EP2686099A1

EP2686099A1 - Combined method for the production of hydrogen-containing chlorosilanes

Info

Publication number: EP2686099A1
Application number: EP12703737.2A
Authority: EP
Inventors: Yücel ÖNAL; Guido Stochniol; Ingo Pauli; Norbert Schladerbeck
Original assignee: Evonik Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2011-03-16
Filing date: 2012-01-27
Publication date: 2014-01-22
Also published as: WO2012123159A1; JP2014519460A; TW201249744A; CA2829701A1; CN103402623A; KR20140008372A; US20140212352A1; DE102011005647A1

Abstract

The invention relates to a method for producing a product gas mixture containing hydrogen-containing chlorosilanes within a combined method by hydrogenating silicon tetrachloride and organochlorosilanes, in particular methyl trichlorosilane, which are obtained as byproducts in the combined method, with hydrogen in a pressurized hydrogenation reactor comprising one or more reaction chambers, each of which consists of a reactor tube made of gas-tight ceramic material. The product gas mixture is reprocessed, and at least a portion of at least one product of the product gas mixture is used as feedstock in the hydrogenation process or as feedstock in another process within the combined method. The invention further relates to a combined system suitable for carrying out the combined method.

Description

COMPOUND PROCESS FOR THE PRODUCTION OF HYDROGEN HALFEN CHLOROILANES

The invention relates to a process for the preparation of a product gas mixture containing hydrogen-containing chlorosilanes within a composite process by hydrogenation of the by-product obtained in the composite process

Silicon tetrachloride (STC) and organochlorosilane (OCS), in particular

Methyltrichlorosilane, with hydrogen in a pressure-operated hydrogenation reactor, the one or more reaction chambers, each consisting of a reactor tube made of gas-tight ceramic material comprises, wherein the

Worked up product gas mixture and at least a portion of at least one product of the product gas mixture is used as a reactant of the hydrogenation or as a precursor of another method within the composite process. Furthermore, the invention relates to a composite system which for carrying out the

Composite method is suitable.

Hydrogen-containing chlorosilanes and in particular trichlorosilane (TCS) are important raw materials for the production of hyperpure silicon, which is needed in the semiconductor and photovoltaic industries. The demand for TCS has risen steadily in recent years and for the foreseeable future a further increase in demand is forecast.

The separation of hyperpure silicon from TCS is carried out according to the technical standard from the gas phase in a Chemical Vapor Deposition (CVD) process according to the Siemens method. The TCS used is usually prepared by a chlorosilane process, i. H. Reaction of technical silicon with HCl (hydrochlorination of Si) at temperatures around 300 ° C in one

Fluidized bed reactor or recovered at temperatures around 1000 ° C in a fixed bed reactor and subsequent workup by distillation of the product mixture.

Depending on the choice of process parameters, both in the CVD process of

Pure silicon production and incurred in the chlorosilane process, larger amounts of silicon tetrachloride (STC) as a byproduct. In addition to STC will be at this process by reaction of organic impurities with chlorosilanes as further by-products in smaller amounts organochlorosilanes (OCS),

especially methyldichlorosilane (MHDCS) and methyltrichlorosilane (MTCS). Furthermore, organochlorosilanes are deliberately obtained by Muller-Rochow synthesis of silicon and alkyl chlorides. In the production of dimethyldichlorosilane as the most important starting material for the production of silicone from Si and chloromethane, MTCS is produced as coproduct in significant quantities.

In view of the increasing demand for TCS and hyperpure silicon it would be

economically very interesting to make these sidestreams of STC and organochlorosilanes, in particular the MTCS sidestreams of a Müller-Rochow synthesis usable for the semiconductor and photovoltaic industry.

Thus, various methods for converting STC to TCS have been developed. According to the technical standard, a thermally controlled process is used for the hydrodehalogenation of STC to TCS, in which the STC is passed together with hydrogen into a graphite-lined reactor and reacted at temperatures of 1100 ° C. and higher. Due to the high temperature and the proportional hydrogen content, the equilibrium position is shifted to the product TCS. The product gas mixture is passed out of the reactor after the reaction and separated in complex processes.

In recent years, this process improvements have been proposed, in particular such. For example, in US 5,906,799, the use of carbon-based materials with a chemically inert coating, such as SiC, to the lining of the reactor. In this way, a degradation of the construction material and contamination of the product gas mixture due to reactions of the carbon-based material with the chlorosilane / H ₂ gas mixture can be largely avoided.

DE 102005046703 A1 further describes the in-situ SiC coating of a graphitic heating element in one of the hydrodehalogenation upstream Step. The arrangement of the heating element in the interior of the reaction chamber in this case increases the efficiency of the energy input of the electrical resistance heater.

However, disadvantageous in the above method is that partially expensive coating processes are required. In addition, the heat input required for the reaction process is due to the use of carbon-based construction materials by means of electrical resistance heaters, which in the

Compared to a direct heating by means of natural gas is uneconomical. At the high reaction temperatures required, typically 1000 ° C. and higher, undesired silicon deposits also occur which necessitate regular purification of the reactor.

The main drawback, however, is the performance of a purely thermal reaction, without a catalyst, which makes the above processes very inefficient overall. Accordingly, various methods for

catalytic hydrodehalogenation of STC has been developed.

In a previous separate application, a process for the hydrodehalogenation of SiCl ₄ to TCS is described. In this case, the reaction is advantageously carried out under pressure and in the presence of a catalyst which comprises at least one active component selected from the metals Ti, Zr, Hf, Ni, Pd, Pt, Mo, W, Nb, Ta, Ba, Sr, Ca, Mg, Ru, Rh, Ir or combinations thereof or their silicide compounds. This procedure allows high space-time yields of TCS with almost thermodynamic conversion and high selectivity. The reactor contains one or more preferably coated with the catalyst reactor tubes, which consist of gas-tight ceramic material. In particular, find reactor tubes made of SiC, S13N4 or mixed systems thereof use, which are sufficiently inert, corrosion-resistant and gas-tight even at the high required reaction temperatures of 900 ° C. The heat input for the implementation can be made as a result of this choice of material economically by arranging the reactor tubes in a combustion chamber which is heated by combustion of natural gas. This reactor system has also been used to hydrogenate MTCS to a chlorosilane mixture comprising dichlorosilane (DCS), TCS and STC at process conditions typically required for hydrodechlorination of STC to TCS, allowing for high space-time yield and Selectivity to TCS. Other by-products are methane, HCl and MHDCS.

