JPH0448725B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention relates to a method for treating residual silicon powder, and more particularly to a method for producing chlorosilane from residual silicon powder.

Commercial methods of making organohalosilanes are well known and are described in Rochow, US Pat. No. 2,380,995. Rochow describes the direct reaction of organic halides, such as methyl chloride, with silicon particles to produce organochlorosilanes. Such silicon particles are mixed with copper particles, thereby forming a reactive material or reactive contact material. Commercially, this reaction is generally carried out in one of three types of equipment: a stirred bed reactor, such as that described in Sellers, U.S. Pat. No. 2,449,821; Reed et al., U.S. Pat.
2389931; or a rotary kiln.

Organotrichlorosilane and diorganodichlorosilane are the two basic products of the above direct reaction. Such compounds are covered by U.S. Pat.
It is used in the production of organopolysiloxane resins as described in Nos. 2258218 to 2258222. Other products include organopolysiloxane fluids such as those described in U.S. Pat. No. 2,469,888 and U.S. Pat. No. 2,469,890;
There are organopolysiloxane elastomers such as those described in No. 2448756. Generally, it is preferred to produce the diorganodichlorosilane commercially. This is because they are commonly utilized in the production of linear polysiloxane fluids and polymers used in the production of thermoset rubber elastomers and various types of room temperature vulcanizable silicone rubber compositions.

At a certain stage in the direct method of producing organochlorosilane, the reactivity of the reactive substance containing silicon particles or the reactive contact substance decreases, and it is therefore preferable to replace the reactive substance. Therefore, the old or less reactive silicon particles are removed from the reactor, new silicon particles are introduced, and the reaction is then restarted. When a reactive contact material becomes less reactive and is replaced by fresh silicon content, this less reactive contact material is generally combined with residual silicon, residual silicon powder, residual silicon-containing welding material, or residual contact material. Called. These terms can be used interchangeably here. An early solution to this problem was to discard the residual contact material, but significant reactive silicon remains in the residual contact material, and for economic reasons and to avoid waste disposal problems, it was necessary to discard the residual contact material. Preferably, at least some of the remaining silicon value in the contact material is utilized.

Much work has been done to find ways to more fully utilize the residual silicon particles in the reactors used to carry out the direct synthesis of organochlorosilanes. As a result, if the weight ratio of organotrichlorosilane (denoted as T) to diorganodichlorosilane (denoted as D) can be maintained at a desired level for an extended period of time, silicon particles are maximally utilized in the production of diorganodichlorosilane. I found out that it became possible to In the production of organochlorosilane by Rochow's direct method, during the production of chlorosilane,
The weight ratio of triorganochlorosilane to diorganodichlorosilane (T/D) should not exceed about 0.1, preferably about 0.35. However, in many commercial manufacturing operations, it has been found that while this ratio is at a level of about 0.15 when starting the reactor with fresh feedstock, after the reaction period this increases to levels above 0.2. One improvement in this range is the method of Dotson, US Pat. No. 3,133,109. Dotson revealed that silicon particles can be more fully utilized and that the amount of diorganodichlorosilane can be maximized by passing the particles from a fluidized bed reactor to an external fluid energy mill. ing. Separate from the external fluid energy mill, Dotson also passes the used silicon particles recycled from the reactor through a number of sonic jet nozzles located at the bottom of the reactor to prevent particles from colliding with each other or with the reactor walls. It is also mentioned that the particles are crushed by pulverization.

By utilizing the Dotson method, a larger amount of diorganodichlorosilane is obtained from the same amount of silicon particles, so that the above ratio can be kept near the desired level of 0.15 and kept below 0.35 for an extended period of time. I found out that it was dripping. However, in the Dotson method, approximately 12
It was found that ~15% was underutilized and had to be removed from the process as waste silicon. Generally, such silicon is exhausted;
It was therefore considered no longer available. It is desirable to utilize this waste silicon to avoid the problems normally encountered in waste disposal and for economic reasons. Furthermore, it would be further desirable to find a new method that can utilize substantially all of the silicon number in the residual silicon-containing contact material after the T/D ratio rises to an undesirable level.

