JP7500378B2 - Method for producing trichlorosilane - Google Patents

Description

The present invention relates to a method for producing trichlorosilane, which is used as an intermediate raw material for high-purity silicon. More specifically, the present invention relates to a method for producing trichlorosilane by mixing heat transfer medium particles for conducting reaction heat in a fluidized bed reactor.

Trichlorosilane can be obtained by reacting a silicon raw material with a purity of about 98%, known as metallic silicon, with hydrogen chloride gas. Because the chlorination reaction in this process generates a large amount of heat, a fluidized bed reactor with high thermal uniformity is used to control the temperature inside the furnace.

Since silicon tetrachloride is inevitably produced in the chlorination reaction, methods have been disclosed for increasing the selectivity of trichlorosilane while suppressing the production of silicon tetrachloride (see, for example, Patent Document 1 (claims 1 to 6, paragraphs [0008], [0025], and [0026]) and Patent Document 2 (claims 1, 3, 4, and paragraph [0021])).

Patent document 1 discloses a method for producing trichlorosilane by reacting silicon with HCl gas in a fluidized bed reactor, a stirred bed reactor or a solid bed reactor at a temperature of 250°C to 1100°C and at an absolute pressure of 0.5 to 30 atm. In this method, the silicon fed to the reactor is characterized in that it contains 40 to 10,000 ppm by mass of barium and, optionally, 40 to 10,000 ppm by mass of copper.

Patent Document 1 describes that this production method can increase the selectivity of trichlorosilane, and describes that barium and, optionally, copper are alloyed with silicon, or that barium or a barium compound is mechanically mixed with silicon before the silicon is fed to the reactor, or that copper or a copper compound is mechanically mixed with silicon before the silicon is fed to the reactor, and further describes that barium or a barium compound is added to the reactor separately from silicon. On the other hand, it describes that when only copper is alloyed with silicon, it has no effect on the selectivity of trichlorosilane.

Patent Document 2 also discloses a method for producing trichlorosilane by reacting silicon with HCl gas in a fluidized bed reactor, stirred bed reactor, or fixed bed reactor at a temperature of 250°C to 1100°C and an absolute pressure of 0.5 to 30 atm, characterized in that the silicon supplied to the reactor contains chromium in the range of 30 to 10,000 ppm.

Patent Document 2 describes that the selectivity of TCS in the production of trichlorosilane can be improved by adding chromium to silicon, and describes that chromium is alloyed with silicon or that chromium is mechanically mixed with silicon before the silicon is fed to the reactor.

In addition, Non-Patent Document 1 reports that in a method of alloying metal silicon by adding an iron alloy, the alloy layer becomes a reactive active site, and the increased reactivity lowers the reaction initiation temperature, resulting in improved selectivity to trichlorosilane. On the other hand, Non-Patent Document 2 reports that the effect of phosphorus (P) added to metal silicon conversely reduces the selectivity to trichlorosilane.

JP 2013-535399 A JP 2007-527352 A

Reactor studies of the trichlorosilane process, G. Andersen, J. Hoel, H. A. Oye, Silicon for Chemical Industry V, (2000) 198-199 Study on selectivity in trichlorosilane producing reaction, S. Wakamatsu, K. Hirota, K. Sakata, Silicon for Chemical Industry IV, (1998) 129-131

When alloying barium or copper with silicon in the method of Patent Document 1, when alloying chromium with silicon in the method of Patent Document 2, or when alloying metal silicon by adding an iron alloy as shown in Non-Patent Document 1, it is necessary to dissolve barium or copper, dissolve chromium, or prepare the iron alloy in advance before putting it into the reactor, which creates a problem of complicating the manufacturing process.

In addition, consistent with the report in Non-Patent Document 2, as shown in Example 1 (prior art) of Patent Document 1, there was an issue that the selectivity to trichlorosilane could not be increased even if only copper was mixed with silicon.