Significant sales with respect to MTCS, however, are obtained only from a temperature of at least 800 ° C. As an undesirable side effect it comes at these high temperatures for the disturbing separation of solids, which in

Essentially made of silicon. However, it was found that through

Combining the hydrogenation of MTCS with the hydrodehalogenation of STC solid deposits in the reactor during operation can be significantly reduced and also the yield of TCS can be increased. For this purpose, suitable advantageous reactor interconnections and modes of operation are the subject of a parallel application. In the process described, MTCS and STC were used as commercially pure substances. For a large-scale process, however, the supply of low-cost raw materials is preferable. An economical use of as a by-product in a CVD process of

Purest silicon recovery, in the hydrochlorination of Si and / or a Muller-Rochow synthesis resulting silicon tetrachloride and / or methyltrichlorosilane in a composite process would therefore be desirable.

The object of the present invention was therefore to provide a commercially applicable composite process for the preparation of hydrogen-containing chlorosilanes with efficient, most economical use of these silicon tetrachloride-containing secondary streams and methyltrichlorosilane-containing secondary streams.

To solve this problem, it was found that STC-containing side streams of a CVD process of ultrapure silicon recovery and / or a process for the hydrochlorination of Si and MTCS-containing side streams in particular a Müller-Rochow synthesis integrated in the composite process

Hydrogenated reactor reacted with hydrogen to form hydrogen-containing chlorosilanes and fed after separation of the product gas mixture, the individual product streams of economic re-use, preferably in the composite process can be. In particular, the process allows an increase in the yield of economically valuable intermediate and end products, in particular TCS and the hyperpure silicon available therefrom for semiconductor and photovoltaic applications.

The basis for the present invention is the above-mentioned

Reactor concept of a co-owned separate application relating to a process for the combined hydrogenation of MTCS and hydrodehalogenation of STC to hydrogen-containing chlorosilanes in a pressure-operated reactor system comprising catalytically coated reactor tubes consisting of gas-tight ceramic material. With this, with a suitable choice of the reactor connection and the reaction parameters such as temperature, pressure, residence time and

Substance ratios of the reactants an efficient process for the hydrogenation of MTCS and hydrodehalogenation of STC to hydrogen-containing chlorosilanes with high space-time yield and selectivity with respect to TCS can be represented. The option of an economic heat input by arranging the gas-tight ceramic reactor tubes as reaction chambers in a fuel chamber fired with fuel gas, which is obtained as a by-product in the composite process, represents a further advantage of the method.

The solution according to the invention of the above-mentioned object, including preferred embodiments, will now be described.

The invention relates to a process for the preparation of a

Product gas mixture comprising at least one hydrogen-containing chlorosilane within a composite process by hydrogenating at least the educts of silicon tetrachloride and methyltrichlorosilane with hydrogen in a one or more reaction chambers comprising hydrogenation, wherein the method additionally a workup of the product gas mixture by separating at least a portion of at least one product and the use of at least one part at least one of the optionally separated several products as starting material of

Hydrogenation or as educt of at least one other method within the composite process, characterized in that the hydrogenation reactor under Pressure is operated and the one or more reaction chambers each consist of a reactor tube of gas-tight ceramic material.

The term "hydrogenation" or "hydrogenation reactor" in the context of the present invention, a hydrodehalogenation reaction such as the reaction of STC with hydrogen to hydrogen-containing chlorosilanes and / or a hydrogenation reaction such as the reaction of MTCS with hydrogen to hydrogen-containing chlorosilanes or Reactor for carrying out this

To understand reactions. The at least one other process in the composite process according to the invention comprises at least one process selected from the group comprising a process for the hydrochlorination of silicon, a process for the deposition of silicon from the gas phase and a process for carrying out a Muller-Rochow synthesis.

In the context of the present invention, a "hydrochlorination of silicon" is to be understood as meaning a process in which Si is reacted with HCl with introduction of heat into chlorosilanes. "Deposition of silicon from the gas phase" in the context of the present invention refers to Process in which elemental silicon is deposited by decomposition reaction of a gaseous Si-containing compound. Furthermore, in the context of the present invention, a "Mueller-Rochow synthesis" is a process for the preparation of

Alkylhalogensilanen by catalytic conversion of at least one

Alkyl halide, preferably methyl chloride to understand with Si.

In the abovementioned other methods, STC-containing and / or OCS- or MTCS-containing secondary streams may be obtained.

Silicon tetrachloride-containing secondary streams can be obtained in particular in the hydrochlorination of technical silicon to obtain TCS. The technical silicon used here is of low purity and will

usually by reduction of silica sand with coke in the electric

Arc furnace produced. The hydrochlorination may be according to the prior art known methods, for. B. in a fixed bed-like reactor or a

Fluidized bed reactor can be carried out with Si as a fixed or fluidized bed, depending on the reactor type, the temperature between 300 ° C (fluidized bed reactor) and about 1000 ° C (fixed bed reactor) is set. Advantageously, the

Hydrochlorination carried out in the fluidized bed process to increase the yield with respect to TCS. As a further by-product formed in the hydrochlorination of hydrogen, which can be separated by subsequent condensation and fed, for example, the pressurized hydrogenation reactor in the composite process as a reactant. The separation of the obtained from the hydrochlorination

Product mixture of chlorosilanes, in particular for the isolation of high-purity TCS, can be carried out by distillation.

On the other hand, significant amounts of by-product silicon tetrachloride may also be present in the deposition of Si from the gas phase, particularly in the

Deposition of high purity silicon from TCS in a CVD process

Incurred by Siemens technology. This process typically reduces high purity TCS with hydrogen at temperatures around 1100 ° C. Polycrystalline high-purity Si grows here on thin silicon rods from the gas phase. From the silicon rods can after their growth silicon single crystals for the semiconductor and photovoltaic industry z. Example by means of the zone melting process or the Czochralski process. In the CVD deposition of Si accumulating STC can be prepared by working up z. B. by condensation and

be separated subsequent distillation of the gaseous product mixture. HCl formed as another by-product can be used for the hydrochlorination of Si.

