WO2006098722A1

WO2006098722A1 - Process for the production of hydrochlorosilanes

Info

Publication number: WO2006098722A1
Application number: PCT/US2005/008204
Authority: WO
Inventors: William C. Breneman
Original assignee: Rec Advanced Silicon Materials Llc
Priority date: 2005-03-09
Filing date: 2005-03-09
Publication date: 2006-09-21
Also published as: CN101189245B; EP1861408A1; NO20076030L; TWI454424B; TW200704589A; CN101189245A; JP2008532907A; DE112005003497T5; KR101176088B1; JP4813545B2; KR20080008323A; EP1861408A4

Abstract

Hydrogen-containing chlorosilanes are prepared by reacting hydrogen with silicon tetrachloride and/or hydrogen chloride and silicon wherein the surface of the silicon has been modified by a chemical vapor deposition of one or more catalytic materials, such as copper.

Description

PROCESSFORTHEPRODUCTION OFHYDROCHLOROSILANES

Background and Summary

This invention concerns a process for the production of hydrogen-containing chlorosilanes, particularly trichlorosilane and dichlorosilane from silicon.

It is known to produce trichlorosilane by reaction of silicon tetrachloride with hydrogen and silicon without the use of a catalyst or promoter (Ingle, US 4526769). The overall course of the reaction is represented by:

3 SiCl₄ + 2 H₂ + Si ^ 4 HSiCl₃ (1)

It is also known that trichlorosilane can be prepared by the reaction of hydrogen chloride and silicon without a catalyst as represented by:

3 HCl + Si -> HSiCl₃ + H₂ (2)

It is also known that the rate of reaction and the selectivity of the reactions can be increased if certain metals, such as copper, are used (Breneman, US 4676967). The manner by which such a catalyst is incorporated into the process has been the subject of several publications. Furthermore, a catalyst is required to produce significant amounts of dichlorosilane by the reaction:

2 HCl + Si ^■* H₂SiCl₂ (3)

Wagner (US 2499009) used large amounts of copper halides in a staged roasting method to prepare a copper-silicon material useful for promoting the formation of dichlorosilane. However, the batch processing, final high temperature annealing, and the high concentration of copper required made his method impractical and posed severe environmental challenges for disposal of the waste that included the large amounts copper. Downing, (US 4314908) teaches a method whereby copper oxide was roasted with metallurgical grade silicon in a hydrogen atmosphere at an elevated temperature to produce a substantially uniform distribution of copper on the surface of the silicon. Mui (US 5250716) describes the formation of a copper-silicon alloy by reacting cuprous chloride vapor with silicon. Wakamatsu (DE 19654154) teaches that trichlorosilane may be produced using a copper suicide catalyst. Margaria, et al. (US 6057469) describe copper deposited on the surface of silicon grains. Bulan, et al. (US Pat. Application 2004/0022713Al) indicate that to be effective copper must be in a granular form 30 to 100 times finer than the silicon particle. Alternatively, copper can be incorporated into the bulk of the silicon by adding copper in the form of elemental copper metal or as a copper compound to the silicon during metallurgical processing. However, such bulk incorporation must be at a much higher copper concentration in order to achieve the same catalytic effect than if the copper were applied only to the surface of the silicon. The higher concentrations of copper required by bulk addition poses challenges for effective disposal of the spent silicon containing the additional copper.

In all .such prior methods, considerable effort is put toward preparing a very finely divided form of copper and then having a carefully controlled method of bringing that fine form of copper together intimately and effectively with silicon material. Conducting the copper coating in a zone exterior to the hydrogenation reaction zone, e.g. Downing (US 4314908), also presents additional handling issues so as to prevent the treated material from reforming an oxide coating that will subsequently inhibit the hydrogenation reaction. These special methods invariably add cost and complexity to the overall production.

All of the prior methods fail to appreciate the effect of native surface oxide on silicon when considering the role of the promoter or catalyst. A native oxide on the silicon metal retards the effective bonding of copper to the silicon surface, which in turn, reduces the effective incorporation of the catalyst or delays the benefit of the catalyst until the native oxide can be removed by other chemical action within the process. The native oxide may be somewhat removed by extreme milling. But once the oxide is removed, the silicon must be maintained in an oxygen-free condition, a difficult and expensive process in practical commercial endeavors.

