Organic compounds -- part of the class 532-570 series – Organic compounds – Silicon containing
Utility Patent
2000-01-18
2001-01-02
Shaver, Paul F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Silicon containing
C556S472000
Utility Patent
active
06169195
ABSTRACT:
TECHNICAL FIELD
The invention relates to a process for purifying organochlorosilanes by cleavage of chlorohydrocarbons which are present as an impurity in the commercial production of crude organochlorosilanes.
BACKGROUND ART
Chlorohydrocarbons are formed as secondary constituents of M{umlaut over (u)}ller-Rochow organochlorosilanes synthesis. During separation of the organochlorosilanes by distillation, the chlorohydrocarbons will appear in the various silane fractions according to their boiling range. Chlorohydrocarbons lead to a number of disadvantages, in particular during and after processing of organochlorosilanes to secondary products.
Processes have therefore been developed which separate chlorohydrocarbons from organochlorosilanes. U.S. Pat. No. 4,127,598 describes a process in which chlorohydrocarbons are adsorbed onto active charcoal or molecular sieves. The reduction of chlorohydrocarbons to the corresponding alkanes with hydrogencontaining silanes on aluminum oxide is described in U.S. Pat. No. 4,774,347, and reduction on aluminum oxide-zirconium oxide co-gels is described in U.S. Pat. No. 5,777,145. The preserve of the alkanes thus formed cause no trouble because of their low reactivity. Moreover, the alkanes can usually be separated easily by distillation because of the changed boiling point.
DISCLOSURE OF INVENTION
The invention relates to a process for cleavage of chlorohydrocarbons which are present as an impurity in organochlorosilanes, in which the chlorohydrocarbons are brought into contact with steel surfaces which comprise nickel as an alloying constituent and are cleaved thereby into olefins and hydrogen chloride.
BEST MODE FOR CARRYING OUT THE INVENTION
The organochlorosilanes have the general formula 1
Ra
a
SiCl
4−a
, (1)
in which:
R are identical or different substituents which are chosen from hydrogen, linear or branched alkyl radicals having 1 to 6 carbon atoms or aryl radicals having 6 to 9 carbon atoms and
a is 0, 1, 2, 3 or 4.
In the preferred organochlorosilanes of the general formula 1, R is a methyl or phenyl radical.
During the preparation of organochlorosilanes, by-products which are formed are, inter alia, chlorohydrocarbons which, in particular, have the general formula R′-Cl, in which R′ is an alkyl radical or alkaryl radical having 3 to 20 carbon atoms. The preferred radicals R′ are linear or branched alkyl radicals having 4 to 7 carbon atoms, for example iso-butyl, iso-pentyl, iso-hexyl, 2,3-dimethylbut-2-yl, 3-methylpent-2-yl and 2,3,3-trimethylbut-2-yl. The content of chlorohydrocarbons in the organochlorosilane mixtures is usually 1 ppm to 5000 ppm.
The chlorohydrocarbons eliminate hydrogen chloride on steel surfaces formulated to have a catalytic action, and are converted into olefins. Preferably, in a first embodiment, the steels comprise at least 4% by weight of nickel, in particular 5-70% by weight, a chromium content of at least 10% by weight, in particular at least 16% by weight, and 0 to 20% by weight of molybdenum, preferably 2 to 7% by weight or 13-16% by weight. In a second embodiment, the steels have a nickel content of at least 50% by weight, in particular at least 65% by weight, and a molybdenum content of at least 20% by weight, in particular 25 to 35% by weight. Steels which comprise a chromium content of at least 10% by weight, in particular at least 16% by weight, and at least 5% by weight, in particular at least 5 to 31% by weight of nickel are preferred.
High-grade steel s are preferred. High-grade steels which can be employed are chromium-, nickel- and optionally molybdenum-containing steels (chro-steels), for example standard austenitic steels with 18% of Cr and 10% of Ni or 17% of Cr, 12% of Ni and 2% of Mo, duplex steels with 22% of Cr, 5% of Ni and 3% of Mo or 25% of Cr, 7% of Ni and 4% of Mo, and special austenitic steels with 20-33% of Cr, 18-31% of Ni and 2-7% of Mo, such as are described, for example, in Heinke, G.; Korkhaus, J.; Chemie Ingenieur Technik 69, 283-290. However, high-grade steels of the Ni-Cr-Mo alloy such as are described in Agarwal, D. C.; Herda, W. R.; Materials and Corrosion, 48, 542-548 (1997) can also be employed.
In addition to iron and the alloying constituents mentioned, further elements can also be alloyed in; for example, but not by way of limitation, titanium, copper and niobium. Austenitic steels and duplex steels are preferred.
Examples of the high-grade steels mentioned are materials with the material number 1.4571, 1.4404 and SS316 (17% of Cr, 12% of Ni, in each case 2% of a different alloy) or Hastelloy B2 (72% of Ni, 28% of Cr).
The cleavage of the chlorohydrocarbons increases with an increasing rate as the temperature increases. Cleavage is preferably carried out at 0° C. to 150° C., in particular 70 to 110° C. The residence time can be 1 minute to 10 hours, and is preferably 1 to 5 hours. The pressure is preferably 1 to 2 bar, but lower or higher pressures are also possible.
The steel surfaces can be made available in a suitable geometry, for example in gauzes and in separate reactors. However, they can also be steel baffles of sufficient surface area in apparatuses, such as, for example, distillation columns
The cleavage efficiencies for the chlorohydrocarbons are typically above 90%. The olefins formed can be removed by distillation, since the boiling points of the olefins and of the corresponding chlorohydrocarbons and therefore also of the chlorosilane or chlorosilane mixture in which the chlorohydrocarbon was concentrated on the basis of its boiling point are sufficiently far apart.
REFERENCES:
patent: 4127598 (1978-11-01), McEntee
patent: 4661612 (1987-04-01), George et al.
patent: 4774347 (1988-09-01), Marko et al.
patent: 4962221 (1990-10-01), Huntress et al.
patent: 5777145 (1998-07-01), Marko
International Search Report—Apr. 19, 2000.
“Chemie Ingenieur Technik 69”, pp. 283-290, Mar. 1997.
“Materials and Corrosion” (Jun. 1997), pp. 542-548.
Mautner Konrad
Schinabeck Anton
Brooks & Kushman P.C.
Shaver Paul F.
Wacker-Chemie GmbH
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