KR20080099819A - Process for synthesizing nanosize silica particles - Google Patents

Abstract

A method for synthesizing nano-sized silica particles is provided to obtain silica having a particle size of 50-800nm. A method for synthesizing nano-sized silica particles comprises the following steps of adding sodium silicate is added to HCl of 0.1-0.3N so that pH can be within a range of 3-7, in the room temperature and precipitating silica gel; removing NaCl components by washing/filtering precipitated silica gel; and By using the bead mills, the silica gel from which the NaCl components is removed is pulverized at a pulverizing speed of 2000-6000rpm so as to become particles of nano size.

Description

Process for Synthesizing Nanosize Silica Particles

The present invention relates to a method for producing silica of nano-sized particles. More specifically, the present invention relates to a method for producing silica of nano-sized particles that can easily control the process conditions by disintegrating secondary silica particles using a disintegration apparatus.

With the recent advance in industrial technology, much attention has been drawn to the manufacturing method of various metal and nonmetal particles having nano size. In particular, research has been conducted to produce silica into fine particles, but it is still difficult to apply to mass production of silica of nano-size particles, in particular, nano-size particles of silica, in terms of economy and efficiency. Therefore, there is an urgent need for a simple and economical method for producing nano-sized particle silica.

The most common method for preparing nano-grade silica is to prepare silicon dioxide fine powder by the reaction of Scheme 1 by oxidizing silicon tetrachloride (SiCl ₄ ) at high temperature.

Scheme 1

SiCl ₄ ---> SiO ₂ + 2Cl ₂

However, the most chronic and fatal drawbacks of the existing methods are that silicon tetrachloride is very expensive and that the process produces highly corrosive and environmentally dangerous chlorine gas. For this reason, when constructing a process system, a huge cost is required. In addition, since the price of silicon tetrachloride as a raw material is about 10 times that of water glass used as a raw material in the present invention, there is a problem that the price of the manufactured product is expensive. However, in the current industry only 100 billion nano-scale silica is required, the situation is increasingly used, the production of silica of cheaper nano-size particles is urgently required.

In this regard, the present inventors have proposed a method for producing silicon oxide to remove water in silica produced from water glass using water glass as a raw material and butanol (n-Butanol) in Korean Patent Application No. 2002-10086. In the Korean patent application 2002-10086, silica is prepared by using water glass as a raw material to form fine silica by adjusting the pH of a solution to a very narrow and accurate value, and removing water in silica using butanol. Although the manufacturing method is effective, it has a problem in terms of technical and economical efficiency because it is very difficult to meet the process reaction conditions when applied to the actual process. In addition, the distillation method is used at a high temperature of more than 100 ℃ in the step for removing the moisture of the silica, the high temperature distillation method is efficient to remove the moisture without the agglomeration of very fine silica powder compared to the simple spray fluidized bed drying method, but in the mass production process In application, the distillation apparatus is too complex and takes a long time. In addition, using a butanol organic solvent has a disadvantage in that the production process for the use and recovery of the organic solvent is complicated and the production cost is increased due to the inevitable loss of the organic solvent.

In addition, a method of preparing silica by forming silica using water glass as a raw material and removing moisture from silica formed using butanol (n-Butanol) or a propanol organic solvent is disclosed in Korean Patent Application 2004-72143. Unlike Korean Patent Application No. 2002-10086, Korean Patent Application No. 2004-72143 removes moisture in wet silica without agglomeration of particles by contacting wet silica and organic solvent several times at room temperature. The method of Korean Patent Application No. 2004-72143 is performed at room temperature because the water removal step is performed at room temperature, but the process is simpler and the manufacturing process time can be shortened. However, a large amount of organic solvent is used compared to the distillation method. There is a problem that the organic solvent is lost due to the contact of the solvent.

The conventional method for producing silica of nano-sized particles has a disadvantage in that the process is complicated and the organic solvent is lost due to the use of the organic solvent. In addition, the patent applications must adjust the pH to a very narrow range in order to produce silica from water glass, so it is difficult to uniformly and accurately adjust this narrow pH range in a practical process using a very large reactor.

Accordingly, an object of the present invention is to provide a method for producing silica of nano-sized particles more simply and economically.

Another object of the present invention is to provide a method for producing silica of nano-sized particles which can more easily control the silica formation reaction conditions.

Still another object of the present invention is to provide a method for preparing silica of fine and fine nano-sized particles.

