Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Reexamination Certificate
2001-04-10
2004-05-25
Nguyen, N. M. (Department: 1754)
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
C423S333000, C423S326000
Reexamination Certificate
active
06740300
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improved method for manufacturing a crystalline layered sodium disilicate and more particularly, to the improved method for manufacturing the crystalline layered sodium disilicate comprising the steps including the preparation of granules in a certain ratio of anhydrous sodium silicate cullet, a starting material, in the presence of some binders such as water and aqueous solution of sodium silicate, followed by a crystallization step of the granules, wherein a small amount of final product is recycled to the prior crystallization step in order to prevent the attachment of granules to an inner crystallization device, which occurs due to local sintering in a high-temperature crystallization condition of continual process and also to further enhance the unit productivity during the mass production of crystalline layered sodium disilicate.
2. Description of the Related Art
The term “cullet” used as a starting material of this invention, which has been frequently used as a raw material in a field involved in the manufacture of sodium silicate solution, refers to a compound in a small lump or piece derived from amorphous sodium silicate, prepared in such a manner that a mixture of silica and sodium carbonate in an appropriate molar ratio (ratio of SiO
2
O, to Na
2
O, namely SiO
2
/Na
2
O) is heated at the temperature of 1000-1400° C., melted and cooled.
In addition, the term “layered sodium silicate” refers to crystalline silica compounds expressed by “(Na
2
O)
x
(SiO
2
)
y
” (where y/x varies differently depending on the crystal structure and has the common values ranging from 2 to 11); among them, the crystalline layered sodium silicate expressed by Na
2
Si
2
O
5
is reported to have various crystal forms such as &agr;, &bgr;, &ggr; and &dgr;-phases and with its excellent adsorptivity and ion-exchange capacity originated from structural specificity, the crystalline layered sodium disilicate has been useful as a catalytic carrier or in a variety of chemical processes such as separation and purification. With its higher binding capacity on the hardness components in water such as Ca
2+
and Mg
2+
in particular, the crystalline layered sodium disilicate in &dgr;-phase, the crystalline layered sodium disilicate has been recently used as a water softener or detergent composition builder.
However, the process for manufacturing the crystalline layered sodium disilicate in &dgr;-phase has recognized some disadvantages in that severe foaming induced by a leakage of remaining water is generated in the initial crystallization step, and with sintering and shrinkage of particles, they are deposited in the crystallization device.
To comply with this matter, U.S. Pat. No. 5,211,930 has added a method for recycling 10-50 wt % of final product to the crystallization step, thus preventing deposit of products in a calcination device.
However, the above method has proven to be uneconomical with poor unit productivity during mass production, since a large amount (10-5 wt %) of final product is recycled to the device; the reduction of unit productivity cannot be overcome in a process where powders containing a large amount of water is fed.
Under such circumstances, in an effort to prevent the deposits of final product in the crystallization device, the inventor et al. in their respective patents (U.S. Pat. No. 5,567,404, its corresponding Korea Patent No. 13997 and Korea Patent Appln. No. 97-33207) have disclosed some methods for manufacturing the crystalline layered sodium disilicate in such a manner that water or aqueous solution of sodium silicate in a small amount for agglomeration is added to a cullet powder, a starting material, thereby preparing granules with a small amount of water and then the granules are crystallized in calcination furnace, thus ensuring more simplification of manufacturing process, reduction in energy consumption, and removal of deposits remaining in the device. Notwithstanding this, these methods have still failed to eliminate the deposits of some granules in the device during the crystallization step, when a continual process for mass production is operated.
SUMMARY OF THE INVENTION
To overcome the aforementioned shortcoming that reactants are deposited in a crystallization device, the inventor et al. have found that a process recycling a small amount of final product to the device may not only eliminate the deposit of product in a calcination furnace associated with local sintering occurring at a higher temperature during continual process, but also recycle less amount than that of the U.S. Pat. No. 5,211,930, thus resulting in significant increase of unit productivity during mass production. In consequence, the inventor et al. have completed this invention.
Therefore, an object of this invention is to provide an improved method for manufacturing a crystalline layered sodium disilicate, being characterized in that some defects found in the crystallization device have been completely removed by specifying the agglomeration and recycling steps for possible continual process, thereby improving unit productivity during mass production.
DETAILED DESCRIPTION OF THE INVENTION
This invention is characterized by an improved method for manufacturing crystalline layered sodium disilicate comprising the subsequent steps of a) preparing granules with the addition of water as binder to anhydrous sodium silicate cullet powder; b) drying and crystallizing the granules by heat calcination to prepare sodium disilicate, wherein 3-5 wt % of final product, sodium disilicate, is recycled to the prior crystallization step.
Also, this invention is characterized by an improved method for manufacturing the crystalline layered sodium disilicate comprising the subsequent steps of a) preparing granules with the addition of an aqueous solution of sodium silicate as binder to anhydrous sodium silicate cullet powder; b) drying and crystallizing the granules by heat calcination to prepare sodium disilicate, wherein 3-5 wt % of final product, sodium disilicate, is recycled to the prior crystallization step.
This invention is explained in detail as follows:
This invention relates to a method for manufacturing a crystalline layered sodium disilicate, performed in such subsequent steps that a certain amount of water or aqueous solution of sodium silicate is added to an anhydrous sodium silicate cullet powder comprising a certain ratio of chemical composition for the preparation of granules, followed by drying and calcining for their crystallization, wherein a step of recycling some final products to the crystallization device has contributed much to settlement of several problems associated with the continual operation, since the recycling process makes it possible to separate the reactants, which may be sintered in the device at a high temperature (500-800° C.), from inner wall of the crystallization device. According to this invention, the recycling step of final product in small amounts is available in that from the step of preparing granules, the round-form agglomeration may minimize the contact area in the crystallization device.
As described in the respective patents (U.S. Pat. No. 5,567,404, its corresponding Korea Patent No. 139976 and Korea Patent Appln. No. 97-33207) disclosed by the inventor et al, the agglomeration step highlighted by this invention, which has several advantages in that a) unlike the conventional method with crystallization process for powder material, high-density materials supplied to crystallization device may cause no dust with a higher unit productivity; b) minimization of contact area with the device due to agglomeration may significantly prevent any attachment caused by the sintering of reactants. However, the manufacturing method using the agglomeration step has failed to efficiently prevent the attachment of reactants to the inner wall of calcination device during mass production of continual operation.
To efficiently prevent the attachment of granules to the device, a
Jeong Soon Yong
Kim Jong Ah
Lee Jung Min
Park Chun Hee
Park Jeong Hwan
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Korea Research Institute of Chemical Technology
Nguyen N. M.
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