MTCS is produced as a by-product in larger quantities, in particular in the Müller-Rochow synthesis, for the production of dimethyldichlorosilane as the most important raw material for the production of silicones. Here, technical silicon is typically reacted with methyl chloride in the presence of Cu-based catalysts at temperatures of 280 to 320 ° C in fluidized bed or fluidized bed reactors. In addition to the main product, dimethyldichlorosilane, especially MTCS, trimethylchlorosilane and MHDCS are formed. The different chlorosilanes can be removed by distillation Workup of the product mixture are isolated. Minor sidestreams containing MTCS also occur in the hydrochlorination of Si, as organic

Impurities with chlorosilanes preferred to Organochlorverbindungen,

especially MHDCS and MTCS.

The STC- and / or MTCS-containing product mixtures from the hydrochlorination of Si, the deposition of Si from the gas phase and / or from a Müller-Rochow synthesis can thus be carried out according to methods known in the art, such as by condensation, distillation and / or or absorption, such that STC in the STC-containing side streams and MTCS in the MTCS-containing ones

Secondary streams are present in the purest possible form and / or mixtures.

All variants of the composite process according to the invention have in common that at least part of the STC and / or MTCS by-product used as educt of the hydrogenation is at least one of the abovementioned other processes.

The other processes preferably comprise a process for the hydrochlorination of silicon and / or a process for the deposition of silicon from the gas phase in which STC-containing side streams are obtained and a process for carrying out a Muller-Rochow synthesis in the MTCS-containing side streams.

In the process according to the invention, the secondary streams containing the STC and the secondary streams containing MTCS can be collected in each case in a reservoir and fed therefrom, with the addition of hydrogen, to the hydrogenation reactor in the composite process.

In all process variants of the invention, the methyltrichlorosilane as methyltrichlorosilane educt gas and / or the silicon tetrachloride as

Siliziumium tetrachloride-containing educt gas and / or the hydrogen as

hydrogen-containing reactant gas passed as pressurized streams into one or more reaction chambers of the hydrogenation reactor and there by supplying

Heat are reacted to form at least one product gas mixture containing at least one hydrogen-containing chlorosilane. The gas-tight ceramic material from which the reactor tubes of the hydrogenation reactor are preferably selected from SiC or S 13N4, or mixed systems (SiCN) thereof optionally wherein at least one reactor tube is filled with packing of the same material. Particular preference is given to using SSiC (pressure-sintered SiC), SiSiC (silicon-infiltrated SiC) or nitrogen-bonded SiC (NSiC). These are pressure stable even at high temperatures, so that the reaction of STC and MTCS with hydrogen can be operated at several bar pressure. Furthermore, they also have sufficient corrosion resistance at the required reaction temperatures of more than 800 ° C. In another

Embodiment, the genanten materials may be coated by a thin SiO 2 layer in the pm range, which forms an additional corrosion protection layer.

In a particularly preferred embodiment of the invention

Method are the inner walls of at least one reactor tube and / or at least a portion of the packing coated with at least one reaction of MTCS and STC with H ₂ to hydrogen-containing chlorosilanes catalyzing material. In general, the tubes can be used with or without a catalyst, wherein the catalytically coated tubes represent a preferred embodiment, since suitable catalysts lead to an increase in the reaction rate and thus to an increase in the space-time yield. If the fillers are coated with a catalytically active coating, it may be possible to dispense with the catalytically active internal coating of the reactor tubes. However, it is also preferable in this case for the inner walls of the reactor tubes to be included in the coating, since in this way the catalytically usable surface area is increased in comparison to purely supported catalyst systems (for example by means of a fixed bed).

If the inner walls of the reactor tubes and / or an optionally used fixed bed are coated with a catalyzing material, this is the case

catalyzing material preferably composed of a composition comprising at least one active component selected from the metals Ti, Zr, Hf, Ni, Pd, Pt, Mo, W, Nb, Ta, Ba, Sr, Ca, Mg, Ru, Rh, Ir or Combinations thereof or theirs

Silicide compounds, if any exist. In addition to the at least one active component, the composition often still contains an or a plurality of suspending agents and / or one or more auxiliary components, in particular for stabilizing the suspension, for improving the

Storage stability of the suspension, to improve the adhesion of the suspension on the surface to be coated and / or to improve the application of the suspension to the surface to be coated. The application of the catalytically active coating on the inner walls of the reactor tubes and / or the

optionally used fixed bed can be carried out by applying the suspension to the inner walls of the one or more reactor tubes and / or the surface of the packing, drying the applied suspension and then annealing at a temperature in the range of 500 ° C to 1500 ° C under inert gas or hydrogen ,

The at least one reaction tube is usually arranged in a heating chamber. The introduction of the heat required for the reaction can by combustion of a fuel gas, in particular from within the

Combined natural gas, take place in the heating chamber. In order to achieve a uniform temperature control when heating by means of fuel gas and to avoid local temperature peaks on the reactor tubes, the burner should not be aimed directly at the pipes. For example, they can be distributed and aligned over the heating chamber so that they point into the free space between parallel reactor tubes.

To increase energy efficiency, the hydrogenation reactor can also be connected to a

Heat recovery system to be connected. In a special

Embodiment for this purpose one or more of the reactor tubes on one side

closed and each contain a gas-supplying inner tube, which preferably consists of the same material as the reactor tubes. Between the closed end of the respective reactor tube and the pointing to this opening of the inner tube, this is a case

Flow reversal. In this arrangement, each heat from between

Inner wall of the reactor tube and the outer wall of the inner tube flowing product gas mixture transferred by thermal conduction of the ceramic inner tube to the educts flowing through the inner tube. Also the integrated Heat exchanger tube may be at least partially coated with the above-described catalytically active material.

