Method for the preparation of silanes

Abstract

The invention relates to a process for preparing dimeric and/or trimeric silanes by conversion of monosilane in a plasma and to a plant for performance of the process.

Claims

1. A process for preparing a dimeric and/or trimeric silane of the general formula I: ##STR00003## wherein n=0 or 1, comprising: i) subjecting a reactant stream comprising monosilane of the general formula II ##STR00004## and hydrogen, ii) to a gas discharge, and iii) obtaining the dimeric and/or trimeric silane of the formula I from a resulting phase, and setting a defined ratio of a partial hydrogen pressure to a partial pressure of a silane which is gaseous under a condition selected in the resulting phase; wherein the defined ratio in process step iii) of the partial hydrogen pressure to the partial pressure of the gaseous silanes is set by a hydrogen-permeable membrane.

2. The process according to claim 1, wherein the pressure in process step iii) is elevated relative to the pressure in process stage ii).

3. The process according to claim 1, wherein the resulting phase in process step iii) has a pressure of 1 bar.sub.ab to 100 bar.sub.abs.

4. The process according to claim 1, wherein the monosilane in process step ii) is subjected to the gas discharge in the presence of hydrogen at a pressure between 0.05 mbar.sub.abs and 15,000 mbar.sub.abs.

5. The process according to claim 1, wherein the gas discharge in process step ii) is effected at a pressure between 0.1 mbar.sub.abs and 1,000 mbar.sub.abs.

6. The process according to claim 1, wherein the gas discharge in process step ii) is effected at a temperature between 60 C. and 10 C.

7. The process according to claim 1, wherein the reactant stream has a defined ratio of hydrogen and monosilane in percent by volume (% by vol.) of 15:1 to 1:5.

8. The process according to claim 1, wherein the reactant stream in step ii) is exposed to a nonthermal plasma.

9. The process according to claim 1, wherein the membrane is permeable to hydrogen and essentially impermeable to silanes.

10. The process according to claim 1, wherein said membrane comprises at least one of the following materials: quartz, metal, metallic alloy, ceramic, zeolite, organic polymer and/or a composite membrane having an at least two-layer structure comprising one or more of the aforementioned materials.

11. The process according to claim 1, wherein the dimeric silane is obtained.

12. The process according to claim 1, wherein the trimeric silane is obtained.

13. The process according to claim 1, wherein a mixture of the dimeric and the trimeric silanes is obtained.

Description

EXAMPLE 1

(1) Monosilane is vaporized continuously from a pressurized gas bottle 9 by means of a pressure regulator via the reactant feed 12 into the reactor 1 and conducted through a gas discharge zone comprising dielectric. The nonthermal plasma is operated in the reactor at 10 C. and at 60 mbar.sub.abs. The SiH bond of the monosilane in the reactant stream composed of 10% by volume of monosilane and 90% by volume of hydrogen is selectively excited to form silyl radicals, which react to form disilane or trisilane and form the resulting phase. After increasing the pressure of the resulting phase to about 2.5 bar.sub.abs, it is passed through a condenser 3 cooled to about 0 C., in order to condense disilane and trisilane, which can run off into the crude product vessel 4 which is at a controlled temperature of 40 C. The remaining gaseous resulting phase is run past one side of the membrane 5 through a line 10. Hydrogen in the resulting phase diffuses through the membrane 5 and can be removed via the line 15. At the membrane, a defined ratio of the partial hydrogen pressure to the partial pressure of the monosilane which is gaseous under the conditions selected is set in the resulting phase. As a result of this measure, the resulting phase becomes a reactant stream which is fed again to the gas discharge zone comprising dielectric in the reactor, optionally after metered addition of further monosilane. In the crude product vessel, disilane is enriched in the mixture having a proportion of trisilane, which are pumped by the product pump 16 to the distillation column 17, in order to be fractionally distilled therein.

(2) By continuous fractional distillation, ultrahigh-purity disilane was drawn off as a low boiler at the top of the column 17 and trisilane as a high boiler at the bottom of the column.

(3) The general process regime of Example 1 is not limited to the specified process parameters, but can be generalized in accordance with the description.

(4) FIG. 1 and FIG. 2 show a schematic diagram of an inventive plant 0 for performance of the process according to the invention.

(5) FIG. 3 shows a diagram of the hydrogen permeability of various membrane materials.

LIST OF REFERENCE NUMERALS

(6) 0 plant 1 reactor 2 compressor 3 condenser 4 crude product outlet or crude product vessel 5 membrane 6 vacuum pump 7 inverter for plasma production 8 hydrogen sourcestartup of the process 9 monosilane source 10 line/resulting phase 11 line/reactant feed 12 line/reactant feed 13 line/monosilane 14 line/resulting phase 15 line/hydrogen 16 product-conveying pump 17 columnfractional distillation 18 lineinert gas for hydrogen removal