KR101310286B1 - Preparation method of Spherical silica aerogel granules - Google Patents

Abstract

The present invention relates to a method for producing spherical silica airgel granules, and more particularly, a water sol solution is added to an ion exchange resin to obtain a silica sol from which sodium ions have been removed, and this is added to a n-hexane with a surfactant. The present invention relates to a method for preparing spherical silica airgel granules by preparing a -hexane solution, stirring the mixture at a specific rate to form silica sol droplets, and then performing a wet gelation step, a surface modification step, and a drying step. According to the production method of the present invention, it is possible to mass-produce spherical silica airgel granules having a uniform particle size of 100 to 1000 μm in a simple process, and the prepared airgel granules are useful for heat insulating materials, adsorbents, carriers, low dielectric coating films, antireflection films, and the like. Can be applied.

Description

Preparation method of spherical silica airgel granules {Preparation method of Spherical silica aerogel granules}

The present invention relates to a silica airgel granule having a spherical shape and a method for producing the same. Silica airgel is a nanoporous silica (SiO ₂ ) particle forming a three-dimensional network structure and having a porosity of 95% or more.The porosity, specific surface area, and pore volume are very high, and thermal conductivity, dielectric constant, refractive index, etc. Since it is very low, it can be usefully applied to various fields such as heat insulating material, adsorbent, various carriers, low dielectric coating film, antireflection film.

In general, silica airgel can be produced in the form of monolith and powder, and powder can be commercialized in the form of an airgel blanket or airgel sheet by compounding with fibers. Blankets or seats can be bent, folded or cut to any size or shape due to their flexibility, allowing them to be used in jackets or sneakers as well as in industrial applications such as insulation panels for LNG carriers, industrial insulation and space suits, as well as insulation for transportation and vehicles and power generation. It is also applicable to household goods such as household goods. In addition, the use of silica aerogels in fire doors, as well as on the roof and floor in houses such as apartments, has a great effect on fire protection.

Silica airgel powders and granules may be prepared by first preparing silica wet gel and mechanically grinding it, followed by supercritical drying or atmospheric pressure drying. However, in this case, since the process of mechanically grinding the silica wet gel includes a disadvantage that it is very difficult to produce aerogel powder or granule having a certain size.

Korean Unexamined Patent Publication No. 2010-6076 suggests a method for preparing hydrophobized airgel granules without using a separate molding apparatus, agglomeration, compression process, or a solvent or granulation additive under water glass and atmospheric pressure drying conditions. However, the present invention has a disadvantage in that it is difficult to manufacture spherical granules because the size of the granules is not constant because the granules are prepared by first preparing the wet gel and then grinding it at a stirring speed of 50 to 1000 rpm.

Korean Patent Laid-Open Publication No. 2006-133831 maintains the temperature in the range of 200 ~ 600 ℃ in the fluidized bed (fluidized bed), by injecting air vertically upward and horizontal to form a spiral fast air flow inside the fluidized bed bed A process for the production of high purity ultralight silica airgel powder under atmospheric pressure using a continuous process in a fluidized bed bed has been presented. However, the granular silica airgel powder produced by the conventional method exemplified above has a shape in the form of powders, each of which is unevenly called granules, and has a limitation in reducing the particle size.

Another method is to prepare a silica airgel bead by making a droplet from a silica sol, and then dropping the droplet into a solution containing a gelling agent to instantly gel it in a solution and to dry it.

Korean Patent Publication No. 2009-30131 discloses a silica wet gel-forming solution having a pH of 4 to 6 to prepare a granular airgel having a uniform size and shape in a solution state immediately before the wet gel is formed. A method for producing a granular airgel is disclosed by dropping droplets in an oil solution at 0 ° C. and aging in the oil solution to form a wet gel having a more uniform granular form. In this case, there is an advantage that it is possible to manufacture a bead-shaped airgel of a relatively uniform size, but it is disadvantageous that the size of the beads finally obtained is too large because it is not suitable for mass production and it is difficult to manufacture fine droplets.

Accordingly, the present inventors endeavored to develop a method for producing silica airgel granules, and after adding a silica sol and a surfactant to n-hexane, and stirring at a constant rate to obtain a silica sol droplets, wet gelation After completing the surface modification and drying process, it was found that spherical silica airgel granules having a uniform particle size were obtained. Therefore, an object of the present invention is to provide a novel method for producing airgel granules.