The disruptive deposition of Si-based solids, which typically occurs in the reaction of organochlorosilanes such as MTCS with H ₂ at reaction temperatures above 800 ° C., can advantageously be significantly reduced by suitable combination with the hydrodehoiogenation of STC with hydrogen during the operation of the hydrogenation reactor. For example, the various combinations described below are suitable combinations

Reactor operations possible. Without wishing to be bound by any particular theory, the inventors consider that the HCl formed by hydrogenation of STC with hydrogen in all of these variants is the

Hydrochlorination reaction of the silicon contained in the solid deposits to chlorosilanes and in particular to hydrogen-containing chlorosilanes favored. This HCl is also the thermodynamic equilibrium of the

Hydrodehaiogenierung withdrawn from STC, so that in addition by the

resulting equilibrium shift increases the yield of hydrogen-containing chlorosilanes and in particular to TCS. In a specific embodiment of the process according to the invention, at least one, optionally each, reaction space is alternately a)

Organochlorosilane or methylthchlorosilane and b) the silicon tetrachloride in each case in admixture with the hydrogen for hydrogenation. The hydrogenation of STC on the one hand and MTCS on the other hand preferably takes place simultaneously in separate reaction spaces.

It is advantageous to use STC: MTCS (or OCS) in a molar ratio of 50: 1 to 1: 1, preferably from 20: 1 to 2: 1, and STC: H ₂ from 1: 1 to 8: 1, preferably from 2: 1 to 6: 1, and MTCS (or OCS): H ₂ from 1: 1 to 8: 1, preferably from 2: 1 to 6: 1.

The changes between the supply of STC on the one hand and MTCS or OCS on the other hand, in each case in admixture with the hydrogen, to the individual Reaction spaces can be carried out simultaneously for all reaction spaces or independently of each other. The times of change can be determined, in particular, as a function of changes in the pressure and / or material balance measured in at least one reaction space. These parameters may be suitable for indicating the formation of a significant amount of solid deposits, or conversely, the substantial degradation of formed solid deposits in the reactor. Thus, solid deposits in a reaction space can reduce its flow cross-section and thus cause a pressure drop. The pressure measurement can be carried out by any methods known in the art, e.g. B. by means of suitable mechanical, capacitive, inductive or piezoresistive pressure gauges. Substantial degradation of Si-based

Solid deposits in a reaction space can, for. Example, at an increased HCl concentration in the product gas mixture leaving this reaction space, be apparent, since the consumption of HCl is reduced by the Hydrochlorierungsreaktion with silicon due to the decreasing availability of the latter. The composition of the product gas may be analyzed by known analytical techniques, e.g. B. be measured by gas chromatography in combination with mass spectrometry. The change of the feed of the educts to the individual reaction chambers in the manner described above can be carried out by means of a suitable conventional control valve system.

The molar ratio of H ₂ to MTCS is typically adjusted to be in the range of 1: 1 to 8: 1, preferably 2: 1 to 6: 1, as the reactants are fed to the reaction spaces in this reactor mode molar ratio of H ₂ to STC is usually set in a range of 1: 1 to 8: 1, preferably 2: 1 to 6: 1. In a preferred operating mode of the reactor according to the invention, the methyltrichlorosilane and the silicon tetrachloride are simultaneously fed to at least one common reaction space in a mixture with the hydrogen for hydrogenation, the molar ratio of methyltrichlorosilane to Silicon tetrachloride in a range of 1:50 to 1: 1, the molar ratio of methyltrichlorosilane to hydrogen in a range of 1: 1 to 8: 1 and the molar ratio of silicon tetrachloride to hydrogen in a range of 1: 1 to 8: 1 set becomes. In the simplest case, the reaction thus takes place in a single common reaction space. By permanently decomposing the Si deposited in the reaction of MTCS by the HCl formed at the same time in the same reaction space in the hydrodehalogenation of STC, a permanently stable operation is maintained. In a further preferred reactor operation of the process according to the invention, the silicon tetrachloride in admixture with the hydrogen is fed to at least one first reaction space and the methyltrichlorosilane, optionally in admixture with the hydrogen, to at least one second reaction space for hydrogenation, the product gas mixture leaving the at least one first reaction space being at least a second reaction space is additionally supplied. Intermediate in the hydrogenation of MTCS in the at least one second reaction space deposited silicon can be degraded in the sequence by the HCI-containing product gas mixture from the at least one first reaction space again and the operation of the hydrogenation reactor in this way permanently stable upright.

The hydrogen needed for the reactions can be found in the above

Reaktorverschaltung are also supplied exclusively together with STC the reactor via the at least one first reaction space. The at least one second reaction space can then with an MTCS stream to the

Product gas mixture is supplied from the at least one first reaction space fed. Hydrogen contained in said product gas mixture and unreacted in the at least one first reaction space can then react with MTCS in the at least one second reaction space. However, it is preferred that hydrogen is supplied to the reactor both together with STC, feeding the at least one first reaction space, as well as together with MTCS, feeding the at least one second reaction space. This allows a more independent setting of advantageous molar ratios for the hydrodehalogenation of STC in the first reaction space and for the

Hydrogenation of MTCS in the second reaction space.

The molar ratio of H ₂ to STC for the reaction in the at least one first reaction space is preferably set in a range from 1: 1 to 8: 1, preferably 2: 1 to 6: 1. The molar ratio of hydrogen to MTCS is preferably set in the reaction in the at least one second reaction space to be in the range from 1: 1 to 8: 1, preferably 2: 1 to 6: 1.

All variants of the process according to the invention have in common that the hydrogenation in the hydrogenation reactor typically at a pressure of 1 to 10 bar, preferably from 3 to 8 bar, more preferably from 4 to 6 bar, a temperature greater than 800 ° C, preferably at a temperature in the range of 850 ° C to 950 ° C, and gas streams having a residence time in the range of 0.1 to 10 s, preferably from 1 to 5 s,

is carried out.