The object of the present invention is to solve the above problems by taking an approach from a completely different perspective than the technical ideas of Patent Documents 1 and 2 and Non-Patent Document 1, and to provide a method for producing trichlorosilane that can improve the yield of trichlorosilane.

A first aspect of the present invention is a method for producing trichlorosilane by reacting metal silicon particles with hydrogen chloride gas in a fluidized bed reactor, characterized in that heat transfer medium particles having an average particle size smaller than that of the metal silicon particles, a density higher than that of the metal silicon particles, and being inactive and non-hygroscopic with respect to the hydrogen chloride gas are mixed with the metal silicon particles in the fluidized bed reactor , and the heat transfer medium particles are iron particles or iron compound particles mainly composed of iron containing one or more elements selected from the group consisting of oxygen, chromium, and nickel.

A second aspect of the present invention is a method for producing trichlorosilane based on the first aspect , wherein the average particle size of the metal silicon particles is 200 μm to 500 μm, and the average particle size of the heat transfer medium particles is smaller than the average particle size of the metal silicon particles and is 10 μm or more.

A third aspect of the present invention is a method for producing trichlorosilane based on the first or second aspect , wherein the heat transfer medium particles are mixed with the metal silicon particles in a ratio of 1 vol % to 3 vol %, where the total volume of all particles constituting the fluidized bed in the fluidized bed reactor is 100 vol %.

In the method of the first aspect of the present invention, when metal silicon particles are reacted with hydrogen chloride gas in a fluidized bed reactor, heat transfer medium particles that have a smaller average particle size than the metal silicon particles, a larger density than the metal silicon particles, are inactive to hydrogen chloride gas, and are non-hygroscopic are mixed with the metal silicon particles, so that the heat transfer medium particles do not participate in the chlorination reaction and only contribute to heat conduction in the fluidized bed reactor described below. This makes it possible to suppress local temperature increases in the fluidized bed reactor and improve the yield of trichlorosilane. Non-Patent Document 1 reports that if the temperature inside the furnace is high, the yield of trichlorosilane deteriorates.

In addition, since the heat transfer medium particles used are iron particles or iron compound particles mainly composed of iron containing one or more elements selected from the group consisting of oxygen, chromium, and nickel, the heat transfer is high and local temperature increases in the fluidized bed reactor can be suppressed, thereby improving the yield of trichlorosilane.

In the method of the second aspect of the present invention, the heat transfer medium particles have an average particle size smaller than that of the silicon metal particles and at least 10 μm. Therefore, the heat transfer medium particles flow smoothly together with the silicon metal particles in the fluidized bed reactor and are uniformly distributed throughout the fluidized bed reactor. This makes it possible to more efficiently suppress localized temperature increases in the reactor, thereby improving the yield of trichlorosilane.

In the method of the third aspect of the present invention, when the total volume of all particles constituting the fluidized bed in the fluidized bed reactor is taken as 100 volume %, the heat transfer medium particles are mixed with the metal silicon particles in a ratio of 1 volume % to 3 volume %, so that the heat transfer medium particles are mixed with the metal silicon particles in just the right amount, making it possible to more efficiently suppress localized temperature increases in the reactor and thereby improve the yield of trichlorosilane.

FIG. 1 is a schematic diagram of a fluidized bed reactor for producing trichlorosilane according to an embodiment of the present invention. FIG. 2 is a graph showing the change in yield of trichlorosilane in Example 1 of the present invention.

Next, the embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the fluidized bed reactor 10 for producing trichlorosilane in this embodiment includes an apparatus body 11 having a roughly cylindrical body 12, a bottom plate 13, and a top plate 14. A particle supply port 15 for supplying metal silicon particles into the apparatus body 11 is formed at the bottom of the body 12 of the apparatus body 11. A carrier gas inlet 30 is connected to this particle supply port 15, and metal silicon particles and heat transfer medium particles are supplied from a feed hopper 31 to this carrier gas inlet 30, and are supplied into the apparatus body 11 via this particle supply port 15. In addition, a gas outlet 17 for taking out trichlorosilane gas generated by the reaction to the outside is provided on the top plate 14 of the apparatus body 11, and the gas outlet 17 is connected to a cyclone 33.

