging. After the aging is completed, the aged wet gel is placed in a stirring kettle, 500 kg of isooctane is added, and the replacement is performed 3 times, each replacement for 8 hours, and the replacement is completed.

[0064] 5) The wet gel obtained after the replacement in step 4) is wet-ground into a pulverized state, 100 kg of the hydrophobic modifier in step 2) and 400 kg of isooctane are added, and the modification is stirred at 60° C. for 8 hours, and the modification is completed.

[0065] 6) After the modification is completed, the material in the stirred tank in step 5) is repeatedly eluted with isooctane, placed in a filter press, and the excess liquid is discharged to obtain a wet gel.

[0066] 7) The wet gel obtained in step 6) is placed in a drying device and dried at 60° C., 80° C., and 110° C. for 2 h, 2 h, and 4 h, respectively, to obtain aerogel powder.

[0067] The properties of the aerogel powders obtained in the examples and comparative examples were measured. The density test method was in accordance with GB / T5211.4, the particle size test method was in accordance with GB / T 19077, and the water contact angle test method was in accordance with GB / T 30693. The results are shown in Table 1.

[0068] Table 1 Performance of aerogel powder

[0069]

[0070] Finally, the method of the present invention is only a preferred embodiment and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing super-hydrophobic aerogel powder dried at normal pressure, characterized in that: The steps include: S1, mixing the crushed silicon dioxide wet gel with the modifying liquid and the solvent, stirring at 50-80° C. for 6-8 hours, eluting with the solvent after the reaction, and filtering to obtain the modified wet gel; S2, drying the modified wet gel obtained in step S1 under normal pressure to obtain; In step S1, the preparation method of the modified liquid includes the following steps: mixing octamethylcyclotetrasiloxane and a catalyst, continuously introducing saturated water vapor at 60-70° C., and reacting for 1.5-2 hours; the catalyst is an alkaline compound.

2. The preparation method according to claim 1, characterized in that: In step S1, the catalyst is potassium hydroxide.

3. The preparation method according to claim 1, characterized in that: In step S1, the mass ratio of octamethylcyclotetrasiloxane to the catalyst is (40-80):

1.

4. The preparation method according to any one of claims 1 to 3, characterized in that In step S1, the mass ratio of the crushed silicon dioxide wet gel to the modifying liquid is 1:(0.4-2).

5. The preparation method according to any one of claims 1 to 3, characterized in that: In step S1, the method for preparing the crushed silicon dioxide wet gel comprises the following steps: The silicon source, alcohol and the first catalyst are subjected to hydrolysis condensation reaction. After the reaction, the second catalyst is added to carry out polycondensation reaction. After gelation, wet gel is obtained. After aging and ageing steps in sequence, isooctane is added for replacement. After removing the solvent, silicon dioxide wet gel is obtained. After wet grinding, crushed silicon dioxide wet gel is obtained.

6. The preparation method according to claim 5, characterized in that: The silicon source is tetraethoxysilane or polysiloxane; and / or, the alcohol is methanol; And / or, the first catalyst is hydrochloric acid, sulfuric acid, phosphoric acid, oxalic acid or hydrofluoric acid.

7. The preparation method according to claim 6, characterized in that: The weight ratio of the silicon source to the alcohol is 1:(2-10).

8. The preparation method according to claim 5, characterized in that: The second catalyst is aqueous ammonia, potassium hydroxide, sodium hydroxide, lithium hydroxide or tetramethylammonium hydroxide, and the amount of the second catalyst used is such that the pH value of the system is 7-8.

9. Super hydrophobic aerogel powder dried at normal pressure obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the preparation method according to any one of claims 1 to 8 or the atmospheric pressure dried super hydrophobic aerogel powder according to claim 9 in the preparation of architectural coatings.

Images