The product gas mixture formed in the process according to the invention by the hydrogenation of STC and MTCS with H ₂ typically comprises at least HCl and methane in addition to at least one hydrogen-containing chlorosilane. In addition to oligomeric and monomeric chlorosilanes, in particular hydrogen-containing

Chlorosilanes, z. SiH ₄ , SiCl ₃ , SiCl ₂ H ₂ (DCS), STC and TCS, organochlorosilanes such as MTCS, MHDCS and dimethyldichlorosilane. As a volatile component, in addition to HCl, CH ₄ unreacted hydrogen in the

Product gas mixture may be present. In the case of boron contamination, various chlorinated boron compounds may also be included in the product gas mixture. As components, the product gas mixture comprising the reaction of STC and MTCS with hydrogen in the hydrogenation reactor typically comprises at least three or all products from the group comprising HCl, methane, hydrogen,

Dichlorosilane, trichlorosilane, silicon tetrachloride, methyldichlorosilane and

Methyltrichlorosilane. Frequently, the product gas mixture also contains high boilers. The components contained in the product gas mixture are usually isolated in the sequence as pure as possible and then their further

Use, preferably supplied within the composite process. The workup of the product gas mixture may vary depending on the composition of the product gas mixture and must meet the requirements of the respective process and composite process. Suitable embodiments and apparatuses of usable physical-chemical separation processes, such as

Condensation, freezing, distillation, absorption and / or adsorption may, for. B. Ullmann's Encyclopedia of Industrial Chemistry, 4th ed., Verlag Chemie GmbH, Weinheim, Volume 2, page 489 ff. Are removed. Specific

Embodiment variants that can be used in the composite method according to the invention are described below. At least part of at least one separated by the work-up

Product is used as a reactant of hydrogenation or as a starting material of another process within the composite process.

Thus, in the hydrogenation unreacted starting materials can advantageously be attributed to the hydrogenation reactor. Hydrogen obtained by working up the product gas mixture is thus typically at least partially used as starting material for the hydrogenation in the composite process according to the invention. Likewise obtained by workup of the product gas mixture obtained silicon tetrachloride and / or methyltrichlorosilane are usually at least partially used as reactants of the hydrogenation.

HCl obtained by working up the product gas mixture may be used at least partially as a starting material in a process for the hydrochlorination of Si within the composite process, as long as a process for the hydrochlorination of Si is part of the composite process. In this case also from the

Product gas mixture separated high boilers use at least partially as reactants for the hydrochlorination of Si within the composite process. About that In addition, these can be taken from the composite process at least partially as products for re-use or disposal.

Trichlorosilane obtained by working up the product gas mixture may be used, at least in part, as a starting material in a process for depositing silicon from the gaseous phase within the composite process, provided that a process for depositing silicon from the gaseous phase is part of the

Composite method is, and / or the composite method at least partially taken as a product for further use. Thus, that allows

Composite method, a significant increase in the yield of the commercially valuable product TCS, with the above-mentioned further use of TCS in the composite process for the production of hyperpure silicon for semiconductor and photovoltaic applications is particularly preferred. Dichlorosilane, which by working up the product gas mixture in

The inventive method may optionally be obtained in admixture with TCS, the composite method is preferably at least partially as a product

Further use taken. For example, downstream can be a

Functionalization with organic radicals by hydrosilylation

be made. Also obtained by working up the product gas mixture of the hydrogenation methyldichlorosilane is the composite process

usually at least partially as a product for re-use outside the composite process, e.g. B. as starting material and / or additive in various

Follow-up processes, taken.

In addition, methane obtained by working up the product gas mixture can advantageously be used, at least in part, as fuel for heating the hydrogenation reactor. For this purpose, the separated methane-containing gas in the composite process according to the invention at least one burner, which is directed into the heating chamber, in which the reaction chambers of the hydrogenation reactor are arranged, fed and burned with the addition of air or oxygen. The invention further relates to a composite system for carrying out a process for producing a product gas mixture containing at least one hydrogen-containing chlorosilane by working up the product gas mixture by separating at least one part of at least one product and using at least one part of at least one of the optionally separated products in the process, characterized in that the composite system comprises:

- a unit for the hydrochlorination of silicon and / or a unit for the separation of silicon from the gas phase,

- a unit for the implementation of a Müller-Rochow synthesis,

- A hydrogenation reactor for the hydrogenation of at least

Silicon tetrachloride and methyltrichlorosilane,

a unit for working up a product gas mixture formed in the hydrogenation reactor,

and one or more of the following components:

a line for feeding methane obtained by working up the product gas mixture to at least one burner for heating the hydrogenation reactor,

a line for supplying hydrogen obtained by working up the product gas mixture to the hydrogenation reactor,

a line for feeding methyltrichlorosilane and / or silicon tetrachloride obtained by working up the product gas mixture to the hydrogenation reactor,

a conduit for supplying HCl obtained by the work-up of the product gas mixture and / or obtained

High boilers to the hydrochlorination unit of silicon,

a conduit for feeding trichlorosilane obtained by the work-up of the product gas mixture to the sub-plant for the deposition of silicon from the gas phase,

- a line for the removal of by the processing of the

Product gas mixture obtained dichlorosilane and / or trichlorosilane,

a conduit for the removal of methyldichlorosilane obtained by working up the product gas mixture, - a line for the removal of by the processing of the

Product gas mixture obtained high boiler.

This composite system, as illustrated by way of example in FIG. 1, preferably serves for carrying out the composite method according to the invention. When operating the unit for the hydrochlorination of silicon and / or the subsystem of

Deposition of silicon from the gas phase typically falls here

Silicon tetrachloride as a by-product, while MTCS is formed as a by-product during operation of the unit to perform a Müller-Rochow synthesis. These STC-containing side streams and MTCS-containing secondary streams can be collected in each case in a reservoir and from there to the hydrogenation reactor for

Implementation can be supplied with additionally fed hydrogen.

The workup of the product gas mixture formed in the hydrogenation reactor can be carried out as previously stated according to methods known per se in the prior art. Thus, specific embodiments described below are to be considered as exemplary only and not as limiting.

Thus, hydrogen in a particular embodiment of the process according to the invention in the workup of the product gas mixture is typically

separated by at least the steps:

Cooling the product gas mixture,

Contact of the non-condensed and H ₂ -containing portion of

Product gas mixture with an absorption medium,

Contact of the unabsorbed parts with an organic one

Compounds adsorbing adsorption medium, and removal of the unadsorbed hydrogen. Similarly, methane can be separated in the workup of the product gas mixture by at least the steps:

Cooling the product gas mixture, Contact of the non-condensed and CH ₄ -containing portion of

Product gas mixture with an absorption medium,

Contacting the unabsorbed fractions with a CH ₄ adsorbent adsorbent medium, and

Desorption of the adsorbed methane and removal.