According to the invention,

a) precipitating silica gel by adding sodium silicate to pH 3-7 at 0.1-0.3 N HCl at room temperature;

b) washing and filtering the precipitated silica gel to remove the NaCl component;

c) disintegrating the silica gel from which the NaCl component is removed into nano-sized particles using a bead mill at a disintegration rate of 2000-6000 rpm; And

d) drying the silica slurry obtained after disintegration;

Provided is a method for preparing silica of nano-sized particles comprising a.

In the silica production method of the nano-sized particles according to the present invention, water glass is used as a raw material, and since an organic solvent is not used, it is safe, economical, and easy to process. In addition, it is easy to control the process conditions can be easily applied to the mass production process, it is possible to efficiently manufacture the silica of nano-sized particles in a continuous process and / or an automated system. Furthermore, silica of particles size of 50-800 nm is obtained by the method of the present invention, and fine nano-sized particles of silica can be usefully used in various high-tech industries.

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

The present invention not only enables the formation of fine and uniform fine silica gel particles in the process of changing from low pH to high pH by adding silica to hydrochloric acid when forming silica gel, but also fine and fine silica gel by process control to disintegrate the aggregation of such fine silica gel particles. The present invention relates to a method for producing silica of nano-sized particles to obtain particles.

The method of the present invention is economical because inexpensive water glass is used as a raw material and no organic solvent is used, and the process is simplified. 1 shows a process for producing silica of nano-sized particles according to the present invention. Hereinafter, a method for preparing nano-sized particle silica according to the present invention will be described with reference to FIG. 1.

In the method for preparing nano-sized particle silica according to the present invention, first, water glass (sodium silicate) is added to hydrochloric acid of 0.1-0.3N at room temperature to pH 3-7, preferably pH 3-6 to form silica gel. In the present invention, by adding water glass to hydrochloric acid, silica gel particles are formed during the process of changing from low pH to high pH, and the silica gel particles produced under such pH changing conditions are formed in the form of semi-transparent fine and fine particles. When the concentration of hydrochloric acid is less than 0.1N, the concentration of the produced silica gel is so low that the yield is too small compared to the process scale, and when the concentration of hydrochloric acid exceeds 0.3N, the concentration of hydrochloric acid is so high that the silica gel is formed rapidly. The reaction does not proceed uniformly, and thus is not preferable because it is not uniform and thick airgel is formed. If the pH is less than 3, the silica gel itself is not formed in the solution, which is not preferable. If the pH is above 7, the yield of conversion of the silica component into the silica gel is lowered, which is not economical, and a uniform and thick airgel is formed. This is undesirable. As the water glass used as the raw material of the silica, a purified one can also be used. It is advantageous to bring the pH closer to 3 in order to polymerize to finer silica particles. In this case, the water glass may be diluted and used so that it may be more easily and uniformly mixed as necessary.

As described above, in the method according to the present invention, the silica gel forming step is performed at room temperature, and water glass is added to pH 3-7 in 0.1-0.3N hydrochloric acid so that fine and fine silica particles are formed uniformly. Since the pH range controlled in the silica gel forming step is wide, it is easy to control the reaction conditions when applied to the actual process, and thus can be easily applied to the mass production process.

The silica gel formed under the reaction conditions as described above forms primary coarse silica particles when the silica gel is formed to form coarse secondary silica particles. It can be prepared as.

As described above, water glass is added to hydrochloric acid to pH 3-7, and silica gel is precipitated by mixing hydrochloric acid and water glass. The precipitated silica gel is washed and filtered to remove NaCl component from the precipitated silica gel. Washing may be performed using water or distilled water, if necessary. Filtration can be performed using a centrifugal filtration apparatus etc. as shown in FIG.

Silica gel obtained by removing NaCl is obtained as a secondary particle aggregate in which primary particles are agglomerated due to relatively wide pH conditions. Thus, the silica gel, which is a secondary particle aggregate, is disintegrated in order to prepare nanoparticles of silica.

Disintegration may be performed using a disintegration apparatus, specifically, a bead mill. The obtained silica gel is introduced into the disintegrating apparatus as silica gel in a slurry state diluted with water. At this time, the silica gel is diluted so that the content of silicon oxide (SiO ₂ ) is 1-10% by weight. If the silicon oxide component is less than 1% by weight, the amount of silica processed per unit process is too small, which is undesirable from an economical point of view, and if it exceeds 10% by weight, the viscosity of the silica slurry is too high, which is not preferable in that it is not easy to input raw materials. not.

