WO2015140027A1

WO2015140027A1 - Method for producing trichlorosilane

Info

Publication number: WO2015140027A1
Application number: PCT/EP2015/055138
Authority: WO
Inventors: Jens Felix Knoth; Andreas Hirschmann; Uwe Paetzold; Christoph Ruedinger
Original assignee: Wacker Chemie Ag
Priority date: 2014-03-18
Filing date: 2015-03-12
Publication date: 2015-09-24
Also published as: TW201536798A; DE102014205001A1

Abstract

The invention relates to a method for producing TCS through reaction of a gaseous starting material containing STC and hydrogen at a temperature of or above 900°C, where a gaseous product containing TCS is produced, characterized in that during the reaction at least one carbon-containing compound is present in the gaseous starting material, where the proportion by volume of the carbon-containing compounds in relation to the standard-conditions volume flow rate of hydrogen is from 10 ppm by volume to 10% by volume, where, unlike in the case of reaction of the gaseous starting material containing STC and hydrogen without addition of a carbon-containing compound to the gaseous starting material, the quantity of additional organochlorosilanes present in the resultant product mixture after condensation of silane fractions in the gaseous product is at most 200 ppm by weight.

Description

Process for the preparation of trichlorosilane

The invention relates to a process for the preparation of trichlorosilane. Trichlorosilane (TCS) is used to make polycrystalline silicon.

The production of TCS is usually carried out in a fluidized bed process of metallurgical silicon and hydrogen chloride. In order to produce high-purity TCS, followed by a distillation. It also falls as a byproduct

Silicon tetrachloride (STC) on.

The largest amount of STC occurs in the deposition of polycrystalline silicon.

Polycrystalline silicon is produced, for example, by means of the Siemens process. This polycrystalline silicon is deposited in a reactor on heated thin rods. As the process gas is used as a silicon-containing component

Halogensilane such as TCS used in the presence of hydrogen. In the

Implementation of TCS (disproportionation) in deposited silicon produces large amounts of STC.

From STC, for example, by reaction with hydrogen and oxygen at high temperatures in combustion chambers highly disperse silica can be produced.

However, the most economically interesting use of STC is the conversion to TCS. This is done by reaction of STC with hydrogen in TCS and

Hydrogen chloride. This makes it possible from the deposition

resulting by-product STC again TCS to produce and that TCS again to the deposition process to produce elemental silicon. There are two methods of conversion known: The first method, the so-called low-temperature conversion, is carried out in the presence of one or more catalysts. However, the presence of catalysts (eg Cu) can adversely affect the purity of the TCS and thus of the silicon deposited therefrom. A second method, the so-called high-temperature conversion, is an endothermic process with the formation of products being equilibrium-limited. In order to achieve significant TCS production at all, very high temperatures must be used in the reactor (> 900 ° C.).

Thus US 3933985 A describes the reaction of STC to TCS with hydrogen at temperatures in the range of 900 - 1200 ⁰ C and at a molar ratio H _2: SiCl ₄ of 1: 1 to 3: 1. Yields of 12-13% are described.

For these high-temperature processes, graphite was first used as a

Construction material used, due to the advantageous mechanical and chemical properties.

However, EP 0 294 047 A1 showed that upon contact of graphite with hydrogen at T> 500 ^° C., hydrocarbons such as methane and methylsilanes can be formed. To avoid this undesirable effect, it has been proposed to coat the graphite components with silicon carbide.

Also EP 1 454 670 B1 describes the reaction of hydrogen with

carbon-based engineering materials and graphite at temperatures of 400-1000 ° C and the resulting formation of methane, which

Contaminants in the product TCS leads.

EP 2 000 434 A2 describes an apparatus for the production of TCS from STC, with which it is possible to work at reaction temperatures of 800-1400 ° C., the conversion rate being increased at temperatures of 1200 ° C. and higher. It is further reported that by using a

Reaction vessel made of SiC-coated graphite (compared to a reaction vessel made of graphite) can be operated at much higher temperatures.

Also EP 2 008 969 A1 and EP 2 014 618 A1 disclose devices for

Production of TCS from STC at temperatures of 800-1400 ⁰ C. The

Devices can be constructed of SiC coated carbon which, as opposed to uncoated carbon, also allows reduced levels of methane, methylchlorosilane (MCS) and SiC impurities from the attack of chlorosilanes, hydrogen and HCl on the carbon. Thus, TCS can be produced with increased purity.

However, SiC-coated carbon-based materials have the disadvantage that with time hydrogen and / or chlorosilanes penetrate the SiC layer and to Damage to the graphite or the carbon-based construction materials can cause.

