Patent Application
20110229398
The present invention relates to an apparatus, the use thereof and a process for substantially energy-independent continuous preparation of chlorosilanes, in particular for the preparation of trichlorosilane as an intermediate for obtaining high-purity silicon.
Trichlorosilane, in particular in pure form, is now an important starting material inter alia for the production of high-purity silicon, for example for the production of chips or solar cells (WO 02/48034, EP 0 921 098).
Unfortunately, the known processes are complicated and energy-intensive. Thus, attempts have been made to prepare the material more and more economically in spite of very high quality requirements.
It has long been known that chlorosilanes can be prepared in a fluid bed or fluidized bed reactor from metallurgical silicon (Si) with addition of hydrogen chloride (HCl) or methyl chloride (inter alia U.S. Pat. No. 4,281,149).
The reaction of silicon with HCl is highly exothermic. As a rule, trichlorosilane (TCS) and silicon tetrachloride (STC) are obtained as main products. Furthermore, the use of special materials for producing the reactor should be taken into account (DE 36 40 172).
Attention is also being paid to the selectivity of the reactions. Thus, the reactions can be influenced by the presence of more or less suitable catalysts. Inter alia, Fe, Cr, Ni, Co, Mn, W, Mo, V, P, As, Sb, Bi, O, S, Se, Te, Ti, Zr, C, Ge, Sn, Pb, Cu, Zn, Cd, Mg, Ca, Sr, Ba, B, Al, Y, Cl are mentioned in the literature as examples of these. As a rule, such catalysts are already present in the metallurgical silicon, for example in oxidic or metallic form, as silicides or in other metallurgical phases. Moreover, catalysts may be added or may be present in said reactions in metallic or alloyed or salt-like form. Thus, the wall or surface material of the reactor used can also have a catalytic influence in the reaction (inter alia B. Kanner and K. M. Lewis “Commercial Production of Silanes by the direct Synthesis”, pages 1-66, Studies in Organic Chemistry 49, Catalyzed Direct Reactions of Silicon, edited by K. M. Lewis and D. G. Rethwisch, 1993, Elsevier Science Publishers; H. Samori et al., “Effects of trace elements in metallurgical silicon on trichlorosilane synthesis reaction”, Silicon for the chemical industry III, Sandefjord, Norway, Jun. 18-20, 1996, pages 157-167; J. Acker et al., “Formation of silicides in the system Metal-Silicon-Chlorine-Hydrogen: Consequences for the synthesis of trichlorosilane from silicon an hydrogen chloride”, Silicon for the chemical industry, Tromso, Norway, May 29-Jun. 2, 2000, pages 121-133; W. C. Breneman et al., “A comparison of the Trichlorosilane and silane routes in the purification of metallurgical grade silicon to semiconductor quality”, Silicon for the chemical industry IV, Geiranger, Norway, Jun. 3-5, 1998, pages 101-112; WO 03/018207, WO 05/003030).
Another possibility for the preparation of trichlorosilane is the thermal conversion of silicon tetrachloride and hydrogen in the gas phase in the presence or absence of a catalyst. This synthesis route is likewise very energy-intensive since the reaction takes place endothermically (DE 10 2006 050 329, DE 10 2005 046703).
It is also possible to react metallurgical silicon with silicon tetrachloride and hydrogen (DE 33 11 650) or silicon with silicon tetrachloride, hydrogen and HCl (DE 100 63 863, DE 100 44 795, DE 100 44 794, DE 100 45 367, DE 100 48 794, DE 100 61 682). The reactions are carried out as a rule under pressure and at high temperature. Furthermore, these processes too require the supply of energy, which as a rule is effected electrically and is increasingly becoming a cost factor. Silicon, silicon tetrachloride and hydrogen or silicon, silicon tetrachloride, hydrogen and hydrogen chloride as starting components have to be metered into the reactor under reaction conditions of from 20 to 42 bar and from 400 to 800° C. and the reaction has to be started and kept running.
In the case of an interruption of operation, it is also necessary to keep the starting materials or starting material feed at the required operating pressure and temperature in standby operation in order to be able to start up again or to continue operation without long heating up times.
Thus, it was an object to provide a further, very economical possibility for the industrial, continuous reaction of silicon (Si), silicon tetrachloride (STC, SiCl4), hydrogen (H2) and optionally hydrogen chloride (HCl) and if desired further components in order to alleviate the abovementioned problems.
A particular concern of the present invention was to provide trichlorosilane (TCS, HSiCl3) in as energy-saving and economical manner as possible for an integrated system for the preparation of high-purity silicon, chloro- or organosilanes and organosiloxanes and pyrogenic silica.