By cooling the product gas mixture of the hydrogenation, which initially contains at least several of the components H ₂ , HCl, CH, DCS, TCS, STC, MHDCS, MTCS and high boilers, to temperatures less than -70 ° C, the volatile constituents contained therein of the condensing Components are separated.

The absorption medium with which the uncondensed portion of

Product gas mixture is then contacted, preferably comprises at least one chlorosilane. The contact with the absorption medium can be carried out in such a way that the gas mixture is passed over a fluidized bed. HCl and chlorosilanes contained in the gas mixture can thus be removed by absorption. The gas stream leaving the absorption unit then contains H ₂ , CH ₄ and other exhaust gases and can subsequently be passed through a suitable adsorption medium for adsorptive separation. As adsorption medium is suitable

in particular activated carbon. Methane and other exhaust gases are adsorbed by the activated carbon, while the hydrogen is not adsorbed by this adsorption medium and thus in a purified form from contact with

Activated carbon can be obtained. After at least partial saturation of the

Adsorption medium with CH ₄ and other exhaust gases, however, the adsorbates can be released gaseous by desorption and fed in the sequence of their further use. The desorption can be carried out, for example, thermally by heating the adsorption medium. The CH ₄ -containing exhaust gas stream is preferably fed to a burner for energy and heat generation. The condensate from the cooling of the original product gas mixture of the hydrogenation to temperatures below -70 ° C, which contains one or more of the components HCl, DCS, TCS, STC, MHDCS, MTCS and high boilers, is typically used for the separation of a subsequent distillation

Workup subjected. If an absorption medium comprising at least one chlorosilane for contacting the non-condensed portion of

Product gas mixture is used, this is preferably combined after the absorption step with the condensate for distillative work-up. For example, during the workup of the product gas mixture, HCl can be separated off by at least the steps:

Cooling the product gas mixture,

Pressure distillation of the condensate, optionally combined with the

Absorption medium after its contact with the uncondensed

Proportion of product gas mixture, and

Removal of the HCl via the top of the pressure distillation column.

The Si-based compounds and high-boiling compounds, however, are in the

Workup of the product gas mixture typically separated by at least the steps:

Cooling the product gas mixture,

Pressure distillation of the condensate, optionally combined with a

Absorption medium after its contact with the uncondensed

Proportion of product gas mixture, and

Multi-stage distillation of the distillation residue from the pressure distillation. Thus, high boilers can be separated here as a residue of the first distillation stage. In a preferred variant of the invention, the multi-stage distillation of the distillation residue of the pressure distillation may be four or more

Include distillation stages. A mixture comprising silicon tetrachloride and methyltrichlorosilane can in this case as a residue of the second

Distillation column and a mixture comprising dichlorosilane and trichlorosilane are separated via the top of the third distillation column. Further, in this way, a mixture containing methyldichlorosilane as a residue of the fourth

Distillation column to be separated. In particular, however, trichlorosilane can thus be separated off via the top of the fourth distillation column. Trichlorosilane separated in this way from the product mixture of the hydrogenation reactor can be used for the separation of silicon from the gas phase in the absence of further work-up

Compound method according to the invention can be used.

The unit for working up the hydrogenation formed in the hydrogenation reactor

Product gas mixture in the composite system may thus comprise one or more of the following components:

a unit for cooling the product gas mixture transferred from the hydrogenation reactor to a temperature <-70 ° C.,

a unit for contacting the non - condensed fraction of

Product gas mixture with an absorption medium, preferably an absorption medium comprising at least one chlorosilane,

a unit for contacting the unabsorbed components of the

Product gas mixture an adsorption medium, preferably activated carbon,

a unit for the pressure distillation of the condensate,

- A unit for the multi-stage distillation of the residue of pressure distillation. A special suitable embodiment of the subsystem for processing the

Product gas mixture comprising all of the above components and in which the multi-stage distillation of the residue of the pressure distillation as above described in four series-connected distillation columns, is exemplified in Fig. 2.

FIG. 1 shows by way of example and schematically a composite system according to the invention.

FIG. 2 shows, by way of example and schematically, a possible variant of a unit for working up the product gas mixture, which after hydrogenation of STC and MTCS with hydrogen in the hydrogenation reactor according to the invention

Procedure is obtained.

The composite system 1 shown in Figure 1 comprises a subsystem 2 to

Hydrochlorination of silicon and a sub-unit 3 for the deposition of silicon from the gas phase, wherein obtained during their operation silicon tetrachloride-containing side streams are fed via a line 4 to a reservoir 5 for collection. Furthermore, the composite system comprises a subsystem 6 for

Implementation of a Müller-Rochow synthesis during their operation

incurred methyltrichlorosilane side streams, which are passed via a line 7 in a reservoir 8 and collected there. The sidestreams containing the STC and the MTCS-containing sidestreams are fed from their reservoirs via one or possibly a plurality of line (s) 9 with the addition of hydrogen via one or optionally a plurality of further line (s) 10 to the hydrogenation reactor 11 for hydrogenation. The resulting product gas mixture is transferred via a line 12 from the hydrogenation reactor to a unit 13 for working up the product gas mixture in which a material separation of the product gas mixture takes place. Via lines 14, 15, STC and MTCS or H ₂ separated off from the workup of the product gas mixture are fed to the hydrogenation reactor for reuse as starting materials.

Methane-containing exhaust gas from the workup of the product gas mixture can be fed via a line 16 to at least one burner for heating the hydrogenation reactor. Separated HCl and a part of the isolated high boiler are fed via a line 17 in the unit 2 for the hydrochlorination of silicon as starting materials during the essential part of the trichlorosilane obtained by the work-up of the product gas mixture of the hydrogenation via another line 18 of the unit 3 for the deposition of silicon from the gas phase as Feedstock is supplied. Further lines 19, 20, 21 can also be used to separate the composite system 1 in each case by working up the product gas mixture

DCS / TCS mixture, methyldichlorosilane-containing mixture or high boiler are taken and fed to another use outside the composite process.

