Chemistry of inorganic compounds – Silicon or compound thereof – Elemental silicon
Patent
1995-12-15
1998-02-03
Nguyen, Ngoc-Yen
Chemistry of inorganic compounds
Silicon or compound thereof
Elemental silicon
556472, C01B 3302
Patent
active
057141312
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The innovation relates to a particular type of metallurgical silicon having a controlled structure and containing a controlled quantity of phosphorus whose distribution in the various phases which constitute the structure of the metallurgical silicon is itself controlled.
This type is particularly well adapted to the synthesis reaction of alkyl or aryl halogenosilanes.
DESCRIPTION OF RELATED ART
The synthesis of alkyl or aryl halogenosilanes (which will hereinafter be called "silanes") through the reaction of a halogenated hydrocarbon with silicon in the presence of a copper-based catalyst at a temperature of 250.degree. to 350.degree. C. is known from U.S. Pat. No. 2,380,995 granted to Rochow on Aug. 7, 1945.
This reaction, hereinafter referred to as "the Rochow reaction", has undergone considerable industrial development, having been in particular the basis for the entire silicone industry.
This reaction is generally produced with methyl chloride CH.sub.3 Cl and results in a mixture of various methyl chlorosilanes, particularly monomethyltrichlorosilane CH.sub.3 SiCl.sub.3 (which will hereinafter be called T) and dimethldichlorosilane (CH.sub.3).sub.2 SiCl.sub.2 (which will hereinafter be called D). Since the most sought-after product is D, it is very important to be able to control the reaction in such a way as to obtain the maximum proportion of D in the mixture of silanes obtained, a ratio which is called selectivity. It is also very important to be able to produce the maximum quantity of silanes per unit of time, the value of the weight flow of silanes produced being called reactivity.
Since the initial Rochow patent of 1945, a vast amount of work has been devoted to increasing the reactivity and selectivity of the Rochow reaction. Research had been conducted on the technology of the process--which, while originally carried out in a fixed bed, is now almost always done in a fluidized bed--on the physical form of the silicon used (particle size distribution, etc . . .) and particularly on the catalytic systems used, and on the chemical composition of the silicon, this silicon being an industrial product which contains a certain number of impurities.
U.S. Pat. No. 4,602,101 granted to Halm et al on Jul. 22, 1986, provides (columns 1 through 4) a fairly extensive summary of the knowledge of the catalytic systems studied. This summary shows that a certain number of elements or compounds have been described as catalysts of the Rochow reaction, while others have been indicated as cocatalysts or catalyst promoters because their use in conjunction with certain catalysts makes it possible to improve selectivity and/or reactivity.
The original catalyst, copper, is the most often cited and is utilized universally. However, nickel, antimony, manganese, silver, titanium and iron are also cited as catalysts. Copper can be used either in metallic form or in the form of oxides (possibly formed in situ from other derivatives such as copper nitrate), or in the form of halides.
It is possible to add promoters to these catalysts, or to some of them, which can either be elements such as: as: with copper; copper and/or its oxides, and sometimes with iron.
Some of these catalysts and promoters are particularly noteworthy, specifically copper as a catalyst and zinc, tin and phosphorus as promoters.
Since Jan. 15, 1954, the publication date of U.S. Pat. No. 2,666,776 (Nitzsche et al.), the beneficial influence of phosphorus as a cocatalyst or promoter has been recognized: column 1, lines 26-37, indicates that alkyl or aryl halides of silicon, particularly dialkyl or diarylhalogenosilanes, are obtained by using an alloy which contains, in addition to silicon and copper, a metal from the 5th or 8th group of the periodic table, particularly cobalt, nickel, iron or phosphorus, and that an additional increase in effectiveness is obtained if the catalyst is used in connection with an activation agent, for example a copper salt.
The importance of phosphorus was confirmed, first by Rossmy in his German pat
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Degen Bruno
Licht Elke
Margaria Thomas
Schulze, deceased Manfred
Wagner Gebhard
Bayer AG
Nguyen Ngoc-Yen
Pechiney Electrometallurgie
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