It thus would be useful to have a simplified method for forming an active catalyst specie so as to enhance the production of hydrochlorosilanes. With an effective and active catalyst, hydrochlorosilanes can be produced from the reaction of silicon and hydrogen along with a chlorine source. The chlorine source may be hydrogen chloride, silicon tetrachloride or a combination of the two. And, depending upon the objective, the ratio of dichlorosilane and trichlorosilane may be altered by adjusting the hydrogenxhloride ratio, gas residence time, and the reaction temperature and pressure when using the effective catalyst.

Detailed Description

To form an effective catalyst using silicon, the difficulties presented by a native oxide on the surface of silicon can be overcome by employing a reaction of the type where the silicon is first exposed to a reducing atmosphere to remove the surface oxide. Hydrogen gas at an elevated temperature can achieve this by the reaction:

H₂ + SiO₂ (solid) -> Si (metal) + H₂O (vapor) (4)

The resulting silicon surface is then substantially free of oxide if maintained in an oxygen- free environment.

Cuprous chloride is a reducible substance that rapidly reduces with hydrogen at elevated temperatures:

CuCl + H₂ -> 2 HCl + Cu (metal) (5)

The reduction of reaction (5) occurs autogenously at temperatures above about 275°C in a hydrogen atmosphere.

Commercially available metallurgical grade or refined grade silicon is used as a starting material in the production of trichlorosilane by reaction (1) or (2). Such silicon inherently has a native oxide present on the silicon surface. In the normal commercial practice, the silicon is milled and screened to provide a particle size suited to the particular requirements of the chosen process design. A particle size of about 200 microns is suitable in many processes, but size is of no issue so long as the particles are small enough to operate in a mixing environment, such as in a fluidized bed or stirred bed reactor, wherein gases readily can be brought into contact with the silicon particles.

By alloying the effective amount of copper onto the oxide-free silicon surface, the utilization of the copper is quite good and the amount of copper required to achieve the benefit is very low. This benefit is achieved by supplying additional amounts of copper and silicon, as needed, while the production of hydrochlorosilanes is proceeding at its normal temperature and pressure.

To produce hydrochlorosilanes generally according the reactions (1, 2, or 3), silicon is added into a vessel, such as a fluidized or mechanically stirred bed reactor, and the reactor is brought to normal operating conditions of 275⁰C - 550⁰C with a feed of gaseous hydrogen and a chlorine source. The chlorine source can be hydrogen chloride, silicon tetrachloride, or a combination thereof. In the absence of hydrogen chloride, the un-catalyzed, reaction:

SiCl₄ + H₂ -* HCl + HSiCl₃ (6)

not involving silicon, occurs and a small amount of HCl (< 1%) is formed. Temperature, reactor residence time, and hydrogen and chloride concentrations may be adjusted to produce the product mix required. HCl aggressively attacks the silicon at any temperature above 275⁰C by reaction (2). The combination of reactions (2) and (6) results in reaction (1). The effect of the silicon is to remove HCl from the reaction environment and shift the equilibrium concentration of reaction (1) to the right, increasing the overall yield of hydrochlorosilanes.

Concurrently, the surface of the silicon is attacked by the hydrogen to remove surface oxides and adsorbed moisture:

H₂ + SiO(H) -> Si + H₂O (7)

Reactions (6) and (7) are operated with an excess amount OfH₂. Together, reactions (6) and (7) combine to remove any oxides or moisture from at least a portion of the surface of the silicon. The resulting substantially oxide-free silicon surface is then able to effectively accept and bond with an active copper metal.