Therefore, EP 1 454 670 A1 claims SiC-based materials and, in particular, SiC and CVD-SiC as construction material for components in contact with the reaction gas at high temperatures. As a result, compared to the apparatuses made of carbon-based materials increased life of the apparatus is achieved.

US 3250322 A teaches the use of heat exchangers for corrosive atmospheres, which are composed of a thermally conductive base body on which a gas-tight SiC layer was applied.

DE 43 17 905 A1 claims a reactor for the hydrogenation of chlorosilanes at temperatures> 600 ° C. In this case, the reaction chamber and the heating elements made of SiC-coated carbon fiber composite material, which can reach higher temperatures and chemical destruction of carbon and graphite of the construction material avoid it. With SiC coated carbon composite materials as the construction material, improved resistance to cracking by pressure and stress can be achieved

Temperature stresses and destruction due to

Reactions can be achieved with the feed materials and corrosive by-products. Furthermore, it is shown that SiC-coated carbon composite materials to a much lesser extent for the formation of by-products such. Contribute methane.

EP 1 775 263 B1 discloses a process for the hydrogenation of chlorosilanes, which permits an in situ formation of SiC on the surface of the reaction chamber and of the heating elements and thereby avoids the introduction of impurities into the reaction and ultimately into the product. It was found that the heating elements coated in situ, despite increased temperatures, have a significantly longer service life than known heating elements. Analytical studies reveal a greatly reduced corrosion of the graphite and also significantly reduced levels of by-products from the reaction with graphite were found, for. B. Methyltrichlorosilane (MTCS)

DE 10 2009 047 234 A1 discloses a process for the production of

Methylchlorosilanes and TCS by reacting STC with mixtures of methane and hydrogen, wherein 20-95 mol% of methane based on the reactive gas consisting made of hydrogen and methane. Rapid cooling to a temperature below 200 ^° C. proves advantageous to reverse reactions

suppress. The dosage of methane should be chosen so that it does not cause any

Solid separation occurs. With this method, high yields of both MCS and TCS can be obtained at temperatures of 600-100 ° C.

DE 10 2011 005 643 A1 claims a device in which

hydrogen-containing chlorosilanes are produced under reduced Si-based solid deposits during operation of the device. In the device, at least one organochlorosilane (OCS) is reacted with hydrogen, at least temporarily, in which case additional HCl is added at least temporarily.

This is preferably carried out in one of the reaction spaces of the reactor

Hydrodehalogenation of STC generated with hydrogen. CH 430905 A discloses a process for the preparation of

High temperature heating elements made of SiC. In this case, a gas-tight SiC layer of a carbon or silicon compounds on the heating element

deposited gas. DE 10 2011 005 647 A1 claims a process for preparing at least one hydrogen-containing chlorosilane within a composite system by hydrogenating at least the educts STC and MTCS with hydrogen in a reactor operated under pressure from reactor tubes consisting of gas-tight ceramic material. The process makes it possible to produce hydrogen-containing chlorosilanes with efficient, as economical as possible use of STC-containing secondary streams and secondary streams containing MTCS. MTCS is produced as a by-product in relatively large quantities, in particular in the Müller-Rochow synthesis for the preparation of

Dimethyldichlorosilane as the most important raw material for the production of silicones. DE 10 201 1 002 436 A1 relates to a method for the production of TCS by

Reaction of at least hydrogen and an OCS in a pressure-driven reactor made of ceramic material. In mixture with the at least one

organic chlorosilane can additionally STC be reacted with hydrogen to trichlorosilane.

In the reaction, a hydrogen-containing educt gas and a starting material gas containing at least one organic chlorosilane and optionally an STC-containing

Reactant gas in a reactor by the addition of heat are reacted to form a trichlorosilane-containing product gas, wherein the OCS-containing Feedstock gas and / or the hydrogen-containing feed gas and / or the STC-containing educt gas are fed as pressurized streams in the pressure-operated reactor and the product gas is led out as a pressurized stream from the reactor. The molar ratio of hydrogen to the sum of OCS and STC is preferably in a range of 1: 1 to 8: 1. The reaction should be carried out at a pressure of 1 to 10 bar and / or a temperature in the range of 700 ° C to 1000 ° C and / or a gas stream.

In this implementation, however, create significant amounts of substance

carbonaceous impurities in the product, so up to 25 wt .-% MTCS and up to 2 wt .-% methyldichlorosilane (MDCS) are found, in particular the latter is difficult to separate from TCS and significantly reduces the cost of the process.