This object is achieved, according to the invention, in accordance with the information in the patent claims.
Thus, it was surprisingly found that the reaction of particulate Si, chlorosilanes, in particular SiCl4, and H2 and optionally in the presence of at least one catalyst at a pressure of from 25 to 55 bar and a temperature from 450 to 650° C. can be carried out in a particularly energy-saving and hence economical manner if gas-fired burners, in particular natural gas burners, are used for heating the STC stream and the start-up process of the reactor and regulation or control when carrying out the present process.
Thus, particularly in the case of hydrogenation of SiCl4 in the present process, the necessary reaction energy can advantageously be supplied in a simple and particularly economical manner via the reactor heating.
In addition, by targeted introduction of HCl and/or Cl2 gas, it is possible to carry out the reaction or present conversion exothermally. Furthermore, excess quantity of heat can be removed via the reactor thermostatting and, by means of heat exchangers, advantageously used, for example, for preheating the starting material gases. Thus, HCl and/or Cl2 can be introduced or metered in a targeted manner into the fluidized bed reactor in order to regulate energy input for the start-up or for maintaining the present conversion or reactions in an advantageous energy-saving manner.
When carrying out the present process, at least one catalyst can also advantageously be used. A catalyst system based on at least one transition metal element, is preferably chosen, particularly preferably at least one metal from the series consisting of Fe, Co, Ni, Cu, Ta, W, for example in the form of the chlorides, such as FeCl2, CuCl, CuCl2, etc., and/or corresponding metal silicides or mixtures thereof, particularly preferably a copper-containing catalyst system.
Furthermore, the present process and the plant developed for this purpose, in particular the novel fluidized bed plant, and such a plant advantageously incorporated into so-called integrated systems for the preparation of chlorosilanes, silanes, organosilanes, organosiloxanes, pyrogenic and precipitated silica and solar silicon can particularly advantageously be carried out or operated industrially in a particularly economical, continuous procedure.
The present invention therefore relates to a fluidized bed reactor for the continuous hydrogenation of higher chlorosilanes of the formula HnSiCl4-n where n=0, 1, 2 or 3 in the presence of silicon, in particular for the preparation of chlorosilanes by reacting substantially silicon (A), silicon tetrachloride (B), hydrogen (C) and optionally hydrogen chloride gas and/or chlorine gas (D) and optionally in the presence of a catalyst at a pressure of from 25 to 55 bar and a temperature of from 450 to 650° C., the fluidized bed reactor unit (1) being based on
The waste heat from the units (1.2) and (1.3), transported via the pipes (1.14) to the heat exchanger (1.10) (so-called hot-gas recuperator), can advantageously be used, for example, for preheating gas streams (F) and/or, by means of heat exchanger (1.5.5), for preheating (C) and/or (D) containing gas streams. Thus, the waste heat of the plant units can advantageously additionally be used in a particularly energy-efficient manner for starting the reaction and maintaining and controlling it in the fluidized bed reactor according to the invention.
A reactor casing (1.1) having an internal diameter of from 100 mm to 2000 mm and a height of from 5 m to 25 m, particularly from 200 mm to 1500 mm internal diameter and a height of from 10 m to 20 m, is preferred there.
For start-up and uniform supply of a fluidized bed reactor unit (1) according to the invention with a heated starting material stream (B*), in particular STC, it is advantageous to use a (natural) gas-fired heater unit having a circulation (2) (cf. for example
The chlorosilane heater for start-up and supply of the fluidized bed unit (1) or (1.4) with chlorosilane (B*), in particular with an STC-containing chlorosilane stream, can, however, also be designed or implemented as described in the still unpublished parallel application PCT/EP2008/053079 with the title “Method for the gradual temperature control of chemical substances with defined input and output temperatures in a heater and device for carrying out said method”.
The fluidized bed reactor (1) or (1.1) is advantageously supplied via a fluidizing base for feeding in (B or B*) (1.4), the fluidized bed being started up via the volume flow and the height of fill of components (A) in the reactor (1.1) and the average residence time of the gaseous product mixture in the reactor being substantially regulated. The fluid dynamics in the reactor (1.1) can advantageously be additionally improved by the use of at least one sieve tray in the region above the feed (1.4) in the reactor or a sieve tray system which may comprise beds and/or baffles.
A fluidized bed reactor (1) according to the invention is preferably equipped with at least one gas metering unit for H2 (C) (1.5.4) and HCl and/or chlorine gas (D) (1.5.2) for supplying the feeds (1.5).
A flammable gas (E), preferably natural gas, is suitably used for firing a heater, such as (2.2) or (1.11).
