Chemistry of inorganic compounds – Silicon or compound thereof – Oxygen containing
Patent
1992-05-26
1993-06-01
Chaudhuri, Olik
Chemistry of inorganic compounds
Silicon or compound thereof
Oxygen containing
252135, C01B 3332
Patent
active
052157326
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1.
The invention relates to a process for the production of alkali metal silicates from crystalline SiO.sub.2 -containing material and aqueous alkali metal hydroxide solution at elevated temperature and under normal pressure.
2. Statement of Related Art
Alkali metal silicates, e.g. water glasses, are produced in large quantities and are used both in solution and also as solids in many fields. Among such are washing and cleaning agents, adhesives, paints, the floatation of ore, and water treatment. They also serve as raw materials for the production of zeolites as well as silicic acids, silica sols, and silica gels (Buchner et. al., Industrielle Anorganishce Chemie (Industrial Inorganic Chemistry), Verlag Chemie, 1984 p. 333).
Waterglass solutions are usually characterized by two physical values. Firstly, by the molar ratio SiO.sub.2 /M.sub.2 O, hereafter referred to as the modulus, and by the solids content, i.e. the proportion by weight of SiO.sub.2 and M.sub.2 O in the solution, where M stands for Na or K. Both factors influence the viscosity of the alkali metal silicate solution.
The maximum solubility of an alkali metal silicate with a specific modulus can be determined from tables and diagrams. Generally, at higher alkali contents, i.e. a lower modulus, higher solids contents can be achieved in the solution. Waterglasses up to a modulus of 4.3 are obtained via melting processes. Such melting processes have already been known since the last century; the only process still used nowadays is the conversion of quartz sand with soda at temperatures around 1500.degree. C. (Winnacker-Kuchler, Chemische Technologie (Chemical Technology), C. Hanser Verlag, 4th Edition (1983), Volume 3, Anorganishce Technologie II (Inorganic Technology II), page 58 et seq.). Only a small proportion of the alkali metal silicate prepared in this way is sold as solid glass. Most of it is subsequently dissolved in water. For glasses with a modulus >2.0 the reaction velocity at the reflux temperature of the solution is not satisfactory, so that a pressurized decomposition at 4-6 bar and 150.degree. C. is preferred.
Low molecular ratio waterglasses (modulus <2.7) which are richer in alkali can also be prepared hydrothermally e from quartz sand and concentrated aqueous sodium hydroxide solution. For that purpose, because of the low reactivity of quartz sand, raised temperatures and increased pressure are necessary. In industry two processes are used: nickelplated rotating pressure dissolvers at temperatures of 200 to 220 .degree. C. and tubular reactors at temperatures of 250.degree. to 260 .degree. C. (Winnacker-Kuchler, loc. cit., page 61 et seq.).
Finely divided, amorphous silicic acids dissolve ex othermically in alkali lyes. Thus, occasionally particularly pure alkali metal silicate solutions are obtained by the reaction of pyrogenic or precipitated silicic acid with an alkali lye. Apart from special cases, this process is & too costly.
Amorphous silicic acid also occurs as by-product or waste in various industrial processes. Numerous processes for employing such silicic acids are documented.
According to Przem. Chem. 67(8) (1988) 384-6 (Chemical Abstracts 109:214144f), sodium silicate solutions with a middling modulus can be obtained from the waste silicic acid from the preparation of AlF.sub.3 and HF.
According to JP-76 17519 (Chemical Abstracts, 86:19 116 g) dust from the preparation of ferrosilicon contains about 90 wt-% of highly-reactive SiO.sub.2, which can be converted with 8.1% sodium hydroxide solution at temperatures around 90.degree. C. to a waterglass solution with a high modulus.
As another alkali metal silicate, solid crystalline anhydrous sodium polysilicate (Na.sub.s SiO.sub.2).sub.00 has industrial importance as builder component in washing and cleaning agents. This sodium silicate with the empirical composition Na.sub.2 SiO.sub.3 contains endless chains of SiO.sub.4 tetrahedrons, which are bonded to the sodium atoms via bridges. Such chain silicates are called "inosilicates" in
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patent: 5000933 (1991-03-01), Novotny et al.
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Christophliemk Peter
Dolhaine Hans
Foell Juergen
Hachgenei Johannes W.
Novotny Rudolf
Chaudhuri Olik
Henkel Kommanditgesellschaft auf Aktien
Horton Ken
Jaeschke Wayne C.
Szoke Ernest G.
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