In the prior art it is known that in a hydrogenation of chlorosilanes at high reactor temperatures at which a chemical attack of the

Reaction gases (eg TCS, HCl, H ₂ , STC) is to be expected, ceramic materials or graphite, possibly coated with SiC, quartz glass or SiC should be used.

However, these materials are subject to corrosion at temperatures above 900 ° C, in which the conversion proceeds with very high yields, which greatly reduces the service life of the reactors.

DE 19949936 A1 describes a method for protecting components from graphite and carbon materials when used in hydrogen atmospheres

Temperatures above 400 ⁰ C, characterized in that the

Hydrogen atmospheres as a function of the prevailing temperature and the pressure of methane in the ratio of the stoichiometric equilibrium between hydrogen and methane is mixed. The experiments are carried out at a pressure of 10 bar and an oven temperature of 1 100 ⁰ C. Under these

Conditions is the stoichiometric equilibrium at 95% hydrogen to 5% methane. However, in addition to hydrogen, chlorosilanes and HCl, which also have a corrosive effect, are present in a conversion reaction.

The object of the present invention is to provide a process for the production of TCS by means of thermal hydrogenation of a reactant gas containing STC, which enables a high yield of TCS with an increased cost-efficiency compared to the prior art, by simultaneously reducing the corrosion of the reactor material becomes. The object is achieved by a method for the production of TCS by

Reacting a reactant gas containing STC and hydrogen at a temperature of greater than or equal to 900 ° C, wherein a product gas containing TCS is formed, characterized in that during the reaction at least one

carbon-containing compound is present in the educt gas, wherein a volume fraction of the carbon-containing compounds based on a standard volume flow of hydrogen is 10 vol. ppm to 10 vol .-%, wherein after condensation of

Silane shares in the product gas over a reaction of the educt gas containing STC and hydrogen without the addition of a carbon-containing compound to

Eduktgas a maximum of 200 ppmw of additional Organochlorsiianen in the resulting product mixture are included.

The reaction results in a product gas containing TCS, organohalosilanes, unreacted STC and hydrogen, as well as HCl. In the condensation, silane components and hydrogen / HCl are separated. The result is a condensate containing chlorosilanes and organochlorosilanes, with respect to a reaction of the

Eduktgases containing STC and hydrogen without adding a carbon-containing compound to the reactant gas at most 200 ppmw of additional Organochlorosian in the product mixture (condensate) are included.

The invention provides for a conversion of STC at a high temperature at which there is a defined volume fraction of a carbon-containing compound.

The carbonaceous compound may be gaseous. Preferably, a carbon-containing compound is used which is present at temperatures of <200 ° C in the gaseous state. However, it may also be carbon in finely divided particulate form, e.g. to act on carbon nanoparticles. It is also preferable to add carbon both in gaseous and in particulate form. Essential for the success of the invention is not to increase the proportion of carbonaceous impurities in the condensate significantly. Therefore, such carbon-containing compounds are preferably used, which do not lead to the formation of new impurities in the product (but already in

Product mixture would be included without additives) and more preferably those which can be easily separated again from the target product. Preferably, the at least one carbon-containing compound is selected from the group consisting of linear, branched and cyclic alkanes and

Organochlorosilanes. Particularly preferred is the use of linear alkanes or OCS.

A preferred embodiment of the method provides that the

containing carbonaceous compound MTCS or MDCS. Very particularly preferred is the use of methane.

Furthermore, it is preferred to use methane and an organochlorosilane.

The volume fraction of the carbon-containing compounds (based on the

Standard volume flow of hydrogen) is from 10 ppm by volume to 10% by volume, preferably from 50 ppm by volume to 5% by volume, more preferably from 100 ppm by volume to 1% by volume (= 10000% by volume). ppm). Very particular preference is given to a volume fraction of 500 ppm by volume - 7500 ppm by volume. In a preferred embodiment of the invention, the mass fraction of carbon based on the mass flow of hydrogen and carbon-containing compound (meaning here the total mass flow of hydrogen and the carbon-containing compound) is 60 to 350,000 ppmw.

Preferably, the mass fraction of carbon is based on the

Mass flow of hydrogen and carbon-containing compound 300 to 220,000 ppmw, more preferably 600 to 56,000 ppmw and most preferably 3000 - 42,500 ppmw (ppmw = part per million by weight).

Preferably, in the product mixture in comparison to the resulting in a reaction of STC and hydrogen, in which no additional carbonaceous compounds are supplied, resulting product mixture contains less than 50 ppmw, more preferably less than 10 ppmw of additional organochlorosilanes.