At the time of disintegration, zirconia beads and / or silica beads may be used as beads in the bead mill. It is desirable to use silica beads for complete contamination protection. However, silica beads are weak in strength compared to zirconia beads and wear quickly, which is disadvantageous in terms of cost. As silica and / or zirconia beads, it is preferable to use beads having a particle diameter of 0.1 mm to 0.3 mm. If the particle diameter of the beads exceeds 0.3mm, it is difficult to obtain silica having a particle size of less than 800 nm, and if the particle size is less than 0.1mm, the beads are too small, making it difficult to recover the beads after use and increasing the loss rate. Disintegration is preferably performed at a speed of 2000 rpm to 6000 rpm. If it is less than 2000rpm, the speed is too slow to disintegrate properly. Therefore, the silica particles are fine and not disintegrated properly.If it exceeds 6000rpm, it is advantageous to disintegrate, but the faster the speed, the bead wear only increases, and at about 6000rpm. Silica can be sufficiently disintegrated into fine particles, and does not necessarily require disintegration at speeds in excess of 6000 rpm. Since the secondary silica particles are not disintegrated into nano-sized particles in one disintegration, they are repeatedly disintegrated until silica of the desired nano-sized particles is obtained. Although not limited thereto, for example, when disintegrating at 2000rpm-6000rpm using beads having a particle diameter of 0.1mm-0.3mm, silica of nano-sized particles can be obtained by disintegrating about 4-8 times. If less than 4 times, the silica particles are not sufficiently disintegrated to the nanoscale, and if more than 8 times, they are sufficiently disintegrated and do not need further disintegration.

In the disintegration step, the silica gel in the aggregated state of the secondary particles is disintegrated in nano size. The silica gel is disintegrated in the disintegration step to change into a slurry which is slightly diluted than the gel state. Silica gel in the slurry state obtained in the disintegration step is dried to obtain nano-sized particles of silica. As shown in FIG. 1, drying can be performed in a fluidized bed drying apparatus, specifically, a bottom injection type fluidized bed drying apparatus or an upstream injection type drying system. A fluidized bed dryer or an upstream jet drying system is a device that blows up moisture instantaneously by hot air by spraying slurryed silica with high pressure through a number of uniform and fine nozzles at the bottom. At this time, the temperature of hot air is 120 degreeC or more, Preferably 120 degreeC-200 degreeC is suitable. If the temperature is less than 120 ° C, the temperature is too low to dry sufficiently, and if it exceeds 200 ° C, the drying is good, but it is uneconomical and does not require a temperature exceeding 200 ° C. As shown in FIG. 1, for example, a silica slurry is continuously injected into the drying apparatus (fluid-bed dryer), and the powder is collected by a cyclone from the top, and then the powder is collected using a bag filter. . The evaporated solvent can then be taken up in a condenser system (not shown in FIG. 1) equipped with a cooler.

After the drying, nano-sized silica can be obtained as a powder in the form of particles. Such nanosilica particles are then preferably further heat treated at 285 ° C or higher. Some of the nano silicas obtained after drying are chemically present in the form of SiO ₂ · H ₂ O, and when these types of silica particles are exposed to air for an extended period of time, aggregation of particles may be caused by water molecules crystallized together. This phenomenon is undesirable for the commercialization of very fine nanoscale silica particles. Therefore, it is preferable to remove the crystallized water molecules contained in the silica by heat-treating the nanosilica obtained by drying at 285 ℃ or more. It is preferable to perform heat processing at 285-500 degreeC. If the heat treatment temperature is lower than 285 ° C., the SiO ₂ · H ₂ O form may not be completely converted to the SiO ₂ form, which is undesirable in that the above-mentioned agglomeration may occur. It is not preferable in that it can be done. Further, the heat treatment is performed for 2 hours or more, preferably 2-4 hours. If the heat treatment time is less than 2 hours, the SiO ₂ · H ₂ O form may not be sufficient to completely convert to the SiO ₂ form, and if it exceeds 4 hours, it may consume unnecessary energy in terms of economy. Not desirable in

By the heat treatment as described above, all the silica particles are present in the form of chemically stable SiO ₂ , so that even when exposed to air for a long time, particle aggregation is prevented, thereby increasing the value as a commodity.