U.S. Pat. No. 4,281,149 to Shade shows a method for processing silicon particles in such a silicon reactor system, thereby improving the usefulness of silicon metal particles. The Shade process generally processes silicon particles with an average diameter of less than 40 microns, then polishes such particles to remove the surface coating on the particles, and then returns the polished particles to the reactor for further utilization. There are many ways in which it can be done.

U.S. Patent Nos. cited herein as references
No. 4,307,242, Shah and Ritzer show another method for recovering and recycling silicon particulates in organochlorosilane reaction systems. The method described therein classifies the direct contact material by particle size, thereby separating the most severely damaged or contaminated (spent) silicon particles from the relatively intact silicon particles. , and a method of recycling only such intact particles to improve the availability of silicon. Therefore, instead of discarding all of the used silicon particles from the direct process, only a small amount of the used silicon particles need to be discarded at any given time. No. 4,307,242, effluent fines (residual contact material or residual silicon)
is collected by one or more mechanical cyclones. This effluent fines is generally spent reactant from reactors that produce organotrichlorosilane and diorganodichlorosilane products. The T and D crude products are collected from the top of the cyclone. These products may contain "microfine" particles entrapped therein. The remaining reactants are treated with air in a mechanical cyclone and placed in a receiving hopper for further disposal. At any stage described by Shah and Ritzer, especially
Preferably, useful products are obtained from the second cyclone particulates obtained from the Shah and Ritzer classification method. It would still be desirable to obtain useful products from silicon and residual silicon-containing contact materials obtained from any other source.

One such useful product obtained from various reactions with silicon is trichlorosilane (HSiCl ₃ ). A well-known use of trichlorosilane is the hydrosillation reaction of trichlorosilane to create organofunctional silanes, as discussed in British Patent Application GB 2028289 published March 5, 1980 by Woerner et al. This is the use of trichlorosilane as a raw material for the production of ultra-pure silicon. Woerner et al. show that trichlorosilane and silicon tetrachloride are made by the reaction of silicon and hydrogen chloride. Additionally, Rochow in U.S. Patent No. 2,380,995 claims that approximately 80%
Compt.rend.Combes reports that a mixture of about 20% trichlorosilane and about 20% silicon tetrachloride can be obtained by passing hydrogen chloride through a silicon-filled iron tube heated to 300°C to 440°C. 122 , 531 (1896), reported the reaction between hydrogen chloride and silicon. It would thus be desirable to provide additional sources of trichlorosilane, to provide an economical process for making trichlorosilane, and to provide a process for the synthesis of trichlorosilane in which the yield of trichlorosilane is improved. ing.

SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide a method for utilizing residual silicon obtained in the production of organochlorosilanes.

Another object of the invention is to provide an improved process for obtaining trichlorosilane from silicon.

Another object of the present invention is to provide a method for producing trichlorosilane from residual silicon powder.

Other objects and advantages of the invention will become apparent from the detailed description below.

According to the purpose of the present invention, trichlorosilane is
It is produced by contacting residual silicon powder with an anhydrous chlorine source selected from the group consisting of hydrogen chloride, chlorine, and mixtures thereof in the presence of silicon tetrachloride vapor at elevated temperatures.

In accordance with the purposes of the present invention, the residual silicon or residual silicon-containing contact material is an anhydrous chlorine source selected from the group consisting of hydrogen chloride, chlorine and mixtures thereof;
A method is described for producing trichlorosilane from residual silicon obtained from the direct production of organochlorosilanes or from residual silicon-containing contact materials, which comprises contacting in the presence of silicon tetrachloride vapor at elevated temperatures.

Generally, silicon tetrachloride vapor is utilized as a carrier gas and is also a fluidizing medium for granular or powdered silicon or silicon-containing sources or contact materials. To make trichlorosilane, hydrogen chloride gas and/or chlorine gas may be mixed with a silicon tetrachloride carrier gas. In the process of the invention it is important that an external source of silicon tetrachloride is fed into the reactor together with hydrogen chloride or chlorine gas. By external source is meant a source other than the products obtained during the reaction.