The partial system 13 shown in FIG. 2 for working up the product gas mixture comprises a cooling unit 22, in which the product gas mixture fed from the hydrogenation reactor 11 via a line 12 for the condensation of the non-volatile

Components is cooled. The non-condensed constituents of

Product gas mixture are fed via a line 23 of an absorption unit 24 and fed there with a via another line 25

Absorption medium comprising at least one chlorosilane brought into contact. Via further line 26, the portions of the gas mixture not absorbed by the absorption medium are fed to a downstream adsorption unit 27 where they are brought into contact with activated carbon as the adsorption medium. The

Methane-containing adsorbate can be desorbed after at least partial saturation of the activated carbon and via a corresponding line 16 from the unit to

Workup of the product gas mixture 13 are removed while hydrogen is not adsorbed by the activated carbon and the outlet of the adsorption 27 can be removed directly via another line 15. The condensate removed from the cooling unit 22 is fed via a line 28 with the absorption medium comprising at least one chlorosilane from the

Absorption unit after its contact with the non-condensed constituents of the product gas mixture by means of a further line 29 a

Pressure distillation unit 30 supplied. HCl can be over the head of the

Subtracted pressure distillation column and fed via a connected line 17 to a further use. The residue of the pressure distillation, however, is transferred by means of a further line 31 to a downstream unit for multistage distillation 32, wherein he herein a first

Distillation column 33 is supplied. About a line 17,21 is the

Distillation residue of the first distillation column 33 containing high boiler, taken. The top stream of the first distillation column 33, however, over a line 34 is transferred to a second distillation column 35. The second distillation column 35 can be removed via a further line 14, a STC and MTCS-containing mixture as the distillation residue. The top stream of the second distillation column 35 is in turn transferred 36 to a third series-connected distillation column 37. The top stream of this third

Distillation column 37 containing a mixture of DCS and TCS is discharged via a further line 19 for further use during the

Distillation residue by means of another line 38 to a fourth

Destillation column 39 is transferred. As the distillation residue of this fourth distillation column 39, a MHDCS-containing mixture is then removed via a corresponding line 20 while TCS can be taken off at the top of the fourth distillation column 39 and fed via another line 18 to its further use.

LIST OF REFERENCE NUMBERS

(1) composite system

(2) Subsystem for Hydrochlorination of Silicon

(3) Unit for the deposition of silicon from the gas phase

(4) Line for STC-containing secondary streams

(5) Reservoir for STC-containing secondary streams

(6) Unit for the implementation of a Müller-Rochow synthesis

(7) Line for MTCS-containing secondary streams

(8) Reservoir for MTCS-containing secondary streams

(9) feedstock (s) to the hydrogenation reactor

(10) line (s) for H ₂

(1 1) Hydrogenation reactor

(12) line for the product gas mixture of hydrogenation

(13) Unit for processing the product gas mixture

(14) Line (s) for STC and / or MTCS separated from the product gas mixture

(15) Line for separated from the product gas mixture H ₂

(16) Line for separated from the product gas mixture CH ₄

(17) line (s) for separated from the product gas mixture HCl and / or high boiler

(18) Line for separated from the product gas mixture TCS

(19) Line (s) for separated from the product gas mixture DCS and / or TCS

(20) Line for MHDCS separated from the product gas mixture

(21) Line for separated from the product gas mixture high boiler

(22) Cooling unit

(23) Uncondensed component line of the product gas mixture

(24) Absorption unit

(25) Supply line for absorption medium

(26) Conduction for unabsorbed by absorption medium fractions of

gas mixture

(27) adsorption unit (28) condensed component line of the product gas mixture

(29) Absorbent media line after contact with uncondensed components of the product gas mixture

(30) Pressure distillation unit

(31) Line for transferring the residue of pressure distillation

(32) Unit for multi-stage distillation

(33) First distillation column

(34) Line for transferring the overhead stream of the first distillation column

(35) Second distillation column

(36) Line for transferring the overhead stream of the second distillation column

(37) Third distillation column

(38) Line for transferring the residue of the third distillation column

(39) Fourth distillation column

Claims

A process for the preparation of a product gas mixture (12) comprising at least one hydrogen-containing chlorosilane within a

Composite process (1) by hydrogenation (1 1) of at least the reactants

Silicon tetrachloride (5, 14) and methyltrichlorosilane (8, 14) with hydrogen (10, 15) in a one or more reaction spaces

Hydrogenation reactor (1 1), wherein the method additionally comprises a work-up (13) of the product gas mixture (12) by separating at least one part

at least one product and the use of at least one part of at least one of the optionally separated several products as starting material (14, 15) of the hydrogenation (1 1) or as starting material (17, 18) of at least one other

Method (2,3,6) within the composite method (1),

characterized,

the hydrogenation reactor (11) is operated under pressure and the one or more reaction chambers each consist of a reactor tube of gas-tight ceramic material.

Method according to claim 1,

characterized,

that the product gas mixture (12) in addition to at least one

hydrogen-containing chlorosilane (14, 18, 19, 20) comprises at least HCl (17) and methane (16).

Method according to claim 1 or 2,

characterized,

the product gas mixture (12) comprises at least three or all products selected from the group consisting of HCl (17), methane (16), hydrogen (15), dichlorosilane (19), trichlorosilane (18, 19), silicon tetrachloride (14), methyldichlorosilane (20 ) and methyltrichlorosilane (14).

Method according to one of the preceding claims,

characterized, in that the at least one other process within the composite process (1) comprises at least one process selected from the group comprising a process for the hydrochlorination of silicon (2), a process for

Deposition of silicon from the gas phase (3) and a method for

Performing a Muller-Rochow synthesis (6).

Method according to claim 4,

characterized,

in that at least a part of the STC (5) and / or MTCS (8) used as starting material of the hydrogenation (1 1) is by-product of at least one of the others

Method (2,3,6).

Method according to one of the preceding claims,

characterized,

in that HCl (17) obtained by the work-up (13) of the product gas mixture (12) is at least partly used as starting material in the process (2) for the hydrochlorination of Si within the composite process (1).