Copper, most effectively in form of cuprous chloride (CuCl), is then added to the reactor and the reduction with excess hydrogen at 275°C to 550⁰C occurs to form copper metal and additional HCl, by reaction (5). The copper, produced on an atomic basis, is deposited upon at least a portion of the substantially oxide-free surface of the silicon by chemical vapor deposition to form a copper-silicon alloy. In particular, particles of CuCl are reduced in situ in close proximity with the oxide-free silicon to form the effective alloy catalyst. The copper deposit may consist of randomly arranged "islands" of copper on the surface of the silicon. The copper-silicon surface alloy is a very effective catalyst for reactions (1), (2) and (3). Very effective results are obtained at copper levels of less than 1.0%. Particularly efficient operation is achieved when copper is from 0.01% to 0.5% of the mass of the copper-alloyed silicon. As an environmental impact consideration, the lower the copper use to achieve the required yield of hydrochlorosilanes the better, and the low levels identified herein are an order of magnitude lower than previously required.

Other reducible copper compounds may be employed in addition to or as a substitute for copper chloride. Copper oxide or mixtures of copper oxide and copper metal may be used. But when these are used, the extra moisture that is formed by the hydrogen reduction of the copper oxide results in a loss of chlorosilane by hydrolysis of the chlorosilanes to siloxanes, high boiling impurities that pose a difficult problem in disposal. Another suitable reducible material is chloroplatinic acid. When silicon tetrachloride is the chlorine source, the promoter metal should be chosen to be capable of promoting the hydrochlorination reaction in the presence of silicon tetrachloride and hydrogen. When the chlorine source is hydrogen chloride, the promoter metal should be a metal capable of promoting hydrochlorination of silicon in the presence of hydrogen chloride and hydrogen.

If a material, such as a promoter metal, is not associated with the silicon surface, it is ineffective in catalyzing reaction (1). For example, if a promoter metal is present on an otherwise non-reactive surface, such as silica or carbon, no promotional effect is noted. The promoter metal must be present at the surface of the silicon. The rapid consumption of silicon occurs only in the region immediately adjacent to the location of the promoter metal on the oxide-free silicon surface.

The promoter metal-silicon alloy need not be uniformly distributed on the surface of the silicon. It merely needs be present in an adequate amount. And the removal of the native oxide on silicon need not be complete or uniform, just sufficient to accommodate the amount of promoter metal to be deposited.

An elevated temperature is maintained to achieve the production of the one or more desired hydrochlorosilanes. To favor the production of trichlorosilane from silicon tetrachloride according to reaction (1), the temperature inside the reactor is best maintained at 400⁰C to 500⁰C. To favor the production of trichlorosilane and dichlorosilane from HCl according to reactions (2) and (3), the temperature inside the reactor is best maintained at 275°C to 350⁰C.

The reactor should be of a type that facilitates mixing of the de-oxidized silicon with the reducible substance that includes the promoter metal so that the decomposing reducible substance is transported to the surface of the silicon onto which the promoter metal is to be deposited. Particularly suitable reactors include fluidized bed reactors wherein moving gas provides the mixing force, mechanically agitated bed reactors such as rotary kiln and stirred bed reactors, and tower reactors wherein the silicon and copper chloride particles can fall by gravity against an upwardly rising stream of hydrogen rich gas. The hydrogenation reaction can also be carried out in a dilute phase (few solid particles relative to the reactor volume).

In a practical implementation of this process, fresh silicon is required to be added to the hydrochlorination reactor to maintain a substantially constant inventory as the silicon is consumed by reaction (1), (2) or (3) and hydrochlorosilanes are removed from the reactor. The granulated silicon can be fed either continuously or intermittently in small increments. By co-feeding cuprous chloride powder with the granulated silicon, a single, simplified system can be used. The cuprous chloride is thus preferably added directly to the reaction zone where it decomposes to copper and deposits onto the substantially oxide-free surface of the silicon already present in the reaction zone. The fresh silicon co-fed with the cuprous chloride enjoys a brief period of conditioning in the reaction zone to lose its native oxide and is thus prepared for reaction with the cuprous chloride being added at the next opportunity. By this procedure, one need not make any special arrangements to precondition either the silicon or the copper-containing substance and the overall effect is for a beneficially high rate of production of hydrochlorosilanes at normal temperature and pressure.