The cyclone 33 is connected to a feed hopper 31, which is connected to a silicon particle supply system 40 that supplies metal silicon particles from the outside. A hydrogen chloride gas introduction means 20 for introducing hydrogen chloride gas into the inside of the device body 11 is provided on the underside of the device body 11. The hydrogen chloride gas introduction means 20 includes a gas chamber 21 in which hydrogen chloride gas is stored, and a gas supply port 22 for supplying hydrogen chloride gas into the gas chamber 21. Here, the gas chamber 21 is separated from the inside of the device body 11 by the bottom plate portion 13 of the device body 11.

The characteristic configuration of the fluidized bed reactor 10 of this embodiment is that a heat transfer medium particle supply system 41 is connected to the silicon particle supply system 40 to supply heat transfer medium particles.

Next, a method for producing trichlorosilane using the fluidized bed reactor 10 configured as described above will be described. Metallic silicon particles are supplied from the silicon particle supply system 40 to the feed hopper 31. Heat transfer medium particles are supplied from the heat transfer medium particle supply system 41 to the feed hopper 31 via the silicon particle supply system 40. The silicon particles and heat transfer medium particles are introduced from the feed hopper 31 through the valve 32 into the carrier gas introduction pipe 30 for introducing carrier gas, and are supplied to the inside of the device body 11 through the particle supply port 15 by airflow transport and mixed. At this time, hydrogen chloride gas is used as the carrier gas for airflow transport. The carrier gas is introduced at a constant pressure.

Hydrogen chloride gas is introduced into the device body 11 by the hydrogen chloride gas introduction means 20. The hydrogen chloride gas is sprayed into the device body 11 via hydrogen chloride gas spray members (not shown) arranged in a plurality of positions on the bottom plate portion 13 of the device body 11, and the sprayed hydrogen chloride gas is introduced into the mixed particles of metal silicon particles and heat transfer medium particles.

In this way, hydrogen chloride gas is sprayed onto the metal silicon particles inside the device body 11, causing the metal silicon particles and heat transfer medium particles to flow inside the device body 11. As the metal silicon particles come into contact with the hydrogen chloride gas while flowing, the metal silicon particles and the hydrogen chloride gas react at a predetermined temperature to generate trichlorosilane gas. Meanwhile, the heat transfer medium particles flowing together with the metal silicon particles absorb the heat generated by the reaction between the metal silicon particles and the hydrogen chloride gas due to their thermal conductivity, and by flowing throughout the entire furnace, they suppress local temperature increases in the furnace and play a role in maintaining thermal uniformity.

The trichlorosilane gas produced is taken out from the gas outlet 17 provided on the top plate 14 of the device body 11 and supplied to the subsequent process. In addition, unreacted metal silicon particles inside the device body 11 are discharged from the gas outlet 17 together with the trichlorosilane gas, recovered in the subsequent process cyclone 33, supplied to the feed hopper 31, introduced into the carrier gas introduction pipe 30, and supplied again into the device body 11. Metal silicon particles not recovered by the cyclone 33 are removed by the subsequent process filter 34.

Here, the characteristic heat transfer medium particles of this embodiment will be described in detail. The heat transfer medium particles have a smaller average particle size than the metal silicon particles, a larger density than the metal silicon particles, are inactive to hydrogen chloride gas, and are non-hygroscopic. Specifically, the heat transfer medium particles preferably have an average particle size smaller than the metal silicon particles having an average particle size of 200 μm to 500 μm and 10 μm or more. If the heat transfer medium particles have an average particle size larger than the metal silicon particles, they are less likely to flow in the fluidized bed reactor, and if they are less than 10 μm, they are more likely to be discharged from the gas outlet 17 shown in FIG. 1 together with the carrier gas to the outside of the device body 11. In either case, the heat transfer medium particles reduce the thermal conductivity, the function as a heat transfer medium is inferior, and local temperature increases in the furnace are more likely to occur. It is more preferable that the average particle size of the heat transfer medium particles is 10 μm to 499 μm. Here, the average particle size of each of the metal silicon particles and the heat transfer medium particles is the average value measured by a laser diffraction type particle size distribution measuring device (Microtrac: MT3300).

