Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2000-10-24
2001-09-11
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06288258
ABSTRACT:
This invention relates to a process for preparing organohalosilanes, and more particularly, to a direct synthesis process for continuously preparing organohalosilanes by effecting gas-solid catalytic reaction between metallic silicon and organohalide in the presence of a copper catalyst.
BACKGROUND OF THE INVENTION
With respect to the synthesis of organohalosilanes, Rochow first disclosed in U.S. Pat. No. 2,380,995 direct synthesis reaction between metallic silicon and organohalide in the presence of a copper catalyst. Since then, there have been reported a number of research works relating to copper catalysts and treatment thereof, co-catalysts used together with copper catalysts, reactors, additives used during reaction, and the like. In the industrial synthesis of organohalosilanes, the selectivity of diorganodihalosilane which is most widely used in silicone resins, the formation rate of silanes, and the percent conversion of metallic silicon into useful silane are crucial. The selectivity of diorganodihalosilane is evaluated in terms of a weight or molar ratio of dialkyldihalosilane to the silanes produced and a T/D ratio. Organohalosilane products contain diorganodihalosilane (D), triorganohalosilane (M), organotrihalosilane (T), etc. as well as other by-products such as organohydrodihalosilane (H) and organohalodisilanes. Particularly when silicones are manufactured using the direct method organohalosilane product as a starting material, few processes are available for the effective utilization of disilanes known as a high-boiling fraction. Thus, most disilanes are discarded as the residue.
The T/D ratio is a compositional ratio of organotrihalosilane to diorganodihalosilane in the entire organohalosilanes produced, with a lower T/D ratio being preferred. The formation rate of organohalosilane is represented by a space time yield (STY) which is the weight of crude organohalosilane produced per unit time relative to the weight of metallic silicon held in the reactor. In order to improve the content of diorganodihalosilane produced, reduce the T/D ratio or increase the STY, various research works have been made with a focus on the catalyst and promoter.
U.S.S.R. Application Specification No. 1,152,943 (Certificate of inventorship No. 237,892) dated Nov. 20, 1969 discloses to add a phosphorus-copper-silicon alloy to a contact mass so as to give 2,500 to 30,000 ppm of phosphorus, thereby improving the dimethyldichlorosilane content to 82.3%. Use of a promoter-containing metallic silicon alloy is not adequate to industrial scale reaction, and the STY and silane composition are unsatisfactory. U.S. Pat. No. 4,602,101 corresponding to JP-B 5-51596 discloses that 25 to 2,500 ppm of a phosphorus compound capable of generating elemental phosphorus in the reactor is added to a contact mass. Although the results of reaction according to this U.S. patent are improved over the U.S.S.R. patent, there still remain many problems including hazard imposed by spontaneously igniting elemental phosphorus and increased cost of raw materials. Then this U.S. patent is also unsuitable to apply to commercial scale reactors. There is no teaching about the effect available with a phosphorus concentration of at least 2,500 ppm. Also, F. Komitsky et al., Silicon For the Chemical Industry IV, Geiranger, Norway (1998), page 217, proposes the addition of phosphorus in the form of copper phosphide, leaving problems including a low percent conversion, ineffective utilization of phosphorus, and difficult control of a phosphorus concentration.
JP-A 11-228580 or EP 893408 (Pecine Electrometallurgy) discloses that active silicon powder is prepared by milling metallic silicon in a rod mill or ball mill using rods or balls of bronze phosphide whereby bronze phosphide finely adheres to surfaces of silicon particles, rendering the silicon particles active. The bronze phosphide used therein is ordinary bronze phosphide having a phosphorus concentration of up to 1% by weight. Phosphorus is added in the form of iron phosphide. This gives rise to essentially the same problem as the prior art proposals.
SUMMARY OF THE INVENTION
An object of the invention is to provide a direct synthesis process for preparing organohalosilanes in a low T/D ratio and a desired STY while restraining the formation of disilanes.
It is desirable to have a process for preparing organohalosilanes by the industrially advantageous direct method, and especially a direct synthesis process for preparing organohalosilanes in the desired STY while increasing the content of diorganodihalosilane and restraining the formation of unnecessary disilanes. We have found that when a specific amount of bronze phosphide is added to the reaction contact mass containing metallic silicon, phosphorus and tin in the bronze phosphide cooperate so as to restrain the formation of disilanes while maintaining reaction activity, whereby the content of diorganodihalosilane is enhanced.
The invention provides a process for preparing oganohalosilanes comprising the steps of charging a reactor with a contact mass containing metallic silicon and a copper catalyst, and introducing an organohalide-containing gas into the reactor to effect reaction to form organohalosilanes of the following general formula (1):
R
n
H
m
SiX
(4−n−m)
(1)
wherein R is a monovalent hydrocarbon group, X is a halogen atom, n and m each are an integer of 0 to 4, wherein 50 to 10,000 ppm of bronze phosphide is added to the contact mass.
REFERENCES:
patent: 4602101 (1986-07-01), Halm et al.
patent: 5973177 (1999-10-01), Kuivila et al.
patent: 6057469 (2000-05-01), Margaria et al.
patent: 6090966 (2000-07-01), Nakanishi et al.
patent: 6175030 (2001-01-01), Kalchauer et al.
patent: 237892 (1969-11-01), None
Komitsky, Frank, Jr., et al., “The Influence of Promoter Levels on the Direct Synthesis,”Silicon for the Chemical Industry IV, Geiranger, Norway, pp. 217-225 (1998).
Aramata Mikio
Fujimoto Tatsuya
Inukai Tetsuya
Ishizaka Hajime
Saito Ryuichi
Millen White Zelano & Branigan P.C.
Shaver Paul F.
Shin-Etsu Chemical Co. , Ltd.
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