The present invention

Adding a water glass solution to an ion exchange resin to obtain silica sol from which sodium ions have been removed;

preparing an n-hexane / silica sol mixed solution by adding the silica sol and a surfactant to n-hexane;

Stirring the n-hexane solution at 400 to 800 rpm to form silica sol droplets;

Wet gelling the silica sol droplets by adding ammonia to the n-hexane solution;

Adding the wet gel to an n-hexane solution containing a silicide to hydrophobize the wet gel surface; And

Drying the hydrophobized wet gel;

It characterized by a spherical silica airgel granules manufacturing method comprising a.

According to the production method of the present invention, a spherical silica airgel granule having a uniform particle size of 100 to 1000 µm can be obtained by a simple process. Therefore, the method for producing airgel granules proposed in the present invention is suitable for mass production, and the prepared airgel granules can be usefully applied to heat insulating materials, adsorbents, carriers, low dielectric coating films, antireflection films, and the like.

1 is an optical micrograph of the spherical silica airgel granules prepared in Examples 1 to 6. (Example 1 (a), Example 2 (b), Example 3 (c), Example 4 (d), Example 5 (e), Example 6 (f)
FIG. 2 is a field emission scanning microscope (FESEM) photograph of spherical silica airgel granules prepared in Examples 1 to 6. (Example 1 (a), Example 2 (b), Example 3 (c), and Example 4 (d), Example 5 (e) and Example 6 (f))
Figure 3 is the result of the FT-IR spectra analysis of the spherical silica airgel granules prepared in Examples 2 to 4. (Example 2 (b), Example 3 (c), Example 4 (d)).

Hereinafter, the present invention will be described in more detail.

According to the present invention, a silica sol and a surfactant are added to n-hexane to prepare a spherical silica sol droplet through stirring, and a gelling accelerator such as ammonia is added to the solution to prepare a spherical wet gel. It relates to a method for producing a spherical granular silica airgel through a solvent replacement and surface modification process for the gel.

First, a water glass solution is added to an ion exchange resin to obtain a silica sol from which sodium ions have been removed. The water glass solution is passed through an ion exchange column containing a strongly acidic ion exchange resin to replace sodium ions in the water glass solution with hydrogen ions of the sulfonic acid group (SO ₃ H) of the ion exchange resin to form a silica sol (silicic acid) of Si-OH. Will generate At this time, as the permeation rate of the water glass solution increases, the SiO ₂ concentration of the silica sol increases in proportion. This is because the longer the time for contact with the resin due to the slower permeation rate, the more SiO ₂ in the water glass during the ion exchange process is adsorbed and gelated on the resin surface and remains in the column. It is preferable that the pHs of the obtained silica sol are 2-3.

Next, the silica sol and a surfactant are added to n-hexane to prepare an n-hexane / silica sol mixed solution. As the surfactant, one or more selected from sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate, and sorbitan monolaurate can be used. It is preferable to use a solitane monooleate (span 80). Such surfactants serve to stabilize silica sol droplets in n-hexane. That is, aggregation of droplets can be prevented by adding surfactant. At this time, the volume ratio of the silica sol and the surfactant is preferably 1: 0.1 to 0.5. If the amount of the surfactant is too small, it is difficult to form droplets of uniform size, and as the amount is increased, the silica sol liquid of the small and uniform size is increased. Select the above range because you can get an enemy but there may be a problem of aggregation between droplets when added in excess.

Next, the n-hexane solution is stirred at 400 to 800 rpm to form silica sol droplets. As the stirring speed increases, a small and uniform size of silica sol droplets can be obtained, and thus the size of the silica airgel can be controlled. However, even if the stirring speed is higher than 800 rpm, the effect of the increase is not large. It is desirable to maintain.

Next, the step of wet gelling the silica sol droplets by adding ammonia to the n-hexane solution. Ammonia is added dropwise to the n-hexane solution in the form of an aqueous solution by using a pipette or the like, and the pH of the n-hexane solution is increased by adding ammonia. At this time, it is preferable to adjust the pH to 5 to 7, and the gelation time is increased in the outside of this range may cause a problem that it is difficult to produce spherical granules due to aggregation between silica sol droplets. More preferably, the pH may be adjusted to 6 to 6.5. If the above range is satisfied, the gelation is completed within 10 minutes, and a silica wet gel in the form of droplets can be obtained.