The heat transfer medium particles have a higher density than the density of metal silicon at 20°C (2.336 g/ ^cm3 ). Since the particle size of particles that can flow in the fluidized bed is within a certain range, particles with a particle size that is too large generally do not flow, and particles with a particle size that is too fine are discharged outside the device body together with the carrier gas. However, if the particle has a density higher than that of metal silicon, even relatively fine particles can remain in the fluidized bed without being discharged. For this reason, the density of the heat transfer medium particles that is preferable for flowing the heat transfer medium particles together with the metal silicon particles is preferably 3 g/ ^cm3 to 16 g/ ^cm3 , and more preferably 5 g/ ^cm3 to 10 g/ ^cm3 .

The heat transfer medium particles are inert and non-hygroscopic, meaning that they do not react or form compounds even when they come into contact with hydrogen chloride gas in the fluidized bed reactor. If the heat transfer medium particles were active with hydrogen chloride gas and reacted with the gas to form compounds, the yield of trichlorosilane would decrease. Non-hygroscopic heat transfer medium particles also do not form clumps and do not reduce flow, even if residual moisture in hydrochloric acid or water adsorbed on the surfaces of metal silicon particles adheres to the heat transfer medium particle surface in the fluidized bed reactor.

Examples of heat transfer medium particles having such characteristics include iron particles, or iron compound particles mainly composed of iron containing one or more elements selected from the group consisting of oxygen, chromium, and nickel.Other heat transfer medium particles include tungsten carbide particles, zirconium oxide particles, silicon carbide particles, aluminum nitride particles, mullite particles, and alumina particles.
The density, activity against hydrogen chloride gas, and moisture absorption of representative heat transfer medium particles among the above heat transfer medium particles are shown in Table 1 below. The activity of the particles against hydrogen chloride gas in Table 1 was determined by analyzing the heat transfer medium particles taken out of the furnace after the chlorination reaction was completed by X-ray diffraction. When no chloride peak was observed, which indicates the formation of a compound, it was determined to be "inactive", and when a chloride peak was observed, it was determined to be "active". The moisture absorption of the particles was determined by leaving the particles at 22% relative humidity and 25°C for one day, and measuring the moisture content according to the Japanese Pharmacopoeia, General Test Method, and Moisture Measurement Method (Karl Fischer method). When the increase in moisture content was 0.01% or less, it was determined to be "non-hygroscopic", and when it exceeded 0.01%, it was determined to be "hygroscopic".

The heat transfer medium particles are preferably supplied from the heat transfer medium particle supply system 41 to the silicon particle supply system 40 shown in FIG. 1 so that the heat transfer medium particles are 1% to 3% by volume when the total particles constituting the fluidized bed in the fluidized bed reactor are 100% by volume. When the content ratio of the heat transfer medium particles is calculated taking into account the density of the heat transfer medium particles, it is preferable to supply the heat transfer medium particles so that the heat transfer medium particles are contained in a ratio of 3% to 10% by mass when the total particles constituting the fluidized bed in the fluidized bed reactor are 100% by mass. If the content ratio is less than the lower limit of the above range, it is difficult to function as a heat transfer medium to suppress local temperature increases in the furnace. If the content ratio exceeds the upper limit of the above range, the proportion of metal silicon particles is relatively reduced, the reaction efficiency between the metal silicon particles and hydrogen chloride gas is deteriorated, and the amount of unreacted hydrochloric acid is likely to increase.

Next, we will explain in detail the examples of the present invention along with comparative examples.