The waste heat from the combustion chamber unit (2.2), removed via (2.2.2), can advantageously be used advantageously for preheating gas streams (F) and/or, by means of heat exchangers (1.5.5), for preheating (C) and/or (D) containing gas streams.
Furthermore, a fluidized bed reactor (1) according to the invention can advantageously comprise a dust separation (1.7), the dust separation being substantially based on filtration for the chlorosilane-containing product mixture obtained in the fluidized bed reactor and removed at the top of the reactor.
For separating the product mixture into the material streams (G) and (H), a separation unit (1.8) is to be provided in a suitable manner in the fluidized bed reactor (1) according to the invention, the material stream (H) being obtained as condensate and the material stream (G) being removed in gaseous form. Uncondensed chlorosilanes can advantageously be recycled together with the hydrogen into the (hydrogenation) reactor (1.1).
The plant parts of the fluidized bed reactor according to the invention (cf. inter alia
The present invention also relates to a process for the industrial continuous preparation of a trichlorosilane (TCS)-containing product stream by reacting substantially silicon (Si) (A), chlorosilanes, in particular silicon tetrachloride (STC), (B) and hydrogen (H2) (C) and optionally hydrogen chloride gas (HCl) and/or chlorine gas (Cl2) or a mixture of hydrogen chloride and chlorine gas (D) at a pressure of from 25 to 55 bar and a temperature of from 450 to 650° C., preferably from 35 to 45 bar and from 550 to 620° C., in particular from 38 to 42 bar and from 580 to 610° C., and optionally in the presence of at least one catalyst, preferably based on at least one transition metal element, particularly preferably at least one from the series consisting of Fe, Co, Ni, Cu, Ta, W, such as FeCl2, CuCl, CuCl2, and/or the corresponding metal silicides, in particular a copper-based catalyst system, by
In the process according to the invention, preferably from 1 to 5 mol of H2 (C), particularly preferably from 1.1 to 2 mol of H2, are used per mole of SiCl4 (B).
Particularly advantageously, from 0 to 1 mol of HCl (D), preferably from 0.001 to 0.7 mol of HCl, particularly preferably from 0.01 to 0.5 mol of HCl, very particularly preferably from 0.1 to 0.4 mol of HCl, in particular from 0.2 to 0.3 mol of HCl, is used for a procedure which is as energy-independent as possible in the process according to the invention.
Surprisingly, from 0 to 1 mol of Cl2 (D), preferably from 0.001 to 0.5 mol of Cl2, particularly preferably from 0.01 to 0.4 mol of Cl2, in particular from 0.1 to 0.3 mol of Cl2, per mole of H2 (C) can also advantageously be used for a procedure which is as energy-independent as possible.
A gas mixture comprising HCl and Cl2 in a molar ratio of HCl to Cl2 of from 0:1 to 1:0, preferably from 0.01:0.99 to 0.99:0.01, can also be suitably used as component (D).
In addition, an average residence time of the gas or vapor mixture in the reactor of from 0.1 to 120 seconds, preferably from 0.5 to 100 seconds, particularly preferably from 1 to 60 seconds, very particularly preferably from 3 to 30 seconds, in particular from 5 to 20 seconds, is advantageously ensured in the process according to the invention.
Compared with the process according to the invention, it was necessary to date according to the prior art, in the endothermic hydrogenation reaction of STC to give TCS, to supply the necessary quantity of energy to the reactor via electric heating.
Furthermore, it is advantageous if, in the process according to the invention, the reaction temperature for the reaction in the reactor interior is monitored and this is regulated at a constant hydrogen/STC ratio by the metering of HCl and/or Cl2 (D) and/or the reaction temperature for the reaction in the reactor (1.1) is controlled or additionally regulated via the units (1.2) and (1.3) with the use of the medium (F) and of the units (1.9) or (1.11). The quantity of heat to be supplied or removed can advantageously be regulated by the double jacket (1.2) and the internal heat exchanger unit (1.3) including the units (1.9) and (1.11). For example—but not exclusively—air or an inert gas, such as nitrogen, or a noble gas, such as argon, can be used as medium (F).
Furthermore, a—generally commercially available—metallurgical silicon having a mean particle size of from 10 to 3000 μm, preferably from 50 to 2000 μm, particularly preferably from 80 to 1500 μm, very particularly preferably from 100 to 1000 μm, in particular from 120 to 500 μm, is advantageously used as silicon (A) in the process according to the invention. The silicon (A) used here preferably has a purity greater than or equal to 80%, particularly preferably greater than or equal to 90%, in particular greater than or equal to 98%.