Next, the wet gel is added to an n-hexane solution containing a silylating agent to hydrophobize the wet gel surface. The silylating agent is selected from hexamethyldisilane, ethyltriethoxysilane, trimethoxysilane, triethylethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, trimethylchlorosilane and triethylchlorosilane. More than one species may be used, but is not limited thereto. The volume ratio of the n-nucleic acid solution containing the silylating agent to the wet gel is preferably 1: 1 to 4, and when the volume ratio exceeds 1: 4, the surface modification rate is sharply maintained to maintain the shape of the silica wet gel. If the volume ratio is less than 1: 1, the surface modification rate may be slow and the density of granules may increase. In addition, the concentration of the silylating agent in the n-hexane solution is preferably 5 to 10% by volume. If the volume is less than 5% by volume, the granules may be densified during drying, which may result in a small pore size and inability to prepare porous silica granules. Can be. This surface modification process is carried out at room temperature for about 9 hours, it is good to repeat about 4 to 6 times.

The hydrophobized wet gel can then be dried to obtain spherical silica airgel granules. A drying method is not specifically limited, For example, it can dry under normal pressure using an oven.

According to the silica airgel manufacturing method of the present invention, by controlling the content of the surfactant and the stirring speed of the n-hexane solution, the particle size is about 100 ~ 1000 ㎛, the specific surface area is 650 ~ 750 m ² / g, uniform uniform size Silica airgel granules can be obtained, and the silica airgel manufacturing method is simple and the production process is excellent in productivity. The manufactured silica airgel granules can be usefully applied to the airgel granules, heat insulating material, adsorbent, carrier, low dielectric coating film, antireflection film and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited by the following Examples.

[ Example ]

Example 1

After diluting water glass (sodium silicate, Youngil Chemical, silica content of 28-30 wt%, SiO ₂ : Na ₂ O = 3.52: 1) and distilled water to prepare a water glass solution having 8 wt% of SiO ₂ , it was strongly acidic ion Silica sol was prepared by removing sodium ions in a water glass solution by passing through an exchange resin (Amberlite, IR 120H, H. Rohm & Hass co.) At a rate of 30 mL / min. The SiO ₂ content in the silica sol was about 5.4 wt% and the pH was about 2.2. 10 mL of the prepared silica sol and 1 mL of the surfactant were put in a glass container using a micro pipette, and 40 mL of n-hexane was added to prepare an n-hexane solution. A magnetic bar was added to the n-hexane solution and stirred at 600 rpm for about 1 hour to form silica sol droplets. During stirring, 0.26 mL of 1 M NH ₄ OH solution was added dropwise with a micropipette to adjust the pH to about 6 and wet the gel for about 10 minutes. Thereafter, a wet gel was added to an n-hexane solution containing 10% by volume of trimethylchlorosilane (ACROS Co., Ltd.), and the solution was replaced six times every nine hours. The wet gel with hydrophobically modified surface was dried under normal pressure in an oven at 80 ° C. for 24 hours to obtain spherical silica airgel granules.

Examples 2 to 4

Spherical silica airgel granules were prepared in the same manner as in Example 1 except that the amount of the surfactant was changed to 2 mL (Example 2), 3 mL (Example 3), and 5 mL (Example 4). The amount of the specific surfactant is shown in Table 1.

Examples 5-6

Spherical silica airgel granules were prepared in the same manner as in Example 2 except that the stirring speed of the n-hexane solution was changed to 400 rpm (Example 5) and 800 rpm (Example 6).

Property evaluation

The tap density, porosity, pore volume, average pore diameter and BET surface area of the spherical silica airgel granules prepared in Examples 1 to 6 were measured, and the results are shown in Table 1 below. Tap density and porosity were analyzed with a tap density meter (TAP-2S, Logan Instruments Co.) and pore volume and average pore diameter were calculated by Barrett-Johner-Halendar (BJH) theory. The BET surface area was analyzed by the adsorption amount of nitrogen gas adsorbed according to partial pressure (0.01 <p / p ₀ <1) using ASAP 2010 instrument of Micrometrics.

division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Surfactant (mL) One 2 3 5 2 2 Stirring Speed (rpm) 600 600 600 600 400 800 Tap Density (g / cm ³ ) 0.080 0.085 0.070 0.0946 0.086 0.085 Porosity (%) 96.4 96.4 96.5 95.7 96.1 96.0 Pore volume (cm ³ / g) 3.0 2.90 3.12 2.98 3.29 3.17 Average pore diameter (nm) 11.0 11.0 11.6 10.8 12.3 11.9 BET surface area (m ² / g) 700 704 720 693 726 722

As shown in Table 1, the tap density, porosity, pore volume, pore diameter and BET surface area are about 0.08 g / cm ³ , 96%, 3.0 cm ³ / g, 11 nm, and 700 m ² / g, respectively. It can be seen. The prepared airgel granules show very high pore volume and BET surface area. In addition, it can be seen that the surfactant forms stable and uniform silica sol droplets, and the surfactant did not affect the wet gelation and the connection structure of the silica.