Other materials which can act to promote the hydrochlorination or to form proportionately higher yields of the more hydrogenated chlorosilanes can be added in a similar manner. In choosing the form of the promoter materials, best results are achieved with those forms that can be either vaporized at the reaction conditions or reduced by hydrogen at the elevated temperature present in the reaction zone to deposit a promoter metal. Such materials include the oxides, carbonates, and chlorides of zinc and tin and the chlorides and carbonates of ruthenium, rhenium, platinum, silver, osmium, and nickel. The following non-limiting examples demonstrate the implementation of this process:

EXAMPLE 1

A fluidized bed reactor 122 cm diameter was charged with 13,000 kg of metallurgical grade silicon ground to an average particle size of 200 micron. The reactor was started up by flowing 3350 m³/hr of hydrogen at a temperature of 500⁰C and a pressure of 3 Mpa. After the reactor reached operating temperature, silicon tetrachloride vapor at a flow of 3350 m³/hr was started at a temperature of 500⁰C and a pressure of 3 Mpa. A reactor product containing 20 mole % trichlorosilane on a hydrogen-free basis was obtained. When the reactor level decreased by 150 kg, by consumption of silicon via reaction (1), periodic addition of metallurgical grade silicon was commenced and the process continued in that manner for several days. After three days of operation, the equivalent of 72% of the original mass charge of silicon had been consumed and had been replaced with an equal amount of fresh metallurgical grade silicon. At that point, a blend of metallurgical grade silicon and cuprous chloride was prepared by adding 4.5 kg of cuprous chloride to a bulk bag containing 1363 kg of silicon. Using a pneumatic conveyor to transport the copper/silicon blend to a lock hopper atop the fluidized bed reactor, the copper/silicon blend was substituted for the normal metallurgical grade silicon feed to the reactor. Shortly after the addition of the cuprous chloride/silicon mix, the hydrogen consumption was noted to have significantly increased. The reactor product, on a hydrogen-free basis, increased to 25 mole % trichlorosilane. So long as the cuprous chloride/silicon was continued to be added to replenish the silicon consumed, the yield of trichlorosilane remained at the higher level. When the addition of copper chloride was terminated, the yield of trichlorosilane began to recede, eventually returning to its original level before the cuprous chloride feed had begun. The rate of decline indicated that copper had become associated with the silicon such that it was elutriated from the reactor only when the associated silicon particle was chemically etched to a size smaller than the entrainment size (~ 15 micron). Analysis of the reaction mass after the trichlorosilane conversion had returned to its pre-catalyst level indicated no copper had accumulated, while the copper level in the fine silicon elutriated from the reactor declined in direct proportion to the reduced yield of trichlorosilane.

This example shows that adding a reducible substance that contains a promoter metal directly to the reaction zone where oxide-free silicon is already present results in higher conversion to trichlorosilane. It also shows that the copper chloride had become intimately associated with the silicon and that the yield of trichlorosilane was directly related to the concentration of copper in the reaction mass.

EXAMPLE 2

5O g of ground metallurgical grade silicon (average particle size = 200 micron) was placed in a test tube of 25 mm diam. held in a small oven and heated with a flow of hydrogen to a temperature of 525°C. Silicon tetrachloride was placed in a thermostated reservoir held at 25⁰C. Provision was made to bubble hydrogen through the reservoir to saturate it with silicon tetrachloride and to then flow the saturated hydrogen, along with additional hydrogen to give a molar ratio of H₂:SiCl₄ of 2.0 into the bottom of the test tube containing the silicon. The total hydrogen flow was 12 cc/min. At the outlet of the reactor tube, a septum was installed to allow a small gas sample to be collected for gas chromatographic analysis. At a reactor temperature of 525°C, the yield of trichlorosilane was 4.6%.

EXAMPLE 3

Using the same apparatus as in Example 2, 49 g metallurgical grade silicon was placed into the reactor tube and heated to 525°C in a hydrogen atmosphere. After the silicon had been exposed to the hot hydrogen, 0.39 g of cuprous chloride were added to the reactor, while the hydrogen continued to flow. Then the hydrogen flow was routed through the thermostated reservoir of silicon tetrachloride and the effluent sampled. The concentration of trichlorosilane on a hydrogen free basis was 6.14%.