Preferably, the product mixture formed during the reaction and condensation of the silane components according to the invention contains a maximum of 500 ppmw, preferably 200 ppmw, more preferably at most 100 ppmw, most preferably at most 50 ppmw of organochlorosilanes. In a preferred embodiment, the method is carried out in a device which consists entirely of SiC or SiC-coated materials or SiC composite materials. Particularly preferred is a device made entirely of SiC.

Preferably, the device provides a heat exchanger, the reactant gas heated by the countercurrent principle by product gas. In addition, the apparatus preferably provides a reactor having a reaction zone in which reactant gas containing STC, hydrogen and the carbonaceous compound is introduced, the reaction zone being heated by a heater located outside the reaction zone. The reactor and heat exchanger preferably form a single, gas-tight workpiece, wherein the workpiece consists of one or more ceramic materials selected from the group consisting of silicon carbide, silicon nitride, graphite, coated with SiC graphite and quartz glass.

The device preferably comprises channels or capillaries, with only product gas flowing in one part of the capillaries or channels and only educt gas in the other part. The capillaries can also be arranged in the form of a shell-and-tube heat exchanger. In this case, one gas flow flows through the tubes (capillaries) while the other gas flow flows around the tubes.

Preferably, the gas in the reaction zone (under the reaction zone is the region in which the temperature is constant (+ -50 ° C)) a short hydrodynamic residence time greater than or equal to 0.1 ms and less than or equal to 250 ms, preferably greater than or equal to 0.2 ms and less than or equal to 100 ms, more preferably greater than or equal to 0.3 ms and less than or equal to 10 ms, very particularly preferably greater than or equal to 0.4 ms and less than or equal to 2 ms.

It is advantageous if the resulting product gas containing TCS is cooled, with the proviso that it is cooled to a temperature of 700-900 ° C. within 0.1-35 ms.

Surprisingly, by the addition of the carbonaceous compound, the extent of corrosion in devices made of carbon and graphite materials, carbon fiber composites, SiC coated carbon fiber composite materials, SiC based materials (including but not limited to: CMC (ceramic matrix composite)). , ceramic SiC, CVD-SiC)

be reduced without significantly increasing the level of OCS in the condensate. Particularly preferably, the method is implemented so that the additives of the carbonaceous compound have no influence on the proportion of TCS formed (change less than 0.5 wt .-% in the condensate). The invention makes it possible, the stability of the reactor material (and thus the

Service life of the reactor) at high temperatures significantly, namely by at least 10%, to extend, whereby high equilibrium conversions with long service lives and high product quality allow increased efficiency of the process.

In a further particularly preferred embodiment of the process, the hydrogenation of STC is carried out in a composite. Here, the to

Hydrogenation used hydrogen from another process, for example, but not limited to hydrogen from the synthesis of TCS starting from silicon.

Preferably, the required carbonaceous compound is already contained in the circulation STC wholly or partly in the form of methane in a composite already in the cycle hydrogen and / or in the form of organochlorosilanes.

STC-containing secondary streams can be produced during the production of TCS from metallurgical silicon. Significant amounts of STC as a by-product can also be obtained in the deposition of polycrystalline silicon from TCS in a Siemens reactor. STC from such secondary streams can after workup by means of

Condensation and subsequent distillation of the composite material, in particular the conversion to TCS, fed (circulatory STC).

As a further by-product is formed in the production of TCS from metallurgical silicon hydrogen, which can be separated by subsequent condensation and the conversion in the composite process can be supplied as starting material. In the

Deposition of polycrystalline silicon from TCS in a Siemens reactor produces unreacted hydrogen. This too can after condensation

Material composite (circulating hydrogen) are supplied.

The invention is preferably used in processes under elevated pressure, preferably at an outlet pressure of greater than or equal to 5 bar, more preferably at an outlet pressure greater than or equal to 6 bar, most preferably at an outlet pressure of greater than or equal to 10 bar. The reaction temperature is preferably greater than or equal to 1000 ⁰ C, more preferably greater than or equal to 1200 ⁰ C and very particularly preferably greater than or equal to 1300 ° C. There is no separation of solids and / or liquids in the reactor. In particular, there is no SiC deposition. This can be ruled out that it can lead to clogging of eg heat exchangers.

Example and Comparative Example

The corrosion on SiC reactors manifests itself in a reduction in the pressure drop across the reactors (increase in the hydraulic diameter). This can be measured. In addition, X-ray tomographs were performed on the SiC reactors, which can clearly prove the corrosion in the reactor.

In each case, a conversion was carried out at 1325 ° C. in the example and comparative example, with the same amounts of STC and hydrogen being fed from the material cycle.