In addition, the structure of the spherical silica airgel granules prepared in Examples 1 to 6 was observed with an optical microscope and a field emission scanning electron microscope (FESEM, S-4200, Hitachi, Inc.) and the results are shown in FIGS.

1 shows Examples 1 to 6 (Example 1 (a), Example 2 (b), Example 3 (c), Example 4 (d), Example 5 (e), and Example 6 (f)). The optical microscope observation photograph of). From the results of (a) ~ (d) it can be seen that the size of the granules decreases as the amount of the surfactant is increased. This result shows that the size of the silica sol droplets dispersed in n-hexane can be controlled by the amount of the surfactant. In addition, when comparing (b) and (e), it can be seen that the stirring speed of the n-hexane solution also affects the granule size, but between (b) with a stirring speed of 600 rpm and (f) with 800 rpm. In view of the fact that there is no difference, it can be seen that even if the stirring speed is increased above a certain speed, the benefit of the effect is not large.

2 is a field emission scanning electron microscope of Examples 2 to 6 (Example 2 (b), Example 3 (c), Example 4 (d), Example 5 (e), and Example 6 (f)). It is a photograph. All of the silica airgel granules of Examples 2 to 6 all have a three-dimensional connection structure with high porosity, and it can be seen that the granules and the pore structure are uniformly formed.

In addition, the FT-IR spectra of the spherical silica airgel granules of Examples 2 to 4 (Example 2 (b), Example 3 (c), and Example 4 (d)) were prepared by FT-IR spectroscopy (FTS-165). , Bio-Rad, Inc.) was used to analyze the wave number of 400 ~ 4000 cm ^-1 (wave number), and the results are shown in FIG.

Si-OH groups on the surface of the wet gel reacted with Si- (CH ₃ ) ₃ groups of trimethylchlorosilane to form hydrophobic Si-O-Si (CH ₃ ) ₃ groups through the surface modification process to hydrophobize the surface. It can be seen from FIG. The absorption peaks appearing near 1100, 1220, 800, and 460 cm ⁻¹ represent the structure of the silica airgel network of Si—O—Si. The absorption peaks appearing near 2900, 1260, and 850 cm ⁻¹ represent Si—CH ₃ termini modified by trimethylchlorosilane. The peak of the Si-CH ₃ group was not affected by the change in the content of the surface modifier. This is a result showing that the surface modifier does not affect the hydrophobization process of the airgel. In addition, the absorption peak by Si-OH bond was not shown in FIG. 3, which shows that the surface of the airgel was completely hydrophobized by trimethylchlorosilane.

Claims (8)

Adding a water glass solution to an ion exchange resin to obtain silica sol from which sodium ions have been removed;
n-hexane / silica sol mixed solution by adding at least one surfactant selected from silica sol, sorbitan monooleate, sorbitan monostearate, sorbitan monopalmitate and sorbitan monolaurate Preparing a;
Stirring the n-hexane solution at 400 to 800 rpm to form silica sol droplets;
Wet gelling the silica sol droplets by adding ammonia to the n-hexane solution;
Adding the wet gel to an n-hexane solution containing a silylating agent to hydrophobize the wet gel surface; And
Drying the hydrophobized wet gel;
Spherical silica airgel granules manufacturing method comprising a.
delete The method of claim 1, wherein the volume ratio of the silica sol and the surfactant is 1: 0.1 ~ 0.5 spherical silica airgel granules manufacturing method characterized in that.
According to claim 1, wherein the spherical silica airgel granules manufacturing method characterized in that the pH is adjusted to 5-7 when ammonia is added to the n-hexane solution.
The method of claim 1, wherein the volume ratio of the n-nucleic acid solution containing the silylating agent to the wet gel is 1: 1 to 4 characterized in that the spherical silica airgel granules manufacturing method.
The method according to claim 1, wherein the concentration of the silylating agent in the n-nucleic acid solution is 5 to 10% by volume.
Spherical silica airgel granules having a particle size of 100 ~ 1000 ㎛ prepared by the method of any one of claims 1 to 6.
The spherical silica airgel granules according to claim 7, wherein the silica airgel has a specific surface area of 650 to 750 m ² / g.

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