In the process of the present invention, the residual silicon-containing contact material obtained as second particulates from the cyclone separator is treated with an anhydrous chlorine source in the presence of added silicon tetrachloride vapor to form organohalosilanes. Residual silicon-containing contact material resulting from direct process production was converted to trichlorosilane. As explained above, the silicon tetrachloride vapor stream may contain hydrogen chloride gas and/or chlorine gas, or separate streams of silicon tetrachloride and hydrogen chloride gas and/or chlorine gas may be added to the reactor or reaction chamber. It may be introduced into Additionally, silicon tetrachloride is an inherent by-product in the direct synthesis of trichlorosilane and is therefore an ideal carrier gas for the process of the present invention and subsequent recycling. External silicon tetrachloride used in the process of the invention can also be collected and recycled. When the trichlorosilane product, which generally has a boiling point of about 31.5°C, is recovered, silicon tetrachloride, which generally has a boiling point of about 57.6°C, is also recovered.
For example, when they are collected by condensation methods, they generally condense at the same time and form a mixture. This mixture can be distilled or subjected to another separation process to separate the trichlorosilane from the silicon tetrachloride, which is then stored and recycled or converted into silicon tetrachloride for the process of the invention. can be immediately recycled as an external source of The silicon tetrachloride by-product mentioned above, dichlorosilane (H ₂ SiCl ₂ ),
By-products of the reaction are also formed during the reaction, including monochlorosilane (H ₃ SiCl), high boilers such as hexachlorodisilane (Cl ₃ Si-SiCl3), etc., and these by-products can also be removed by conventional separation if desired. and can be separated and recovered by a recovery method.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a process for the preparation of trichlorosilane comprising contacting silicon with hydrogen chloride and/or chlorine in the presence of an external source of silicon tetrachloride at elevated temperatures. As used herein, silicon is residual silicon obtained from direct synthesis or production of organochlorosilanes.

The silicon may be in any finely divided form, and for optimum results the silicon in the reactor should generally have an average particle size in the range of about 20 to about 200 microns. Preferably, the actual diameter of at least 25% by weight of the silicon particles ranges from about 20 to about 200 microns.

The residual silicon powder may also contain other auxiliaries and additives previously added to the elemental silicon for the production of the organochlorosilane. Direct synthesis or production of organosilanes is described in Rochow, US Pat. No. 2,380,995. The present invention
For example, after Rochow's direct synthesis, it may be carried out without further processing of the residual contact material remaining, but in a preferred embodiment, the contact material is further processed to remove some of the auxiliaries and additives. They do not contaminate trichlorosilane (HSiCl ₃ ) products. To this end, in preferred embodiments, various conventional methods are applied to the residual silicon-containing material before carrying out the method of the invention. For example, residual contact substances are listed as a reference here.
It may be processed as described in US Pat. No. 4,307,242 to Shah and Ritzer, in which the silicon-containing contact material, referred to as "effluent contact material powder" or alternatively referred to as "silicon particulates", is subjected to an aerodynamic or centrifugal classifier. There is. Such a classifier is a device that can classify and separate cyclone fine particles according to particle size. The most common method involves recycling the relatively coarse particulates into the organochlorosilane reactor and discarding the finest portion. However, according to Shah and Ritzer, the so-called finest fraction contains by far the highest percentage of non-silicon impurities, and decisions must be made about which grain sizes to discard and which grain sizes to recycle. . Thus, the Shah and Ritzer direct method for purifying silicon metal contact material from an organohalosilane reactor system analyzes a portion of the reactor contact material for particle size distribution; sorting into a first part and a relatively impure second part; and separating the first and second parts. The silicon particles are collected by a second cyclone and sent to a receiving hopper and then to a transfer hopper.
From there it is sent to a mechanical classifier, preferably an aerodynamic or centrifugal classifier. In a preferred embodiment of the invention,
The second cyclone particulate is contacted with a suitable source of anhydrous chlorine, such as hydrogen chloride, chlorine, and mixtures thereof, at elevated temperature in the presence of an external source of silicon tetrachloride.