Comparative example

The conversion was carried out at 1325 ° C in a SiC reactor in which a mixture of 676 Nml / h STC and 264 Nl / h (Nl: standard liters) of hydrogen was fed.

It was worked without further additives such as methane. Over a period of operation of 48 hours, the pressure loss was reduced by 11.0%, and the MCS content in the condensate was about 5 ppm by weight.

Example The conversion was carried out at 1325 ° C in a SiC reactor into which a mixture of 676 Nml / h STC and 264 Nl / h (Nl: standard liters) of hydrogen was fed. An addition of 1500 vol. Ppm (based on the

Standard hydrogen volume flow) of methane into the reactor.

Over a service life of 340 h, the pressure loss was reduced by 0.8%, and the MCS content in the condensate was about 7 ppm by weight.

Compared to the comparative example, there was thus only an increase in the MCS content in the product gas of only about 2 ppm by weight.

Even after a 7-fold operating time (340 h vs. 48 h), no noticeable reduction in the pressure loss can be detected, which underpins the effect of adding methane to the educt gas.

Claims

claims

1 . Process for the preparation of TCS by reacting a reactant gas

containing STC and hydrogen at a temperature of greater than or equal to 900 ° C, wherein a product gas containing TCS is formed, characterized in that during the reaction at least one carbon-containing compound is present in the educt gas, wherein a volume fraction of the carbon-containing

Compounds based on a standard volume flow of hydrogen 10 vol.-ppm to 10 vol .-%, wherein after condensation of silane in the product gas over a reaction of the educt gas containing STC and hydrogen without addition of a carbon-containing compound to the educt gas a maximum of 200 ppmw of additional organochlorosilanes in contained product mixture are contained.

2. The method of claim 1, wherein the carbonaceous compound is gaseous at a temperature of less than or equal to 200 ° C or wherein it is in particulate form.

3. The method of claim 1 or claim 2, wherein the carbonaceous compound is selected from the group consisting of alkanes and

Organochlorosilanes.

4. The method according to any one of claims 1 to 3, wherein the carbonaceous

Compound contains MTCS or MDCS.

5. The method according to any one of claims 1 to 4, wherein the carbonaceous

Compound contains methane.

6. The method according to any one of claims 1 to 5, wherein the reaction at an outlet pressure of greater than or equal to 5 bar, preferably greater than or equal to 6 bar and particularly preferably greater than or equal to 10 bar.

7. The method according to any one of claims 1 to 6, wherein the volume fraction of

carbonaceous compounds based on the standard volume flow

Hydrogen 50 vol. Ppm to 5 vol .-%, preferably 100 vol. Ppm to 1 vol .-% and more preferably 500 vol. Ppm - 7500 vol ppm.

8. The method according to any one of claims 1 to 7, wherein a mass fraction of

Carbon based on a mass flow of hydrogen and the

carbon-containing compound 60 to 350,000 ppmw, preferably 300-220,000 ppmw, more preferably 600-56,000 ppmw and most preferably 3000-42,500 ppmw.

9. The method according to any one of claims 1 to 8, wherein in the product mixture in

Compared to that in a reaction of STC and hydrogen, in which no additional carbonaceous compounds are supplied, resulting product mixture less than 50 ppmw, preferably less than 10 ppmw of additional organochlorosilanes are included.

10. The method according to any one of claims 1 to 9, wherein the product mixture obtained in the reaction and subsequent condensation contains a maximum of 200 ppmw, preferably at most 100 ppmw and more preferably at most 50 ppmw of organochlorosilanes.

1 1. A process according to any one of claims 1 to 10, wherein the reaction is carried out in a reaction zone of a reactor, the reaction zone being heated by a heater located outside the reaction zone, the

Reactant gas is heated by means of a heat exchanger according to the countercurrent principle by the product gas, wherein reactor and heat exchanger form a single, gas-tight workpiece, the workpiece of one or more ceramic materials selected from the group consisting of

Silicon carbide, silicon nitride, graphite, SiC coated graphite and

Quartz glass exists.

12. The method according to claim 11, characterized in that the hydrodynamic residence time of educt gas in the reaction zone 0.1 - 250 ms, preferably 0.2 - 100 ms, more preferably 0.3 - 10 ms, most preferably 0.4 - 2 ms.

13. The method according to any one of claims 1 to 12, wherein the reaction at a temperature of greater than or equal to 1000 ° C, preferably greater than or equal to 1200 ° C and particularly preferably greater than or equal to 1300 ⁰ C takes place.

14. The method of claim 13, wherein the resulting product gas containing TCS is cooled, with the proviso that is cooled to a temperature of 700-900 ° C within 0.1 to 35 ms