The silica according to the present invention is obtained by the method according to the present invention as described above. The obtained silica has a particle size of about 50-800 nm, and such fine nano sized silica can be usefully used in various high-tech industries. For example, it may be used in admixture with rubber, plastic paper, etc. as an additive mainly for improving strength and physical properties. It can also be used in the synthesis of dyes, pesticides, inks and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention.

Example 1

(1) Preparation of silica gel by adding water glass to low concentration hydrochloric acid

Silica gel was formed by adding water glass (water glass diluted approximately 1.5 times with distilled water to about 325 ml of 40Be water glass having a concentration of 40Be of SiO ₂ / Na ₂ O = 3.0) to 325 ml of 0.3N HCl to pH 6. The silica gel picture formed in this case is shown in FIG. 2 and the electron micrograph is shown in FIG. 3, and the silica gel formed was very fine, uniform and translucent as shown in FIG. 2. On the other hand, as can be seen in the electron micrograph of Figure 3, it could be confirmed that the fine silica gel particles of several hundred nanometers are entangled with each other.

(2) Preparation of silica gel by adding high concentration hydrochloric acid to water glass

Silica gel was formed by adding 40Be water glass to 325 ml of 2N hydrochloric acid to pH 10. Photographs of the formed silica gel are shown in FIG. 4 and electron micrographs are shown in FIG. As can be seen in Figure 4, the resulting silica gel particles were found to be very opaque and completely opaque. In addition, as can be seen in the electron micrograph of Figure 5, it was confirmed that the silica gel particles are very rough and large compared to Figure 3 of Example 1 (1).

As such, when a high concentration of hydrochloric acid outside the scope of the present invention is used or when the pH range of the reaction of water glass and hydrochloric acid is outside the scope of the present invention, a very rough and large silica gel particle is formed. Is not effectively disintegrated into nano-grade particles even when disintegrated. Therefore, in this case, not only disintegration but also grinding, it is difficult to manufacture the nano-scale particles, and also has the disadvantage of requiring excessive cost, time and energy.

Example  2

In this embodiment, the change in particle size of the silica according to the repeated disintegration cycle is demonstrated. To about 325 ml of 0.3 N HCl was added about 700 ml of water glass (water glass with a concentration of 40Be of glass containing 40 mL concentration of SiO ₂ / Na ₂ O = 3.0 in distilled water at 1.5 times) to pH 6, and thus silica gel. Was formed. At this time, the silica gel is washed 6-7 times with sufficient water to wash the NaCl formed together. The washed silica gel is added to 4 L by adding water to a suitable concentration for disintegrating. It contains about 4% by weight (160g) of substantially pure silica (SiO ₂ ). The silica in this slurry state has an average particle size of 30-40 µm, which is disintegrated using 0.1 mm zirconia beads.

At this time, the silica slurry input flow rate was 100 ml / min and the disintegration rate was 4000 rpm. At this time, while performing the repeated disintegration cycle from 1 to 8 times, the particle size of the disintegrated silica in each case was analyzed and shown in FIGS. 6 to 13.

As can be seen in Figures 6 to 13, when the disintegration at 4000rpm disintegration rate of four or more times, it can be seen that the silica of the micro-class almost disappears and mostly exist as the average of 200-300nm class silica.

Example  3

To about 325 ml of 0.2 N HCl, about 700 ml of water glass (water glass with a concentration of 40Be of SiO ₂ / Na ₂ O = 3.0 diluted 1.5 times with distilled water) was added to pH 6, thereby forming silica gel. It became. At this time, washing with sufficient water 6-7 times to wash the NaCl formed together. Before the washed silica gel is added to the disintegration apparatus, water is added to make 16 L to prepare a solution containing approximately 1.1 wt% of pure silica (SiO ₂ ). The silica in this slurry state had an average particle size of d _{50 =} 30.354 μm, which was disintegrated eight times using 0.3 mm zirconia beads. Silica slurry input flow rate was 100ml / min and disintegration rate was 2000rpm and 4000rpm, respectively. The disintegrated silica slurry is dried in a bottom spray type fluid bed dryer having a hot air temperature of 150 ° C. to recover the powder as shown in FIG. 1. The silica slurry was continuously injected into a fluidized bed drier and dried, after which the powder was first collected in a cyclone from the top and then collected using a bag filter. The evaporated solvent was obtained in a condenser system equipped with a cooler. The d ₅₀ size of the recovered silica powder is shown in FIG. 14. In this case, the average particle size of silica did not disintegrate below d ₅₀ = 748 nm even after 9 times of disintegration.

