Patent Application
20080085232
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.
In preparing silica nanoparticles from siliceous mudstone, an integrated process technology, comprising compounding sodium silicate; preparing a silicate aqueous solution; and preparing silica nanoparticles, will be described with reference to the drawings.
Below, the aforementioned processes will be described in detail.
The method of preparing silica nanoparticles from siliceous mudstone comprises: solving a silica constituent into a sodium silicate constituent by a leaching reaction of the siliceous mudstone, using a sodium hydroxide aqueous solution (S100); performing ion exchange to remove a sodium constituent from the sodium silicate constituent, thereby preparing a silicate aqueous solution (S200); and performing flame spray pyrolysis to prepare silica nanoparticles with the average particle dimension being in within a range of 9 to 57 nanometers(nm) from the silicate aqueous solution (S300).
Prior to Step S100, the method of preparing silica nanoparticles further comprises: performing heat-treatment to remove a water constituent contained in the siliceous mudstone (S50); and performing a leaching action using hydrochloric acid to remove impurities contained in the siliceous mudstone (S60). At the solving of the silica constituent into sodium silicate at S100 after the impurities of the siliceous mudstone are removed at S60, as a reaction temperature increases from 25° C. to 100° C., extraction efficiency increases from 23% to 83%.
At the solving of the silica constituent into sodium silicate at S100, as a reaction time increases from 15 min. to 90 min. at a reaction temperature of 100° C., a leaching rate of the silica constituent increases.
At the performing of the ion exchange to remove the sodium constituent thereby preparing the silicate aqueous solution at S200, the ion exchange is an ion-exchange resin method using cation exchange resin, and the silicate aqueous solution is formed to contain the concentration of sodium being 50 ppm or less by passing an ion-exchange resin layer of a sodium silicate aqueous solution at a linear velocity of 2.0 to 0.5 cm/sec.
At the performing of the flame spray pyrolysis to prepare silica nanoparticles from the silicate aqueous solution by a flame reaction (S300), a flame reactor including five pipes is used, with a first tube through which the silicate aqueous solution, which is aerosolized by high-pressure spraying a dispersed air in a proportion of 1 to 3% by volume of a flow quantity of the whole gas, is injected; a second tube into which an argon gas flows by 7 to 8%; a third tube into which a hydrogen gas flows by 3 to 14%; a fourth tube into which an oxygen gas flows by 21 to 24%; and a fifth tube into which an air flows by 55 to 63%. As the pressure of the dispersed air, which is supplied for aerosolizing the reaction solution of the first tube, varies within a range of 0.5 to 2.0 kgf/cm2, the average particle dimension of the silica nanoparticles is controlled.
Various embodiments of the present invention will be described as follows.
Exemplary Embodiment 1 relates to the preparation of the sodium silicate aqueous solution as the first process for preparing silica nanoparticles from siliceous mudstone.
The siliceous mudstone used in the experiment is amorphous silica minerals. The siliceous mudstone includes the silica content of about 70% and a great quantity of organic matter and water in a natural state. When the siliceous mudstone is heat-treated at 800° C., the composition of a silica component increases to 90%, and aluminium and iron constituents as impurities are respectively present as 6.83% and 1.18% in the form of oxides.
For the experiment of a change in the leaching time, the siliceous mudstone is powdered to be in the average particle dimension of 9 micrometer (μm) and is leached to process the impurities, using a hydrochloric acid aqueous solution in the concentration of 110% of the required amount of hydrochloric acid, at a reaction temperature of 100° C. As a result, iron and aluminium are respectively removed as 75% and 55%. From the siliceous mudstone from which the impurities are removed, the sodium silicate aqueous solution is prepared through the leaching experiment using the sodium hydroxide aqueous solution. The reaction temperature and the reaction time are selected as main variables for the experiment. The reaction temperature is changed from 25 to 100° C., and the reaction time is changed from 15 to 90 minutes.
Exemplary Embodiment 2 relates to the preparation of the silicate aqueous solution from the sodium silicate aqueous solution prepared during the first process, by removing the sodium constituent by the ion exchanging resin, as the second process for preparing silica nanoparticles from siliceous mudstone.
The ion-exchange resin relating to the adsorption of Na+ by the cation exchange resin is described as the following formula:
Resin−H++Na++SiO32−→Resin−Na++H++SiO32−
The cation exchange resin is in the form of hydrogen, and the pH range to be used is 0 to 14. An ion-exchange resin column is prepared with the capacity being 5 cm in diameter and 80 cm in height. The sodium silicate aqueous solution prepared in Exemplary Embodiment 1 is a strong alkali solution with the pH of about 14. As a result of passing the sodium silicate aqueous solution in the column, changing the linear velocity to 2.0., 1.5, 1.0, and 0.5 cm/sec, the amount of residual sodium in the silicate aqueous solution as processed decreases to 50, 30, 20 and 10 ppm, respectively.
Exemplary Embodiment 3 relates to the preparation of silicate nanoparticles from the silicate aqueous solution prepared in Exemplary Embodiment 2, by flame spray pyrolysis, as the last process for preparing silica nanoparticles from siliceous mudstone.
The experiment of preparing silica nanoparticles is performed, by injecting the silicate aqueous solution into the flame formed under the following experimental conditions.
When the silicate aqueous solution is injected into an aerosol generator 10 in a dual fluid nozzle type as illustrated in
As for the flow quantity of gas flowing into the flame reactor including five tubes, the dispersed air is supplied to the first tube of the flame reactor, in a proportion of 2 to 3% by volume of the flow quantity of the whole gas, by changing its pressure to 0.5, 1.0, 1.4 and 2.0 kgf/cm2, so that the silicate aqueous solution being aerosolized at a molarity of 0.843 mol/l is introduced; the argon gas by 7% is flowed into the second tube; the hydrogen gas by 14% is flowed into the third tube; the oxygen gas by 21% is flowed into the fourth tube; and the air by 55 to 56% is flowed into the fifth tube.
As a result of examining the changes in the specific surface area and dimension of a particle by the specific surface area analyzer (BET method), as the pressure of the dispersed air increases to 1.0 kgf/cm2, 1.4 kgf/cm2, and 2.0 kgf/cm2, the specific surface area increases to 47 m2/g, 174 m2/g, and 294 m2/g. In a conversion formula (dp=6/(ρp·A), dp indicates the dimension of a particle, ρp indicates the density of silica, and A indicates the specific surface area. From this formula, the average particle dimension as calculated decreases to 57 nm, 15 nm, and 9 nm.
In accordance of the present invention, the method of preparing silica nanoparticles from siliceous mudstone comprises solving the silica constituent into sodium silicate by 80% or more, by the leaching reaction of siliceous mudstone; preparing the silicate aqueous solution, by removing the sodium constituent to 50 ppm or less by ion exchange; and preparing the silica nanoparticles with the average particle dimension of 57 nm or less by flame spray pyrolysis.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0098132 | Oct 2006 | KR | national |