7. Method according to one of the preceding claims,

characterized,

that silicon tetrachloride and / or methyltrichlorosilane obtained by work-up (13) of the product gas mixture (12) are used at least partly as educts (14) of the hydrogenation (11).

Method according to one of the preceding claims,

characterized,

that hydrogen (15) obtained by the work-up (13) of the product gas mixture (12) is used at least partially as the educt of the hydrogenation (11).

Method according to one of the preceding claims,

characterized, that methane (16) obtained by the work-up (13) of the product gas mixture (12) is at least partially used as fuel for heating the

Hydrogenation reactor (1 1) is used. 10. The method according to any one of the preceding claims,

characterized,

in that trichlorosilane obtained by the work-up (13) of the product gas mixture (12) is at least partially used as educt (18) in the process (3) for the deposition of silicon from the gas phase within the

Composite method (1) is used and / or the composite method (1) is at least partially taken as a product (19) for further use.

1 1. Method according to one of the preceding claims,

characterized,

that obtained by the workup (13) of the product gas mixture (12)

High boilers are at least partially used as starting materials (17) in the process (2) for the hydrochlorination of Si within the composite process (1) and / or the composite process (1) are taken at least partially as products (21) for further use.

12. The method according to any one of the preceding claims,

characterized,

that dichlorosilane obtained by the workup (13) of the product gas mixture (12) is at least partially taken from the composite process (1) as a product (19) for further use.

13. Method according to one of the preceding claims,

characterized,

that obtained by the workup (13) of the product gas mixture (12) methyldichlorosilane the composite process (1) at least partially as a product

(20) for further use.

14. The method according to any one of the preceding claims,

characterized,

that in the work-up (13) of the product gas mixture (12) hydrogen (15) is separated by at least the steps:

Cooling (22) the product gas mixture (12),

- contact of the non-condensed and H ₂ -containing fraction (23) of the

Product gas mixture (12) with an absorption medium (25),

- Contact (27) of the unabsorbed portions (26) with an organic

Compounds (16) adsorbent adsorption medium, and

- Removal of the unadsorbed hydrogen (15).

15. The method according to any one of the preceding claims,

characterized,

that during work-up (13) of the product gas mixture (12), methane (16) is separated off by at least the steps:

Cooling (22) the product gas mixture (12),

Contact of the non - condensed and CH ₄ containing fraction (23) of the

Product gas mixture (12) with an absorption medium (25),

Contacting (27) the unabsorbed portions (26) with a CH ₄ adsorbing adsorption medium, and

- desorption of adsorbed methane and removal (16).

16. The method according to any one of the preceding claims,

characterized,

that in the workup (13) of the product gas mixture (12) HCl (17) is separated by at least the steps:

Cooling (22) the product gas mixture (12),

- Pressure distillation (30) of the condensate (28), optionally combined with the

Absorption medium (25) after its contact with the non-condensed portion (23) of the product gas mixture (12), and

- Removal of the HCl (17) via the top of the pressure distillation column.

17. The method according to any one of the preceding claims,

characterized,

that in the workup (13) of the product gas mixture (12) Si-containing

Compounds (14, 18, 19, 20) and high boilers (17, 21) are separated by at least the steps:

Cooling (22) the product gas mixture (12),

- Pressure distillation (30) of the condensate (28), optionally combined with a

- multi - stage distillation (32) of the distillation residue (31)

Pressure distillation (30).

18. The method according to claim 17,

characterized,

that the high-boiling components (17, 21) are separated off as the residue of the first distillation stage (33).

19. The method according to claim 17,

characterized,

in that the multistage distillation (32) of the distillation residue (31) of the pressure distillation (30) comprises four or more distillation stages (33, 35, 37, 39).

20. Composite system (1) for carrying out a method for producing a product gas mixture (12) comprising at least one hydrogen-containing chlorosilane while working up (13) of the product gas mixture (12)

Separation of at least a portion of at least one product and

Use at least part of at least one of the optionally separated products in the process,

characterized,

the composite system (1) comprises:

- A unit (2) for the hydrochlorination of silicon (2) and / or a

Subsystem (3) for the deposition of silicon from the gas phase,

a unit (6) for carrying out a Müller-Rochow synthesis, - A hydrogenation reactor (1 1) for the hydrogenation of at least

Silicon tetrachloride and methyltrichlorosilane

a subsystem (13) for working up a product gas mixture (12) formed in the hydrogenation reactor,

and one or more of the following components:

- A line (16) for supplying by the workup (13) of the

Product gas mixture (12) obtained methane to at least one burner for heating the hydrogenation reactor (1 1),

- A conduit (15) for supplying by the workup (13) of the

Product gas mixture (12) received hydrogen to the hydrogenation reactor

(1 1),

- A line (14) for supplying by the workup (13) of the

Product gas mixture (12) obtained methyltrichlorosilane and / or

Silicon tetrachloride to the hydrogenation reactor (1 1),

- A line (17) for supplying by the workup (13) of the

Product gas mixture (12) obtained HCl and / or obtained

High boilers to the unit (2) for the hydrochlorination of silicon,

- A line (18) for supplying by the workup (13) of the

Product gas mixture (12) received trichlorosilane to the sub-unit (3) for the deposition of silicon from the gas phase,

- A line (19) for removal by the workup (13) of the

Product gas mixture (12) obtained dichlorosilane and / or trichlorosilane,

- A line (20) for the removal of by the workup (13) of the

Product gas mixture (12) of methyldichlorosilane obtained,

- A line (21) for the removal of by the workup (13) of the

Product gas mixture (12) obtained high boiler.

Composite system according to claim 20,

characterized,

in that the unit (13) for working up the product gas mixture (12) formed in the hydrogenation reactor comprises one or more of the following components: - A unit (22) for cooling the from the hydrogenation reactor (1 1)

transferred product gas mixture (12) to a temperature <-70 ° C,

a unit (24) for contacting the non-condensed portion (23) of the product gas mixture (12) with an absorption medium (25),

a unit (27) for contacting the unabsorbed portions (26) of the

Product gas mixture (12) with an adsorption medium,

a unit (30) for pressure distillation of the condensate (28)

a unit (32) for the multistage distillation of the residue of

Pressure distillation.