Patent Application
20100168458
The invention relates to a process for converting Si—H compounds into Si-halogen compounds in the gas phase by means of hydrogen halide.
In the preparation of halosilanes or organohalosilanes, mixtures which also contain Si—H-containing silanes are frequently obtained. The silanes can be desirable and can be isolated in pure form from the mixtures. However, they can also be undesirable and therefore have to be removed. The most common method of fractionating silane mixtures is distillation. If the boiling points of Si—H-containing silanes and one or more other silanes are quite close together or an azeotrope is formed, the distillation becomes complicated and costly.
U.S. Pat. No. 5,336,799 A describes the conversion of Si—H-containing compounds into the corresponding organosilanes by reaction with organic halides over Pt or Pd catalysts. The reaction rates are slow and comparatively expensive organic halides are required.
EP 423948 A describes the reaction of Si—H-containing organosilanes with hydrogen halide over metal catalysts such as Pd, Pt, Ni to form organohalosilanes. The catalysts are expensive and deactivation of the catalysts by slow oxidation to metal halides takes place.
U.S. Pat. No. 5,302,736 A describes Ag or Au catalysts for this purpose, but the reaction proceeds too slowly.
U.S. Pat. No. 3,754,077 A describes the conversion of halosilanes having one or more Si—H bonds into tetrahalosilane in the gas phase by means of hydrogen halide over solid catalysts such as activated carbon, Al2O3 or SiO2. The process has been developed only for silanes without an organic radical and requires temperatures at or above 200° C.
It is an object of the invention to provide an improved process for converting the Si—H-containing silanes into silanes having altered boiling points.
The invention provides a process for converting silicon compounds (H) which have Si—H bonds into silicon compounds (Cl) which have Si-halogen bonds, wherein the silicon compounds (H) are reacted in the gas phase with hydrogen halide in the presence of catalysts selected from among
(a) tetraorganophosphonium halides,
(b) tetraorganoammonium halides and
(c) ionic halides of heterocycles which are organically substituted on the heteroatom.
The process proceeds at relatively low temperatures and is suitable for all vaporizable silicon compounds (H) which have Si—H bonds. The catalyst has very long operating lives and is very easy to handle.
Preferred silicon compounds (H) which have Si—H bonds are organopolysiloxanes, organopolysilanes and in particular monosilanes.
The silanes (H) preferably have the general formula 1
RxSiH4-x (1),
where
R is a monovalent, C1-C18-hydrocarbon radical which may be substituted by halogen radicals or is a halogen radical and
x is 1, 2 or 3.
The C1-C18-hydrocarbon radicals R are preferably phenyl radicals or C1-C6-alkyl radicals, a vinyl or allyl radical, in particular methyl or ethyl radicals. Halogen substituents on R are preferably fluorine, chlorine and bromine, in particular chlorine.
Halogen radicals R are preferably fluorine, chlorine and bromine, in particular chlorine.
The process of the invention is suitable for use in the purification of crude products and prepurified products from the direct synthesis of methylchlorosilanes, in particular of methylchlorosilanes which contain, as by-products, silicon compounds (H), in particular EtHSiCl2, and possibly further by-products. The preferred concentration of silicon compounds (H) in the methylchlorosilanes is from 10 to 5000 ppm.
The hydrogen halide used is preferably hydrogen chloride or hydrogen bromide, in particular hydrogen chloride.
Preference is given to using from 1.5 to 50 mol, in particular from 3 to 10 mol, of hydrogen halide per mole of hydrogen of the silicon compounds (H).
As catalysts (a) and (b), preference is given to using:
(a) tetraorganophosphonium halides of the general formula 2
R14PX1 (2)
and
(b) tetraorganoammonium halides of the general formula 3
R24NX2, (3)
where
R1 and R2 are each an optionally halogen-substituted, optionally heteroatom-containing C1-C18-hydrocarbon radical and
X1 and X2 are each a halogen atom.
R1 and R2 can be, for example, branched, unbranched or cyclic alkyl radicals and multiple bond systems such as aryl, alkaryl and aralkyl radicals. The radicals R1 and R2 preferably have from 1 to 10 carbon atoms; in particular, the radical R1 and R2 is an alkyl radical having from 2 to 8 carbon atoms.
The halogen atom X1 or X2 is preferably chlorine, bromine or iodine, in particular chlorine.
Preference is given to (n-butyl)4PCl and (n-butyl)3(n-octyl)PCl. The preparation of such homogeneous catalysts by alkylation of tertiary phosphines by means of alkyl halides is described, for example, in Houben-Weyl, Georg Thieme Verlag, volume XII/1, pp. 79-90, 1963.
As catalysts (c), preference is given to using: halide salts of positively charged heterocycles in which nitrogen or phosphorus atoms are organically substituted.
Preferred positively charged heterocycles are imidazolium salts and pyridinium salts, in particular imidazolium salts of the general formula 4
and
pyridinium salts of the general formula 5
where
R8 is hydrogen or has the meanings of R1 and R2, R7, R9 and R10 have the meanings of re and R2 and X3 and X4 have the meanings of X1 and X2.
The halogen of the hydrogen halide used preferably corresponds to the halogen of X1, X2, X3 and X4. In particular, X1, X2, X3 and X4 are each hydrogen chloride.
In a preferred embodiment, the catalysts (c) are ionic liquids, namely low-melting salts. Their preferred melting points for the present process are not more than 150° C., preferably not more than 100° C. at 1 bar. The radicals of the cations of the ionic liquids preferably correspond to the above-described radicals R1 and R2.
It is possible to use pure catalysts (a), (b) or (c) or a mixture of catalysts selected from among the catalysts (a), (b) and (c).
The hydrogen halide used is preferably hydrogen chloride or hydrogen bromide, in particular hydrogen chloride.
The catalysts (a), (b) and (c) are preferably used in undiluted form or as a solution in a preferably high-boiling inert organic solvent, preferably a hydrocarbon such as tetralin or decalin. The catalysts (a), (b) and (c) can also be used on solid supports.
Pressure and temperature can be varied within wide ranges and are preferably matched to the conditions of an upstream column which provides a fraction enriched in silicon compounds (H), in particular EtHSiCl2.
The process of the invention is preferably carried out at temperatures at which the silicon compounds (Cl) are liquid. The process of the invention is in particular carried out at at least 30° C., in particular at least 70° C., and preferably at temperatures of not more than 160° C., in particular not more than 120° C.
The process of the invention is preferably carried out in a tube reactor, with the mixture preferably being fed in in vapor form.
All symbols in the above formulae have their meanings independently of one another in each case.
In the following example, all amounts and percentages are, unless indicated otherwise, by weight, all pressures are 0.10 MPa (abs.) and all temperatures are 20° C.
A tube reactor which has an internal diameter of 20 mm and a length of 600 mm and is heated by means of a heat-transfer medium is charged with 80 g of tetra-butylphosphonium chloride. 230 g/h of a gaseous methylchlorosilane fraction containing 360 ppm of ethyldichlorosilane and 1300 ppm C7-C8 hydrocarbons are passed together with 1 l/h of hydrogen chloride through the catalyst at a temperature of the heat-transfer medium of 90° C. and a gauge pressure of 10 mbar. The height of the bubble column is established at about 500 mm. The product condensed with slight reflux in a 30 cm long packed column is analyzed by means of GC. It contains 20 ppm of ethyldichlorisilane; the C7-C8 hydrocarbons are not dissociated.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 030 948.3 | Jul 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/057257 | 6/11/2008 | WO | 00 | 1/14/2010 |