1 is a view showing a silica manufacturing process of nano-sized particles according to the present invention,

2 is a photograph of silica gel prepared in Example 1 (1),

3 is an electron micrograph of the silica gel prepared in Example 1 (1),

4 is a photograph of silica gel prepared in Example 1 (2),

5 is an electron micrograph of the silica gel prepared in Example 1 (2),

FIG. 6 is a particle size distribution analysis result of silica obtained by disintegrating silica gel having an average size of 30-40 μm in slurry state at a time of 0.1 ml zirconia beads at 100 ml / min of silica slurry flow rate and 4000 rpm of disintegration rate. Is a graph showing

7 is a particle size distribution analysis result of silica obtained by disintegrating silica gel having a slurry size of 30-40 μm on average using 0.1 mm zirconia beads twice at a silica slurry input flow rate of 100 ml / min and a disintegration rate of 4000 rpm. Is a graph showing

FIG. 8 is a particle size distribution analysis result of silica obtained by disintegrating silica gel having a slurry size of 30-40 μm on average using 0.1 mm zirconia beads three times at a silica slurry input flow rate of 100 ml / min and a disintegration rate of 4000 rpm. Is a graph showing

FIG. 9 is a particle size distribution analysis of silica obtained by disintegrating silica slurry in an average slurry size of 30-40 μm using 0.1 mm zirconia beads at a rate of 100 ml / min of silica slurry and 4 times of disintegration rate of 4000 rpm. Is a graph showing the results,

FIG. 10 is a particle size distribution analysis of silica obtained by disintegrating silica slurry in a slurry state of average size of 40-40 μm using 0.1 mm zirconia beads at a rate of 100 ml / min of silica slurry and 5 times of disintegration rate of 4000 rpm. Is a graph showing the results,

FIG. 11 is a particle size distribution analysis of silica obtained by disintegrating silica slurry in a slurry state of average size of 40-40 μm using 0.1 mm zirconia beads at a rate of 100 ml / min of silica slurry and 6 times of disintegration rate of 4000 rpm. Is a graph showing the results,

FIG. 12 is a particle size distribution analysis of silica obtained by pulverizing silica slurry at a flow rate of 100 ml / min and disintegration rate of 4000 rpm using 0.1 mm zirconia beads in an average silica gel of 30-40 μm in Example 2. Is a graph showing the results,

FIG. 13 is a particle size distribution analysis of silica obtained by disintegrating silica slurry in a slurry state of average size of 40-40 μm using 0.1 mm zirconia beads at a rate of 100 ml / min of silica slurry and 8 times of disintegration rate of 4000 rpm. Is a graph showing the results,

14 shows that in Example 3, silica slurry in the form of a slurry having an average particle size of d ₅₀ = 30.354 µm was pulverized using a 0.3 mm zirconia bead at a slurry dissolution rate of 100 ml / min and disintegration rates of 2000 rpm and 4000 rpm, respectively. It is a graph which shows the particle size distribution analysis result of the obtained powder after drying by drying by fluidized-bed drier of ° C.

Claims (8)

a) precipitating silica gel by adding sodium silicate to pH 3-7 at 0.1-0.3 N HCl at room temperature; b) washing and filtering the precipitated silica gel to remove the NaCl component; c) disintegrating the silica gel from which the NaCl component is removed into nano-sized particles using a bead mill at a disintegration rate of 2000-6000 rpm; And d) drying the silica slurry obtained after disintegration; Silica production method of the nano-size particles comprising a. The method of claim 1 wherein the bead mill is at least one selected from the group consisting of zirconia beads and silica beads. 2. The method of claim 1, wherein the bead mill uses beads having a diameter of 0.1-0.3 mm. The method of claim 1, wherein the silica gel introduced in the disintegration step is a silica gel diluted to a content of 1-10% by weight of the silicon oxide (SiO ₂ ) component. The method according to claim 1, wherein the disintegration step is repeated until silica of nano-sized particles is obtained. The method of claim 1 wherein said drying step is performed using a fluidized bed drying system or an upstream spray drying system at 120-200 ° C. The method of claim 1, further comprising heat treatment at 285-500 ° C. after the drying step. 8. The method of claim 7, wherein said heat treatment step is performed for 2-4 hours.

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