EXAMPLE 4

Using the same apparatus as in Example 2, the reactor was charged with 50 grams of silicon onto which previously had been deposited 1% platinum. When reacted at 525°C with the standard flow of hydrogen and silicon tetrachloride, the trichlorosilane concentration on a hydrogen-free basis was 6.05%. EXAMPLE 5

Using the same apparatus as in Example 2, the reactor was charged with a mixture of 49.9 g of metallurgical grade silicon and 0.1 gram of 5% Platinum on silica gel. The result was a trichlorosilane concentration, on a hydrogen-free basis of 4.28%.

EXAMPLE 6

Using the same apparatus as in Example 2, the reactor tube was filled with 49 g of white quartz and 0.1 gram of 5% platinum on activated carbon. Under the same standard conditions as used in Example 2, the trichlorosilane concentration in the effluent was < 0.1%.

In these illustrative examples, it is demonstrated that in order to promote the hydrogenation reaction, one must have both an active promoter metal and a source of metallic silicon. The absence of the promoter metal results in reduced yields (Example 2) and while in the absence of silicon, even with an active hydrogenation catalyst, no conversion takes place (Example 6). In order to provide the better conversion, the active promoter metal must be closely associated with the silicon (Examples 2 and 4 as compared with example 5).

EXAMPLE 7

Using the same apparatus as described in Example 2, the reactor can be charged with 50 grams of metallurgical grade silicon and heated to 300⁰C under a stream of 12 cc/min hydrogen and 6 cc/min hydrogen chloride. After the silicon is exposed to the hot hydrogen and hydrogen chloride mixture for several hours, 0.4 gram of cuprous chloride is added to the reactor, while the hydrogen/hydrogen chloride flow continues. When sampled as described in Example 2, the effluent contains trichlorosilane and several percent dichlorosilane. Without the copper-silicon alloy catalyst, the level of dichlorosilane would be only a trace.

In the present specification, methods for producing hydrogen-containing chlorosilanes have been described with reference to preferred embodiments. Other embodiments will be apparent to those skilled in the art from a consideration of this specification or practice of the methods disclosed herein. It is intended that the specification and examples be considered as exemplary only, with the true scope and spirit of the invention being indicated by the following claims.

Claims

1. A process for the production of one or more hydrochlorosilanes comprising reacting hydrogen, a chlorine source, and silicon particles onto which a hydrochlorination promoter metal has been deposited by a chemical vapor deposition comprising removing oxygen from the surface of the silicon particles, reducing a reducible substance comprising the hydrochlorination promoter metal, and depositing the hydrochlorination promoter material onto the silicon particles where the oxygen had been removed.

2. The process of claim 1 wherein the reacting is conducted at 275°C to 55O⁰C.

3. The process of claim 1 for the production of hydrochlorosilanes, including trichlorosilane and dichlorosilane, wherein: the chlorine source is silicon tetrachloride; and the promoter metal is a metal capable of promoting the hydrochlorination reaction in the presence of silicon tetrachloride and hydrogen.

4. The process of claim 3 wherein the reacting is conducted at 400⁰C to 500⁰C.

5. The process of claim 1 for the production of hydrochlorosilanes, including trichlorosilane and dichlorosilane, wherein: the chlorine source is hydrogen chloride; and the promoter metal is a metal capable of promoting hydrochlorination of silicon in the presence of hydrogen.

6. The process of claim 5 wherein the reacting is conducted at 275°C to 35O⁰C.

7. A process for the production of one or more hydrochlorosilanes comprising: removing oxygen from at least a portion of the surface of a silicon particle that has a surface oxide by heating the particle in a reducing atmosphere to produce a silicon particle having at least one oxide-free area; depositing a metal capable of promoting the hydrochlorination of silicon onto the oxide-free area to produce a promoter metal-silicon surface alloy by a chemical vapor deposition comprising the reduction of a reducible substance comprising the metal; and reacting hydrogen, a chlorine source, and the promoter metal-alloyed silicon to produce one or more hydrochlorosilanes.

8. The process of claim 7 wherein the removing, depositing, and reacting is conducted at 275°C to 55O⁰C.

9. The process of claim 7 for the production of hydrochlorosilanes, including trichlorosilane and dichlorosilane, wherein: the chlorine source is silicon tetrachloride; and the promoter metal is a metal capable of promoting the hydrochlorination of silicon in the presence of silicon tetrachloride and hydrogen.