At least one catalyst can advantageously be mixed with the silicon (A) by thoroughly mixing the silicon and the catalyst system, in particular by milling the silicon and the catalyst together beforehand. For this purpose, milling methods known per se to the person skilled in the art can be used. In addition, dust (J) from the unit (1.7) can advantageously be recycled to the silicon or, in the case of the preparation of a mixture of silicon and catalyst, at least proportionately recycled.
As a rule, the process according to the invention is carried out as follows:
The reactor and the starting material- or product-transporting pipes of the plant are as a rule dried and rendered inert before the start of operation, for example by flushing the plant with a preheated inert gas, such as argon or nitrogen, until the proportion of oxygen tends to zero at the outlet.
For the start-up and subsequent uniform and continuous supply with a heated starting material stream (B*), a unit (2), i.e. a gas-fired chlorosilane heater having a circulation, is preferably connected upstream of the fluidized bed reactor (1) according to the invention, in which unit (2) the substantially STC-containing starting material stream (B) can be heated from about 20° C. to a temperature up to 650° C. and a pressure from to 55 bar and, in addition to control units and pressure-resistant pipes, the unit (2) is substantially based on a so-called feed pump (2.1) and on a gas-fired heat exchanger vessel (2.2) with gas burner (2.3) and expansion vessel with condensate recycling (2.4), the hot fumes in the combustion vessel flowing around at least one pressure-resistant pipe which serves for transporting the chlorosilane or STC stream (B). Furthermore, this unit comprises a suitable arrangement for a circulation procedure for uniform heating of the chlorosilane or STC stream (cf.
The present invention therefore also relates to the use of an apparatus according to the invention for the hydrogenation of higher chlorinated silanes of the formula HnSiCl4-n where n=0, 1, 2 or 3, preferably for the preparation of chlorosilanes of the formula HnSiCl4-n where n=1, 2, 3 or 4 which have a low degree of chlorination, in particular for the preparation of trichlorosilane.
Particularly advantageously, an apparatus according to the invention (also referred to below as fluidized bed stage for short) can be used in an integrated system for the preparation of chloro- or organosilanes, pyrogenic silica and/or high purity silicon for solar and electronic applications.
Thus, the present invention also relates to the use of an apparatus according to the invention (also referred to below as fluidized bed stage for short) in an integrated system for the preparation, known per se, of silanes and organosiloxanes, in particular chloro- or organosilanes, such as monosilane, monochlorosilane, dichlorosilane, trichlorosilane, silicon tetrachloride, vinyltrichlorosilane, substituted or unsubstituted C3-18-alkylchlorosilanes, such as 3-chloropropyltri-chlorosilane, propyltrichlorosilane, trimethoxysilane, triethoxysilane, tetramethoxysilane, tetraethoxysilane, vinyltrialkoxysilane, substituted or unsubstituted C3-18-alkylalkoxysilanes, such as propyltrialkoxy-silane, octyltrialkoxysilanes, hexadecyltrialkoxy-silane, chloroalkylalkoxysilanes, such as 3-chloro-propyltrialkoxysilane, fluoroalkylalkoxysilanes, such as tridecafluoro-1,1,2,2-tetrahydrooctyltrialkoxy-silane, aminoalkylalkoxysilanes, methacryloyloxyalkyl-alkoxysilanes, glycidyloxyalkylalkoxysilanes, poly-etheralkylalkoxysilanes, alkoxy being in each case, for example, methoxy and ethoxy, to mention but a few, and subsequent products thereof, chlorosilane streams, in particular STC-containing streams, being recycled at least proportionately into the process stages for the preparation of pyrogenic silica and for the preparation of chlorosilanes in the fluidized bed.
Trichlorosilane obtained in the fluidized bed stage according to the invention and subsequently purified is preferably used for the preparation of monosilane by dismutation, the silicon tetrachloride obtained in the dismutation being recycled at least proportionately into the monosilane process and/or it being fed at least proportionately to the STC heater of the fluidized bed reactor according to the invention. Monosilane thus obtained can advantageously be used for the preparation of polycrystalline silicon (solar grade) by thermal decomposition of monosilane. Furthermore, the hydrogen occurring in the thermal decomposition of the monosilane can advantageously be recycled into the fluidized bed stage according to the invention in the integrated system.
Thus, according to the invention, an apparatus and a substantially energy-independent process for the preparation of trichlorosilane starting from metallurgical silicon, silicon tetrachloride and hydrogen and optionally HCl and/or Cl2 and optionally in the presence of a catalyst can be provided and particularly advantageously used—as shown above—in a particularly economical manner with simultaneously high yield and with a gentle procedure for the material of the reactor.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 041 974.5 | Sep 2008 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/058790 | 7/10/2009 | WO | 00 | 5/31/2011 |
