Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Reexamination Certificate
2001-11-13
2004-02-24
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C423S335000
Reexamination Certificate
active
06696036
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the extraction of silica from rice bran, and more particularly, to a method for extracting high purity amorphous silica or solid silica from rice bran which is harmless to the environment, of which a by-product from rice bran can be utilized.
BACKGROUND ART
An invention directed to a method for extracting amorphous silica has been filed in China (Chinese Patent Application No. 86-104705), and granted to a patent in India under registration No 159017, and also issued as a Russian patent No. 2061656.
The purity of the silica produced by using the above method is about 82~99.9%, which purity is, however, not suitable for silica in demand in the semiconductor field.
As for the silica produced by the above methods, since the content of coke that remains after burning the rice bran is high, it makes it impossible to obtain a high purity silica.
In addition, when rice bran is burned, soot is discharged, and about 32% CO and CO
2
are contained in the smoke from burning rice bran, which is harmful to the environment.
Meanwhile, Korean patent publication No. 97-5090 discloses a method for extracting silica without deforming the structure of silica formed during a growth period of rice by processing rice bran or rice straw with an enzyme and a method for adjusting the silica-carbon ratio by controlling the amount of enzyme and a reaction time.
However, the disclosed methods are directed to the matter of the silica structure, and a residual carbon amount is more than 14 wt %, very high, without description of any method for extracting a high purity silica as required in the present invention.
Moreover, Korean patent publication No. 97-5090 reveals that a Chinese Patent (CN 1,039,568) and a Russian Patent (SU 1,699,918) disclose a method for burning rice bran after processing in acid at a temperature of 700~900° C. to destroy the cellulose crystallization, but without mentioning any method for fabricating a high purity silica from rice bran which are washed with an acid solution, dehydrated under pressure and then burned in a second step, as in the present invention.
Furthermore, Russian Laid-Open Publication No. 94031518 A1 of Jul. 10, 1996, German Laid-Open Publication No. 1532398A of Nov. 15, 1978, a French Laid Open Publication No. 2356595 A1 of Mar. 3, 1978 also disclose a method in which rice bran is sieved to remove impurities, washed with water, washed in an acid solution, dried, burned and pulverized. The silica product obtained by this method has a purity of 99.0~99.5%, but by-products of phytine, phytic acid (C
6
H
6
[OPO(OH)
6
] and xylitol (CH
2
OH(CHOH)
3
CH
2
OH) are generated from the soot.
Accordingly, a method for producing high purity silica, which is capable of easily obtaining silica of 99.99% purity, increasing the purity of a silica product by discharging soot generated as a by-product during a burning process of rice bran by using a fan, separating phytic acid and xylitol included in supernatant of a storage tank in which soot has been filtered to be removed, solving an environmental pollution problem due to the by-products by utilizing the soot settled at the bottom of the storage tank as an antiseptic solution, and obtaining a useful product, is highly demanded.
Therefore, an object of the present invention is to provide a method for extracting silica of 99.99% purity from rice bran, which is capable of removing soot, a by-product harmful to the environment, to increase the purity of the silicon product and producing a useful product from the soot.
DISCLOSURE OF INVENTION
In order to achieve the above objects, there is provided a method for extracting silica of more than 99.99% purity from rice bran including: the steps of: (a) pretreating rice bran by washing rice bran and removing impurities floated on the water; (b) sequentially washing the rice bran in an acid solution and water at least twice; (c) dehydrating the washed rice bran under pressure; (d) drying the dehydrated rice bran; (e) priomarily burning the dried rice bran at a temperature of 350~400° C. while agitating and pulverizing; and (f) secondarily burning the rice bran at a temperature of 700~1000° C. for 10~60 minutes while agitating by providing oxygen or air.
BEST MODES FOR CARRYING OUT THE INVENTION
The present invention provides a method for extracting silica of 99.99% purity which is capable of effectively removing soot, a by-product, and obtaining a useful chemical product from such by-product.
In detail, the method for extracting silica of 99.99% purity includes a pre-treatment step (a) in which rice bran is sieved to remove impurities and washed in water to remove impurities floated on the water; a washing step (b) in which the rice bran is sequentially washed in an acid solution diluted with distilled water and then in distilled water at least twice; a step (c) in which the washed rice bran is dehydrated under pressure; a step (d) in which the dehydrated rice bran is dried; a first burning step (e) in which the dried rice bran is burned at a temperature of 350~400° C. while being agitated and pulverized; a second burning step (f) in which the rice bran is burned at a temperature of 700~1000° C. for 10~60 minutes while being agitated by providing oxygen or air.
The processes for extracting high purity silica from rice bran will now be described in more detail.
(a) Pre-Treatment Step:
A quantity of rice bran is sieved to filter out waste matter and then washed in water. At this time, impurities floated on the water are removed. During the washing process, most impurities are removed. These impurities being removed at this time are hardly removed even at a second burning step wherein the rice bran is treated at the high temperature of 700~1000° C., remaining in silica. Thus, removal of the impurities in the washing process is very critical. During the washing process, if the impurities floated on the water are not removed and then the moisture is removed when extracting silica, the finally obtained silica would have a low purity.
During the washing process, the rice bran may be washed in cold water. But when washed in hot water at 85~95° C., the impurities are more effectively removed. In the case of using hot water at 85~95° C., the rice bran is washed by being continuously agitated. Use of hot water disadvantageously incurs a higher production cost. Thus, the combined use of cold water and hot water may be possible in consideration of economical efficiency and desired purity. The water used may be ordinary water, but distilled water is preferred in view of the purity of the obtained silica and the follow-up processes.
In one embodiment of the present invention, if the rice bran is washed in boiling water, that is, boiling water at a temperature of 100° C., for 30 minutes to 120 minutes, since the bubbles generated when water is boiled agitate the rice bran, the rice bran can be advantageously washed without using an additional agitator. Accordingly, as the time period is reduced from 120 minutes to 30 minutes, the purity of the silica is heightened. In addition, in case of washing the rice bran in boiling water, the water obtained after the rice bran is washed includes much phytic acid and xylitol component while the washed rice bran have less organic substances. And soot is reduced, and in case of discharging gas, less poisonous gas (CO, NO
2
) is contained therein.
Before washing the rice bran in an acid solution, a process in which the structure of the rice bran is changed to facilitate removal of organic substances may be arbitrarily added. That is, if the washed rice bran is left at a temperature of −10~−140° C. for 10~300 minutes, the final purity of the silica is heightened.
As the liquid contained in the rice bran is frozen, the structure of the rice bran is broken, changing to a form which is easily broken. Thus, after the freezing process, when the rice bran is washed in an acid solution, the organic substances contained in the rice bran can be more easily and quickly removed.
In order to freeze the rice bran
Alexandre Bylkov
Victor Dmitri
Victor Vinogradov
Birch & Stewart Kolasch & Birch, LLP
Johnson Edward M.
RK Chemical Co., Ltd.
Silverman Stanley S.
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