10. The process of claim 9 wherein the removing, depositing, and reacting is conducted at 400⁰C to 500⁰C.

11. The process of claim 7 for the production of hydrochlorosilanes, including trichlorosilane and dichlorosilane, wherein: the chlorine source is hydrogen chloride; and the promoter metal is a metal capable of promoting hydrochlorination of silicon in the presence of hydrogen.

12. The process of claim 11 wherein the removing, depositing, and reacting is conducted at 275⁰C to 350⁰C.

13. A process for the production of one or more hydrochlorosilanes comprising: combining hydrogen, a chlorine source, and silicon that has a surface oxide; heating the hydrogen, chlorine source, and silicon to a sufficient temperature that oxygen is removed from at least one area of the surface of the silicon; contacting the silicon having an oxide-free area with a reducible substance that includes a metal capable of promoting hydrochlorination of the silicon; heating the reducible substance to a sufficient temperature that the substance is reduced and the metal is deposited onto the oxide-free area to produce a promoter metal- silicon surface alloy; and reacting the hydrogen, chlorine source, and promoter metal-alloyed silicon to produce one or more hydrochlorosilanes.

14. The process of claim 13 wherein the heatings are to 275⁰C to 55O⁰C and the reacting is conducted at 275⁰C to 55O⁰C.

15. The process of claim 13 for the production of hydrochlorosilanes, including trichlorosilane and dichlorosilane, wherein: the chlorine source is silicon tetrachloride; and the promoter metal is a metal capable of promoting the hydrochlorination of silicon in the presence of silicon tetrachloride and hydrogen.

16. The process of claim 15 wherein the heatings are to 400⁰C to 500⁰C and the reacting is conducted at 400⁰C to 500⁰C.

17. The process of claim 13 for the production of hydrochlorosilanes, including trichlorosilane and dichlorosilane, wherein: the chlorine source is hydrogen chloride; and the promoter metal is a metal capable of promoting hydrochlorination of silicon in the presence of hydrogen.

18. The process of claim 17 wherein the heatings are to 275⁰C to 35O⁰C and the reacting is conducted at 275°C to 35O⁰C.

19. The process of claim 1, 7, or 13 wherein the promoter metal is less than 0.1% of the mass of the promoter metal-alloyed silicon.

20. The process of claim 1, 7, or 13 wherein the promoter metal is 0.01% to 0.5% of the mass of the promoter metal-alloyed silicon.

21. A process as in claim 1, 7, or 13 wherein the reducible substance is cuprous chloride.

22. The process of claim 1, 7, or 13 wherein the reducible substance is copper oxide.

23. The process of claim 1, 7, or 13 wherein the reducible substance is chloroplatinic acid.

24. A process for the production of one or more hydrochlorosilanes comprising: in a vessel, heating a mixture comprising hydrogen, a chlorine source, and silicon that has a surface oxide at a temperature and for a time sufficient that oxygen is removed from at least a portion of the surface of the silicon; contacting a reducible substance that includes a metal capable of promoting hydrochlorination of silicon with the silicon having an at least partially oxide-free surface inside the vessel in a reducing atmosphere at a temperature sufficiently high that the substance is reduced and the metal is deposited onto the oxide-free surface of the silicon to produce a promoter metal-silicon surface alloy; and reacting the hydrogen, chlorine source, and promoter metal-alloyed silicon inside the vessel to produce one or more hydrochlorosilanes.

25. A process for forming a promoter metal-bearing reaction mass, the process comprising maintaining silicon particles, hydrogen, a chlorine source, and a reducible substance that includes a metal capable of promoting hydrochlorination in the vessel at 275°C to 550⁰C and for a time sufficient that oxygen is removed from the surfaces of the silicon particles, the reducible substance is reduced, and the metal deposits on the surfaces of the silicon particles by chemical vapor deposition to form a promoter metal-silicon surface alloy.

26. The process of claim 25 wherein: the reducible substance is cuprous chloride; and the metal is copper, which is deposited on at least a portion of the surface of the silicon by chemical vapor deposition to form a copper-silicon surface alloy.