Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Reexamination Certificate
2001-03-21
2001-11-27
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
Reexamination Certificate
active
06323357
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for the direct synthesis of organochlorosilanes using CuCl prepared from the copper-containing residues from the direct synthesis of organochlorosilanes.
2. Background Art
In the so-called “direct synthesis” of organochlorosilanes, in particular methylchlorosilanies, metallic silicon is reacted with chloromethane in the presence of copper catalysts, optionally in the presence of further cocatalysts and promoters. When the direct synthesis is performed industrially in fluidized-bed reactors, fine fractions of silicon and copper catalyst, contaminated by carbon particles and by various metal compounds from the secondary constituents derived from the technical-grade silicon raw material, are discharged together with the crude silane reaction product and unreacted chloromethane, and separated therefrom by downstream separation units, for example, cyclones. Furthermore, a reactor residue comprising silicon, catalyst, and metal halides is formed, and is discharged continuously or batchwise from the fluidized-bed reactors. Drying and filtration processes also result in the formation of contaminated fine dusts.
Processes for the recovery of the copper from reactor residue and fine dusts are known. For example, U.S. Pat. No. 5,306,328 discloses that the copper content of residues from the synthesis of methylchlorosilane can be converted into soluble copper(II) salts. These copper(II) salts can be reduced to copper metal using iron powder. The disadvantage of this process is that iron and copper must be employed at least in a molar ratio of 1:1, and that if copper is not employed as a catalyst in metallic form, further processing is necessary.
Processes for the preparation of CuCl from aqueous solutions are known. In these processes, pure Cu(II) compounds or so-called “metallic waste copper” are preferably used as sources of copper, and dissolved in mineral acids such as hydrochloric acid. Hydrochloric acid-containing CuCl
2
solutions formed in etching processes for the production of circuit boards are also used. Solutions of this type, compared with the solutions produced in aqueous work-up of the process residues from the direct synthesis, have a relatively low content of additional impurities, for example, metal chlorides. After filtration, the copper-containing solutions are reduced to Cu(I) compounds with the aid of a suitable reducing agent, such as, for example, Cu, Fe, Zn, Al, hydroxylamine, sulfurous acid or SO
2
. During this process, it is ensured that the CuCl formed remains in dissolved form through addition of complexing agents such as NaCl and/or hydrochloric acid. After re-filtration, the solubility is then reduced to below the limit for CuCl by suitable measures, so that the solid CuCl at least partially precipitates. This can be achieved, for example, by diluting the solution massively with water. The solid CuCl is separated by filtration, washed, and dried. This process is described, for example, in Ullmann's Encyclopedia of Industrial Chemistry, Volume A7, page 574.
The disadvantages of the foregoing process are that, first, due to the heavy dilution, relatively large reaction volumes and amounts of water are necessary, second, the resulting filtrates have to be worked up or suitably disposed; third, that an additional filtration step is necessary; and finally, relatively pure Cu(II) solutions are required as starting materials.
DE 901889 discloses that copper(I) chloride can be prepared in a yield of 85-90% from a copper(II) chloride solution with the aid of a reducing agent such as sulfur dioxide, sodium bisulfite or sodium sulfite. U.S. Pat. No. 4,758,352 discloses that the copper(I) chloride in the process described in DE 901889 is not separated quantitatively. The reason for the non-quantitative separation is given in Ullmann's Encyclopedia of Industrial Chemistry, 5th Edition, Volume A7, page 574, in which it is shown that with increasing chloride ion concentration in the solution, the solubility of CuCl likewise increases considerably.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a process by means of which CuCl useful as an effective catalyst in the direct synthesis of organochlorosilanes can be prepared in a simple manner and in high yields from the copper-containing residues from the direct synthesis of organochlorosilanes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The present invention pertains to a process for the direct synthesis of organochlorosilanes using a CuCl catalyst component prepared from the copper-containing residues from the direct synthesis of organochlorosilanes, where, in the preparation of the CuCl catalyst, in a first step, copper from an aqueous suspension of the copper-containing residues from a direct process organochlorosilane synthesis is oxidized to CuCl
2
using mineral acid and oxidant, where the mineral acid, the oxidant or both the mineral acid and the oxidant contain chlorine, thereby providing an aqueous CuCl
2
solution, and in a second step, this aqueous CuCl
2
solution is reduced to CuCl using elemental iron.
The process is distinguished by the fact that CuCl can surprisingly be prepared in high yield and adequate purity from relatively highly contaminated CuCl
2
solutions without the disadvantages disclosed by the prior art arising. The recovered CuCl can be employed as an effective catalyst in the direct synthesis of organochlorosilanes. Compared with Cu oxide-based catalysts and copper metal catalysts, use of CuCl catalysts in the direct synthesis has the advantage that the reaction is initiated more quickly, that a smaller amount of catalyst is required for comparable reactivity, and that the reactivity of the catalyst is higher than a comparable amount of copper oxide-derived or metallic copper-containing catalyst based on metallic copper.
The isolation of the copper salt solution in the first step from process residues from the synthesis of organochlorosilanes, in particular methylchlorosilane, is described, for example, in U.S. Pat. No. 5,306,328, incorporated herein by reference. The process residues are, in particular, solid residues which preferably contain less than 1% by weight of silanes.
In a first step, the process residues are preferably suspended in acidic washing solutions produced in the work-up process. A mineral acid, preferably hydrochloric acid or sulfuric acid, is then added, and the suspension is treated with an oxidant, preferably oxygen, chlorine, NaOCl or H
2
O
2
. At least one of the two components comprising the mineral acid and the oxidant must contain chlorine or chloride. During this operation, all metal salts which usually occur in process residues in the synthesis of methylchlorosilane and some of the metals contained therein go into solution, while silicon and both the majority of the silicides, for example, iron disilicide, and carbon, remain undissolved. Particular preference is given to the recovery of copper(II) chloride using hydrochloric acid and oxygen. The oxygen can be supplied as atmospheric oxygen, as the pure gas, as oxygen enriched air, or as oxygen admixed with any non-interfering gas, i.e. nitrogen.
In order to separate accompanying insoluble substances such as fine carbon particles and silicon particles, the copper-salt solution is preferably filtered before further processing. It is possible to add auxiliaries such as flocculants, antifoams and filter aids to the copper-salt solution. After washing, the filter cake is substantially free from elutable toxic metal compounds and can either be sent to a sanitary landfill or employed as a raw material or aggregate in other processes, for example, as an aggregate for mineral building materials. The wash solutions can be re-employed for suspending the process residues.
In a second step, the aqueous CuCl
2
solution is reacted with elemental iron, preferably with agitation. Iron powder having a mean particle size in the range of 0.1 to 300 &mgr;m is preferred, since the high surface area
Goetze Ulrich
Kalchauer Wilfried
Straussberger Herbert
Streckel Willibald
Brooks & Kushman P.C.
Shaver Paul F.
Wacker-Chemie GmbH
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