Process for preparing silanes

Details Process for preparing silanes Process for preparing silanes

2002-05-03

2003-04-01

Shaver, Paul F. (Department: 1621)

Organic compounds -- part of the class 532-570 series

Organic compounds

Silicon containing

C423S344000

Reexamination Certificate

active

06541650

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for preparing silanes from hydrogen chloride gas and silicon metal, disilanes, and oligosilanes as reactants.
2. Background Art
In the preparation of chlorosilanes, silicon is reacted with hydrogen chloride gas, if appropriate in the presence of catalysts, resulting, depending on the reaction conditions, in the formation of trichlorosilane or tetrachlorosilane as the main product. The reaction temperature selected depends greatly on the desired target product (HSiCl
3
or SiCl
4
) and is normally from 230° C. to several hundred ° C. Trichlorosilane is used, for example, for the preparation of high-purity silicon or the preparation of (organo)functional silanes, while tetrachlorosilane is used, for example, in the preparation of pyrogenic silica. The relevant technology is described in
Catalyzed Direct Reactions of Silicon
, edited by K. L. Lewis and D. G. Rethwisch, Ed.s Elsevier 1993; “Commercial Production of Silanes by Direct Synthesis,” pages 1-66 and “Direct Synthesis of Chlorosilanes and Silane,” pages 441-457.
In the direct synthesis of methylchlorosilanes by the Muller-Rochow method (direct synthesis), silicon is reacted with methyl chloride in the presence of catalysts and promoters to form dimethyldichlorosilane, with higher-boiling methylchlorodisilanes and methylchlorooligosilanes and the corresponding siloxanes and carbosilanes also being formed as by-products. Lewis,
op. cit
., pp. 1-66. U.S. Pat. No. 5,877,337 describes a process in which solids-containing residues from the direct synthesis of organochlorosilanes are worked up at low pressures and the organosilicon components are converted into useful silanes. This objective is achieved by carrying out thermal cracking of the residues from the direct synthesis in the presence of hydrogen chloride in a tube reactor containing rotating internals at temperatures of 300-800° C. The rotary motion of the internals shears off deposits on the reactor walls caused by carbon formation or solid components. This is said to prevent blocking of the reactor.
In these processes, hydrogen chloride gas is required and the reactions are carried out at relatively high temperatures. The hydrogen chloride gas is taken from appropriate storage tanks and may have to be preheated. In Lewis,
op. cit
., for example, it is stated on page 6 that liquid anhydrous hydrogen chloride which is used in the direct synthesis of chlorosilanes is typically transported to production sites in cooled tank cars. HCl is vaporized, heated to about 200° C. and subsequently introduced into the reactor.
The preparation of HCl from the elements is known. H
2
and Cl
2
are introduced separately into a combustion chamber, mixed and reacted in a burner flame. The reaction is strongly exothermic, so that flame temperatures of above 2000° C. are possible. The hydrogen chloride gas is subsequently cooled by means of appropriate cooling apparatuses.
SUMMARY OF THE INVENTION
The present invention avoids all or a portion of the energy penalty required to heat hydrogen chloride gas prior to the commercial preparation of silanes by the in situ generation of hydrogen chloride by combustion of hydrogen and chlorine. Numerous advantages other than thermal efficiency surprisingly accrue from this process.


REFERENCES:
patent: 5288892 (1994-02-01), Pachaly et al.
patent: 5292909 (1994-03-01), Chadwick et al.
patent: 5877337 (1999-03-01), Mautner et al.
patent: 0 634 417 (1995-01-01), None
patent: 0 869 129 (1998-10-01), None
Caplus-Abstract Corresponding To JP-A 11092130 [AN 1999:225513].
Caplus-Abstract Corresponding To BR-A 8 006 892 [AN 1983:200732].
Derwent Abstract Corresponding To EP-A 634417 [AN 1998-507568].
Caplus-Abstract Corresponding To JP-A 07206421 [AN 1995:922114].
Caplus-Abstract Corresponding To BR-A 9 002 380 [AN 1993:41833].
K.L. Lewis/D.G. Rethwisch, “Catalyzed Direct Reactions of Silicon”, Elsevier 1993, pp. 1-66 and 441-457.

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