Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2002-02-14
2003-01-14
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C536S063000
Reexamination Certificate
active
06506923
ABSTRACT:
This invention relates to an industrial process for preparing organohalosilanes.
BACKGROUND OF THE INVENTION
With respect to the synthesis of alkylhalosilanes, Rochow first disclosed in U.S. Pat. No. 2,380,995 direct synthesis reaction between metallic silicon and alkyl halide in the presence of a copper catalyst. Since then, there have been reported a number of research works relating to various 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 organohalodisilane. In particular, disilanes are known as a high-boiling fraction among silicone manufacturers because few processes are available for the effective utilization of disilanes, and most disilanes are discarded. 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 diorganohalosilane produced, reduce the T/D ratio or increase the STY, various research works have been made with a focus on the catalyst and co-catalyst.
USSR Application Specification No. 617,569 (Certificate of inventorship No. 122,749) dated Jan. 24, 1959 discloses reaction in the presence of metallic silicon-copper alloy with 20 to 40 ppm of antimony added. Allegedly, the dimethyldichlorosilane content is improved from 40% to 60%. U.S. Pat. No. 4,500,724 discloses use of a copper/zinc/tin catalyst containing 200 to 3,000 ppm of tin, thereby achieving an improvement of T/D to 0.037. Japanese Patent Publication (JP-B) No. 6-92421 discloses reaction using copper arsenide having an arsenic concentration of at least 50 ppm. It is described in these patent references that reactivity, more specifically the rate of reaction of metallic silicon is improved by adding these tin, antimony and arsenic co-catalysts to a reaction contact mass comprising metallic silicon and copper.
USSR Application Specification No. 903,369 (Certificate of inventorship No. 178,817) dated Jun. 2, 1964 discloses that a co-catalyst selected from the group consisting of zinc, bismuth, phosphorus (200 ppm), arsenic, tin, and iron improves the dimethyldichlorosilane content to 72.1% from the value achieved by the above-referred Application Specification No. 617,569 (Certificate of inventorship No. 122,749). Also USSR 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%. Moreover, 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 last-mentioned USSR patent, there still remain many problems including hazard imposed by spontaneously igniting elemental phosphorus and increased cost of raw materials. Then this US patent is also unsuitable to apply to commercial scale reactors. 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. U.S. Pat. No. 6,025,513 discloses to add boron to a contact mass wherein the boron concentration is controlled so as to improve productivity. U.S. Pat. No. 5,059,706 discloses to introduce a phosphorus compound in a vapor phase into a reactor for increasing selectivity. U.S. Pat. No. 6,005,130 discloses to introduce organomonophosphine for increasing selectivity.
However, the phosphorus base additives used in the prior art have an outstanding trade-off between activity and composition selectivity. In particular, it is pointed out that oxide originating from phosphorus can exacerbate flow on the particle surface. Therefore, the conventional phosphorus base additives offer few merits on the continuous operation of commercial scale reactors. Other additives are known from L. Rosch, W. Kalchauer et al., Silicon for the Chemical Industry IV, Sandefjord, Norway (1996) wherein monomethyldichlorosilane is introduced for improving activity. This additive is effective only at the initial period, but not regarded as exerting a lasting effect during the continuous operation of commercial scale reactors.
As seen from the above discussion, engineers involved in most of the above-referred proposals were interested in elements of which the catalyst is made. A more recent approach for improving catalysis was made from a new standpoint. For example, JP-A 2000-254506 discloses an industrial organohalosilane production process using a thermally active metallic copper powder having substantial strain energy. JP-A 2000-296334 discloses an industrial organohalosilane production process using a copper powder in the form of flakes or scales.
However, the organohalosilane synthesis reaction in these processes is heterogeneous gas-solid reaction in a fluidized bed, agitated fluidized bed or fixed bed. The results of reaction largely depend on the powder behavior of the contact mass or catalyst. In particular, since the copper catalyst and co-catalyst are used in excess in the industry, the powder in the contact mass can agglomerate, interfering with the flow of the contact mass and detracting from productivity.
SUMMARY OF THE INVENTION
An object of the invention is to provide a novel and improved process for preparing organohalosilanes at a drastically increased formation rate without lowering the selectivity of useful silane.
Intending to solve the actual drawback encountered in the practice of the prior art direct method or Rochow method, that is, the drawback that the copper catalyst and co-catalyst used in excess causes the powder in the contact mass to agglomerate to interfere with the flow of the contact mass and detract from productivity, we have made efforts to establish a catalyst system capable of satisfying both the chemical action of the catalyst and the flow of the catalyst powder and the contact mass containing the same. We have discovered that the preparation of organohalosilanes is improved by adding to the contact mass an effective amount of a catalytic metal powder which has been produced by an atomizing technique.
More specifically, we have found that the formation rate of useful silane is drastically increased by adding an atomized catalytic metal powder to the contact mass rather than a resinous powder by an electrolytic method, an angular or flaky powder by stamping and grinding methods, a powder by heat treatment, and a flaky or microcrystalline powder from a chemically reduced powder.
We learned that in designing the function of a catalyst in the direct method, the powder performance of a catalyst powder and a contact mass containing the same is largely dependent on how to prepare the catalyst powder. It has been found that an atomized catalyst powder contains more spherical particles and is advantageously applicable to the direct method. The invention uses an atomized catalytic metal p
Aramata Mikio
Inukai Tetsuya
Ishizaka Hajime
Shinohara Toshio
Tanifuji Yoichi
Shaver Paul F.
Shin-Etsu Chemical Co. , Ltd.
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