Another preferred source of residual silicon is finely divided particles of silicon obtained from the method and apparatus described in Dotson, US Pat. No. 3,133,109, incorporated herein by reference. Dotson passes the silicon-containing use particles from the fluidized bed reactor through an external fluid energy mill or passes them through a number of sonic jets at the bottom of the reactor to pulverize the particles or or crushing the particles by impacting the silicon particles against the reactor wall. Thus, any residual silicon-reactive material that has been crushed, crushed or disintegrated by breaking up individual particles of the silicon-containing mixture by compression, impact, attrition, etc. may be used in the process of the present invention.

As mentioned above, the silicon source may be a new silicon powder that has not yet been used in the manner described above. Thus, any finely divided silicon, preferably finely divided silicon that is free of any contaminants that could cause contamination of the final product, such as trichlorosilane, may be used in the process of the present invention.

Although there are no limitations regarding the equipment for carrying out the method of the present invention, the equipment may include silicon as an anhydrous chlorine source;
It must be possible to make sufficient contact in the presence of silicon tetrachloride at high temperature. The reactor or reaction chamber may be of any suitable size or shape and is preferably made of a material that will not be corroded by or react with the reactants and products and/or by-products. The apparatus is capable of heating the residual silicon powder at a suitable elevated temperature sufficient to effect a reaction between the residual silicon powder and the chlorine source in the presence of an external source of silicon tetrachloride to produce trichlorosilane. Must be able to do it. In one preferred embodiment, the method is carried out by forming a fluidized bed, and while the silicon remains in the fluidized bed, the silicon is contacted with the anhydrous chlorine source and silicon tetrachloride. There are various examples for maintaining a fluidized bed of silicon, including ensuring that the gas or vapor velocity is sufficient to maintain the silicon in a fluidized state within the reactor.
This is preferably carried out by injecting silicon tetrachloride as a carrier, ie as a fluidizing medium, into the granular silicon. Of course, other conventional fluidization means may also be used to maintain the silicon bed in a fluidized state while simultaneously contacting it with a source of anhydrous chlorine in the presence of silicon tetrachloride, and to maintain the silicon bed in a fluidized state. It is also within the scope of the invention to utilize a combination of measures. Inert gases, such as nitrogen, can be used to fluidize the residual silicon powder or to assist other fluidizing means, although they are generally not preferred because of the need for powerful evacuation means. A conventional fluidized bed reactor is described in Reed et al. US Pat. No. 2,389,931. Another means of contacting silicon with an anhydrous chlorine source and silicon tetrachloride includes Sellers, U.S. Pat.
a stirred bed reactor as described in No. 2449821;
Alternatively, there is a method using a conventional rotary kiln. The means for heating the silicon bed within the reactor may be any conventional means, and internal and external heating sources, including gas and/or steam heating, may be used in the process of the present invention. Examples of conventional means of heating beds contained therein are presented in the above-mentioned documents.

The high temperature at which the reaction mixture of residual silicon powder, anhydrous chlorine source, and silicon tetrachloride is heated is not limited as long as the temperature is sufficient to produce trichlorosilane product from the reaction mixture. Generally, temperatures from about 230<0>C to about 350<0>C are suitable for the production of trichlorosilane from the reactants.

Any anhydrous chlorine source may be used in the process of the present invention, so long as it is possible to produce trichlorosilane from the reaction between silicon and chlorine in an anhydrous chlorine source used in conjunction with an external source of silicon tetrachloride. . Preferred sources of anhydrous chlorine are hydrogen chloride gas, chlorine gas, and mixtures thereof. The amount of chlorine source is
It only needs to be in an amount sufficient to form trichlorosilane from the silicon contact material. Of course, the reaction rate is proportional to the amount of chlorine sources present in the reaction mixture, and silicon tetrachloride acts as their dilution medium. The amount of chlorine source required by the desired reaction rate in the particular reaction system or reactor utilized in the production of trichlorosilane can be determined by one skilled in the art. In certain preferred embodiments, the chlorine source is about 10.0 mol% to
In other words, silicon tetrachloride is about 1.0 mole percent to about 90.0 mole percent of the silicon tetrachloride-chlorine source.
It is mole%. In the most preferred embodiment, the silicon tetrachloride to hydrogen chloride gas ratio, on a molar basis, is about
1.3:1 to about 2.6:1. Hydrogen chloride gas and/or chlorine gas may be any conventional gas source provided in commercial applications.

