Chemistry of inorganic compounds – Sulfur or compound thereof – Binary compound
Reexamination Certificate
2001-03-22
2003-06-24
Silverman, Stanley S. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Binary compound
Reexamination Certificate
active
06582675
ABSTRACT:
INTRODUCTION AND BACKGROUND
The present invention relates to a method of preparing anhydrous sodium sulfide by drying hydrated sodium sulfide.
One can find a hydrated sodium sulfide with an Na
2
S fraction of, in particular, 60 to 62%, as a product available on the market. According to stoichiometric calculation, this corresponds approximately to Na
2
S.3H
2
O. By introducing hydrogen sulfide into concentrated sodium hydroxide, a sodium sulfide hydrate melt, with a content of about 60% to 62% Na
2
S, is formed at temperatures above 100° C. This is placed on a cooling conveyor, on which it solidifies (T<90° C.). After comminution, one generally obtains a scaly product, which is commonly available on the market.
From the state of the art, methods for the preparation of anhydrous sodium sulfide from Na
2
S.9H
2
O, Na
2
S.6 H
2
O or Na
2
S.5H
2
O are already known. In accordance with EP-B-0345 136, which is incorporated herein by reference, the monohydrate is prepared in a first dehydration stage. A time of 2 hours or more is necessary for the removal of water. The remaining water contained in the monohydrate is then removed at a temperature of 90 to 200° C. and a reduced pressure of approximately 2.66 kPa (20 torr) to 66.5 kPa (500 torr). A similar two-stage method for the preparation of crystalline, anhydrous sodium sulfide is described in EP-B 0361 998, which is also incorporated by reference herein.
In the method described in EP 0924165, which is incorporated herein by reference, hydrated sodium sulfide, having a water content of 35 to 45 wt %, is heated under reduced pressure for the preparation of anhydrous sodium sulfide. The sodium sulfide is conveyed while it is being mixed by a device, the temperature of the supplied Na
2
S hydrate steadily rising from approximately 20° C., at the point where the solid is fed, to ≧180° C. at the exit for the solid. A reduced pressure of <20 torr is simultaneously maintained.
Disadvantages of these known methods include the fact that one must wait for the complete reaction, for example, to the monohydrate, in the first stage (EP-B-0345 136), before this compound can be supplied to the second temperature stage, or that the vaporization rate is very high (EP 0924165).
SUMMARY OF THE INVENTION
The object of the invention is therefore to provide a method by which an essentially anhydrous sodium sulfide is obtained, while avoiding the disadvantages inherent in existing processes.
This and other objects of the invention are obtained by a method for the preparation of anhydrous sodium sulfide with a content of at least 98 wt % Na
2
S, preferably at least 99 wt. % Na
2
S, by drying hydrous sodium sulfide, with a water content of 35 to 45%, wherein the hydrous sodium sulfide is used as a solid or in the liquified form, and is dried at a high temperature while it is being mixed and conveyed.
REFERENCES:
patent: 4784805 (1988-11-01), Blattner
patent: 0 345 136 (1994-03-01), None
patent: 0 924 165 (1999-06-01), None
patent: 4-310508 (1992-11-01), None
1 Page Description of “Discotherm B Processor” Bearing a Docld=54E56C82-ED Sep. 23, 2002 and a Copyright Date of 1996-2002 Obtained from http://www.chemicalonline.com and 1 Page Titled “Available Equipment for Test or rental” Obtained From http://www.listgrp.com.
Degussa - AG
Silverman Stanley S.
Smith , Gambrell & Russell, LLP
Vanoy Timothy C
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