Process and apparatus for preparation of octachlorotrisilane

Abstract

The invention relates to a process and an apparatus for controlled preparation of octachlorotrisilane from monomeric chlorosilanes, by subjecting the chlorosilanes to a thermal plasma.

Claims

1. A process for preparing octachlorotrisilane, the process comprising subjecting chlorosilanes comprising at least one monomeric chlorosilane of formula I in the absence of hydrogen to a thermal plasma:
H.sub.xSiCl.sub.4−x  (I), where x is independently selected from 0, 1, 2 and 3.

2. The process according to claim 1, further comprising obtaining a mixture of octachlorotrisilane and hexachlorodisilane.

3. The process according to claim 1, further comprising isolating ultrahigh-purity octachlorotrisilane.

4. The process according to claim 1, further comprising obtaining octachlorotrisilane having a titanium content of less than 1 ppm by weight.

5. The process according to claim 1, wherein the the chlorosilanes are one or more of an ultrahigh-purity tetrachlorosilane, an ultrahigh-purity trichlorosilane, and an ultrahigh-purity dichlorosilane.

6. The process according to claim 1, wherein the process is performed in an apparatus comprising a gas discharge reactor, a first column, and a second column.

7. The process according to claim 6, wherein the first column is provided with a column inlet for removal of octachlorotrisilane upstream of the gas discharge reactor and the second column is provided with a column inlet for removal of low boilers downstream of the gas discharge reactor and a column outlet, the column outlet of the second colunm has a dedicated gas divider, and the gas divider has a dedicated recycle line which supplies the low boilers to the first column or to the gas discharge reactor as a return stream.

8. The process according to claim 7, wherein the gas divider has a shut-off, a valve, or other regulating unit.

9. The process according to claim 7, wherein the chlorosilane of the formula I is introduced into the gas discharge reactor or supplied to the first column in a mixture with hexachlorodisilane.

10. The process according to claim 9, wherein unconverted mixture of the chlorosilanes of the formula I and hexachlorodisilane leaving the gas discharge reactor via the second column are divided in the apparatus at the gas divider, a portion of the mixture is recycled as a return stream via the recyle line into the first column and conducted again through the gas discharge reactor, and high-purity or ultrahigh-purity octachlorotrisilane is obtained at the column outlet of the first column.

11. The process according to claim 10, wherein a molar ratio of trichlorosilane to tetrachlorosilane in the return stream is from 0.1:20 to 2:20.

12. The process according to claim 6, wherein a pressure of 300 to 800 mbar.sub.abs exists in the gas discharge reactor.

Description

(1) The invention is illustrated in detail hereinafter by the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

(2) FIG. 1: Mixture comprising octachlorotrisilane and hexachlorodisilane prepared by the process according to the invention, 99.34 MHz .sup.29Si NMR in DMSO.

(3) FIG. 2: Polychlorosilanes comprising hexachlorodisilane, octachlorotrisilane, tert-decachlorotetrasilane, n-decachlorotetrasilane and dodecachloropentasilane prepared by the process according to the invention, 99.34 MHz .sup.29Si NMR in DMSO. A=Si.sub.2Cl.sub.6, B=n-Si.sub.3Cl.sub.8, C=(Cl.sub.3Si).sub.3SiCl, D=n-Si.sub.4Cl.sub.10 and E=n-SiCl.sub.12.

(4) FIG. 3: Schematic diagram of the apparatus 0 comprising a gas discharge reactor 1 and a first column 2a and a second column 2b, and also a gas divider 5 and a recycle line 6.

(5) FIG. 4: Schematic diagram of the apparatus 0 with reboiler 8 and reactant feed 9, and also evaporator 10.

(6) FIG. 5: Schematic diagram of the apparatus 0 with reboiler 8, reactant feed 9, gas divider 5 and arrangement 11 comprising a condenser 13.

(7) FIG. 6: Schematic diagram of the arrangement 11 and gas divider 5

EXAMPLE 1

Preparation of Mixture of Octachlorotrisilane and Hexachlorodisilane

(8) The concentrations of the contaminants in the mixture obtained in accordance with the invention, measured in the .sup.29Si NMR, are shown in FIG. 1.

EXAMPLE 2

Preparation of Mixture of Polychlorosilanes

(9) The content of extraneous metals was measured by ICP-MS. The contaminants of the mixture obtained in accordance with the invention are shown in FIG. 2.

LIST OF REFERENCE NUMERALS

(10) 0 apparatus/plant 1 gas discharge reactor 2a first column 2b second column 3a upper column outlet of the first column 3b lower column outlet of the first column 4a lower column outlet of the second column 4b upper column outlet of the second column 5 condenser 6 recycle line 7 reservoir vessel 8 reboiler 9 reactant feed 10 evaporator 11 arrangement comprising condenser and regulating unit (return/removal) 12 line 13 condenser 14 shut-off/regulating unit