Silicon tetrachloride from an external source may also be from any suitable source. Silicon tetrachloride is an inherent byproduct of the direct synthesis of trichlorosilane, and any silicon tetrachloride formed as a byproduct of the reaction of the present invention is collected and recycled as an external source of silicon tetrachloride in the present invention. I can do it. It is therefore ideal for use as a carrier gas, which can then be recycled from the reactor for further use in the process of the invention. Silicon tetrachloride from external sources can also be collected and recycled for further use. Thus, when collecting the trichlorosilane product, silicon tetrachloride can be collected both from external sources and as a by-product. One way to collect
By condensing in a conventional condenser cooled to about -20°C with a methanol-based coolant. This condenses the product, silicon tetrachloride and most by-products. These may be suitably collected and then separated by any suitable separation method, including fractional distillation.

Anhydrous chlorine sources, such as hydrogen chloride gas and/or chlorine gas, and silicon tetrachloride can be brought into contact with the silicon in a suitable manner and the gas(es) or vapors are introduced into the reaction chamber in which the reaction is carried out. Any suitable gas velocity that supplies the gas may be used. In preferred embodiments where silicon tetrachloride vapor is the silicon fluidizing medium, the gas velocity is sufficient to maintain the silicon bed in a fluidized state. Generally, the silicon tetrachloride gas velocity is about 3 to about 15 times the flow velocity of the residual silicon powder. The optimum rate of gas and/or steam can be determined by one skilled in the art and is based on various operating conditions. When using a stirred bed reactor or when using a rotary kiln,
The gas velocity or flow rate can be lower than the minimum velocity required to fluidize the silicon in the reactor.

If silicon tetrachloride gas or steam is used with the anhydrous chlorine source, in preferred embodiments hydrogen chloride gas and/or chlorine gas is co-fed to the reaction chamber with the silicon tetrachloride stream. However, it is within the scope of the invention to supply separate streams of gas to the reactor as well as multiple streams of gas to the reactor and combinations thereof. Silicon tetrachloride is not only a byproduct of the direct production process for organochlorosilanes, but it is also collected, separated, and recycled to the reactor for contacting the silicon with an anhydrous chlorine source in the presence of silicon tetrachloride. The use of silicon tetrachloride is advantageous in the process of the present invention because of its ease of preparation. Thus, in accordance with at least some of the objects of the present invention, silicon tetrachloride is used as a diluent for the chlorine source and/or as a carrier gas and/or as a fluidizing medium, and when silicon tetrachloride is used in the present method. Significant improvements have been recognized. The trichlorosilane product is also collected by any suitable means, such as the use of a condenser and subsequent distillation.

Generally, it is preferred to carry out the process of the present invention under anhydrous conditions to prevent the formation of hydrolysis byproducts and other undesirable byproducts that reduce the yield of trichlorosilane. Accordingly, preferred embodiments may employ steps to remove moisture from the system and reactants.

The following examples illustrate the invention:
Without limiting the scope of the invention: a 2.54 cm diameter, 45.7 cm (18 inch) long, 2.54 cm (2.54 cm) diameter, 45.7 cm (18 in.) long plug with a special flanged end and an electric motor-driven discontinuous helical agitator for bed agitation. A 1 inch (2.54 cm) stirred bed reactor made of tubular stainless steel was used as the reactor.
The tube section was divided into upper and lower reaction zones and each reaction zone was fitted with an independent heater to maintain each zone at the desired temperature. The reactor barrel or tube was well insulated to prevent heat loss. Inlets were made at the bottom of the tube for supplying sources of gas and/or steam, ie silicon tetrachloride and chlorine sources. An outlet was made at the top of the tube and equipped with a suitable condenser for collecting the liquid trichlorosilane product and by-products and a suitable vent for degassing. Appropriate glass and plastic fittings and tubing were used to minimize the corrosive effects of reactive gases.

