Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Patent
1993-06-01
1995-05-23
McFarlane, Anthony
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
423332, 423333, 23302T, C01B 3332
Patent
active
054179513
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a process for the hydrothermal production of crystalline sodium disilicate from quartz sand and sodium hydroxide and/or from aqueous solutions of amorphous sodium disilicate.
STATEMENT OF RELATED ART
Crystalline sodium salts of silicas with an SiO.sub.2 to Na.sub.2 O ratio of 2:1 to 3:1 are normally produced by tempering sodium silicate glasses or by heating sodium carbonate and quartz (DE-OS 31 00 942).
Willgallis and Range (Gastechnische Berichte [Title in English: Glass Technology Reports] 37 (1964), 194-200) describe the production of .alpha.,.beta.- and .gamma.-Na.sub.2 Si.sub.2 O.sub.5 by tempering molten and non-molten, water-free soda waterglass. These products have a layer structure. The fact that they are crystalline forms is apparent from the X-ray diffraction spectra. The authors show that various crystal forms are obtained, depending on the temperature.
In Am. Mineral., 62 (1977), 763-771, Benecke and Lagaly describe a process for the production of a hydrated crystalline sodium silicate of kanemite structure (approximately the composition NaHSi.sub.2 O.sub.5). In a first step, SiO.sub.2 is dispersed in methanol and cold sodium hydroxide is added to the resulting dispersion. This process is complicated by the controlled addition of the individual substances and necessitates special safety precautions on account of the use of inflammable methanol.
DE-OS 34 17 649 describes a process in which crystal nuclei are added to hydrated sodium silicate, the reaction mixture is dewatered by heating and the dewatered reaction mixture is kept at a temperature of at least 450.degree. C., but below the melting point, until the crystalline sodium silicate of layer structure has formed.
Amorphous products are obtained in the dewatering (evaporation) of waterglass solutions or solutions of typical sodium silicates (non-layer-structure) with a molar ratio of SiO.sub.2 to Na.sub.2 O of 1.9:1 to 3.5:1. It is only at temperatures above 450.degree. C. that these products crystallize over a period of several hours in the presence of an aqueous phase (DE-OS 34 17 649). This reaction generally takes several hours. At temperatures between 600.degree. and 850.degree. C., reaction times of only a few minutes and, in the case of certain silicates, fractions of a minute are occasionally sufficient.
EP-A 0 320 771) describes a process for the production of X-ray crystalline sodium disilicate (sodium silicate of layer structure) by dissolution of X-ray crystalline layer silicate in water and subsequent concentration by evaporation at elevated temperature. This process actually starts out from crystalline sodium layer silicate and is specifically intended for the production of detergents and cleaning products containing sodium disilicate. This document merely describes a method of processing crystalline sodium disilicate initially obtained by other processes by dissolution in water and subsequent evaporation of water.
It is equally well known to the expert that the dissolution of amorphous sodium disilicate in water and subsequent concentration by evaporation leads in turn to amorphous sodium disilicate.
It has not so far been possible by known methods directly to obtain highly pure crystalline sodium disilicate under hydrothermal conditions on an industrial scale.
J. Franke (Bull. Soc. Chim., 1950 pages 454 et seq.) describes attempts at the hydrothermal production of sodium disilicate. To isolate the reaction product of quartz and sodium hydroxide solution, the author attempted to crystallize the reaction product using expensive apparatus, in some cases by introducing crystallization nuclei. The reaction products obtained were then left to crystallize for several weeks while cooling, mixtures of amorphous and crystalline sodium disilicate often being obtained.
DESCRIPTION OF THE INVENTION
OBJECT OF THE INVENTION
Now, the problem addressed by the present invention was to provide a simple process which would enable crystalline, high-purity sodium disilicate to be produc
REFERENCES:
patent: 2881049 (1959-04-01), Erbe et al.
patent: 4336235 (1982-06-01), Deabriges
patent: 5211930 (1993-05-01), Schimmel et al.
patent: 5236682 (1993-08-01), Schimmel et al.
patent: 5268156 (1993-12-01), Schimmel et al.
Glastechnische Berichte 37 (1964), 194-200.
American Mineralogist, 62 (1977), 763-771.
Henkel Kommanditgesellschaft auf Aktien
Jaeschke Wayne C.
McFarlane Anthony
Ortiz Daniel S.
Wisdom, Jr. Norvell E.
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