Second cyclone particles as described above obtained from the method described in Shah and Ritzer U.S. Pat. No. 4,307,242
50.0 g of residual silicon-containing contact material was placed into the stirred bed reactor system described above. The temperature of the reaction zone was maintained at approximately 250°C during the experiment. Anhydrous hydrogen chloride was passed through a linear flow meter at a rate of 2.45 g/hour (0.067 g/hour).
molar) was fed into the reaction zone at a constant rate. The feeding rate of silicon tetrachloride varied, but it was 14.7 to 29.4 g/hour.
(about 0.09 to about 0.17 mol per hour). Therefore, the silicon tetrachloride to hydrogen chloride ratio (moles) is approximately 1.3 to approximately 2.6.
was kept within the range. A slight purge of Grade 5 nitrogen gas was introduced at all times to ensure that the silicon tetrachloride passed through the preheater-evaporator two-part zone maintained at approximately 125°C to the contact material bed region. I let it be carried. Trichlorosilane (HSiCl ₃ ) was initially observed in the reaction effluent by gas chromatographic analysis.

Thus, in accordance with the objectives of the present invention, trichlorosilane was produced from residual silicon powder recovered from the production of organochlorosilane by the direct process.
Anhydrous hydrogen chloride is added to the silicon tetrachloride vapor; the hydrogen chloride in the resulting silicon tetrachloride vapor is passed through a bed of residual silicon powder to form a reaction mixture; and the reaction mixture is heated at an elevated temperature to form trichlorosilane. A method for processing residual silicon powder recovered from the production of organochlorosilane by a direct process has been described.

Although the present invention has been described in detail with reference to particularly preferred embodiments, it goes without saying that modifications can be made within the spirit and scope of the invention.

Claims (1)

[Claims] 1. Trichlorosilane is produced by contacting silicon with an anhydrous chlorine source selected from the group consisting of hydrogen chloride, chlorine, and mixtures thereof at a temperature of about 230 to 250°C in the presence of silicon tetrachloride. In the method for manufacturing, the silicon is derived from residual silicon obtained when producing organochlorosilanes, the silicon tetrachloride is supplied from an external source, and the silicon tetrachloride and the chlorine source are The molar ratio is approximately 1.3:
1 to about 2.6:1. 2. The method of claim 1, wherein the silicon is a powder and the chlorine source and silicon tetrachloride are contacted with a fluidized bed of silicon powder. 3. The method of claim 1, wherein the silicon is a powder and the chlorine source and silicon tetrachloride are contacted with a stirred bed of silicon powder. 4. The method according to claim 1, wherein silicon tetrachloride is a carrier for the chlorine source. 5. The method according to claim 1, wherein silicon tetrachloride is the silicon fluid medium. 6. The method of claim 1 further comprising collecting the trichlorosilane product and silicon tetrachloride and separating the trichlorosilane and silicon tetrachloride. 7. The method of claim 1 further comprising collecting the trichlorosilane product and silicon tetrachloride, separating the trichlorosilane and silicon tetrachloride, and recycling the silicon tetrachloride. 8. A method for treating residual silicon powder recovered during the production of organochlorosilane, comprising the following steps: (a) Anhydrous chlorine source selected from the group consisting of hydrogen chloride, chlorine and mixtures thereof is converted into silicon tetrachloride vapor. (provided that the silicon tetrachloride is supplied from an external source and the molar ratio of the silicon tetrachloride to the chlorine source is from about 1.3:1 to about
The ratio is 2.6:1. ), (b) passing the resulting chlorine source in silicon tetrachloride vapor through a bed of residual silicon powder to form a reaction mixture, and (c) heating the reaction mixture at a temperature of about 230-250°C to Forms chlorosilane. 9. The method according to claim 8, further comprising recovering trichlorosilane. 10. The method of claim 8, further comprising forming a fluidized bed of residual silicon powder. 11. The method of claim 10, wherein the bed is fluidized by the velocity of silicon tetrachloride vapor. 12. The method of claim 8, further comprising forming a stirred bed of residual silicon powder. 13. The method of claim 8 further comprising collecting the trichlorosilane product and silicon tetrachloride and separating the trichlorosilane and silicon tetrachloride. 14. The method of claim 8 further comprising collecting the trichlorosilane product and silicon tetrachloride, separating the trichlorosilane and silicon tetrachloride, and recycling the silicon tetrachloride.