Example 1
About 3000 kg of metallic silicon particles having an average particle size of 250 μm were supplied together with carrier gas via the silicon particle supply system 40, the feed hopper 31, and the particle supply port 15 into the apparatus body 11 of the fluidized bed reactor 10 shown in Figure 1, whose trunk 12 has an inner diameter of 800 mm. Hydrogen chloride gas was introduced from the gas supply port 22 of the hydrogen chloride gas introducing means 20 at a rate of 600 ^Nm3 /h, and the metallic silicon particles and the hydrogen chloride gas were reacted in the trunk 12. Particles having an average particle size of 10 μm or more produced by this reaction were collected from the gas outlet 17 into the cyclone 33 and returned to the feed hopper 31.

A portion of the gas generated within the device body 11 was sampled, and the components contained in the gas were analyzed every 10 minutes using a gas chromatograph (manufactured by J Sciences, model GC7000T). The yield of trichlorosilane on the first day was approximately 84% by mass. After this, the above analysis was performed twice a week.

From the second day onwards, iron particles made of metallic iron with an average particle size of 50 μm were supplied as heat transfer medium particles from the heat transfer medium particle supply system 41 into the device body 11 in conjunction with replenishing the metallic silicon particles consumed in the reaction. An increase in the trichlorosilane yield was observed when the supply of iron particles reached approximately 10 kg. In the first week, when the cumulative supply of iron particles reached 20 kg, the trichlorosilane yield further increased to nearly 88% by mass.

The same iron particles were continuously supplied into the device body 11, accompanied with the metal silicon particles consumed in the reaction. At the time of the second week, when the iron particles were supplied in a cumulative amount of 30 kg, the yield of trichlorosilane rose to nearly 90% by mass. Thereafter, from the third week to the sixth week, the yield of trichlorosilane increased and decreased by about 90% by mass, and from about the fifth week, when the cumulative amount reached 35 kg, an increase in unreacted hydrochloric acid was observed. For this reason, the supply of iron particles was stopped when the cumulative amount of the supply reached 45 kg, and the supply of hydrogen chloride gas was also stopped. After the temperature of the device body 11 was lowered to 60° C., the metal silicon particles remaining in the device body 11 were collected, and the iron particles present in the metal silicon particles were collected with a magnet. As a result of measuring these particles, the content ratio of iron particles in the metal silicon particles at this time was about 3% by volume.
FIG. 2 shows the yield of trichlorosilane (TCS) from the first day of starting the analysis of the components contained in the gas components until the sixth week, together with the yields of silicon tetrachloride (STC) and dichlorosilane (DCS).

<Comparative Example 1>
From the second day onwards, metal silicon particles having an average particle size of 250 μm were continuously supplied and hydrogen chloride gas was continuously introduced to react with the metal silicon particles and the hydrogen chloride gas in the same manner as in Example 1, except that the heat transfer medium particles were not supplied into the apparatus body 11. The yield of trichlorosilane in the sixth week after the start of the supply was about 84 mass%.

Table 2 below shows the characteristics when heat transfer medium particles of Example 1 were supplied and the characteristics when heat transfer medium particles of Comparative Example 1 were not supplied, as well as the trichlorosilane yield and its improvement rate in Example 1 and Comparative Example 1. The improvement rate of trichlorosilane yield was calculated by the following formula (1), where the trichlorosilane yield before the heat transfer medium particles were supplied is X mass % and the trichlorosilane yield after the heat transfer medium particles were supplied is Y mass %.
Trichlorosilane yield improvement rate (%) = [(Y-X)/X] x 100 (1)

As is clear from Table 2, in Comparative Example 1, since no heat transfer medium particles were used at all, the trichlorosilane yield on the first day of starting the reaction between the metal silicon particles and hydrogen chloride gas was low at about 84% by mass, and the trichlorosilane yield after six weeks was also unchanged at about 84% by mass, with an improvement rate of 0%.

In contrast, in Example 1, the particles mixed with the metal silicon particles were heat transfer medium particles that satisfied the requirements of the first aspect of the present invention, so the trichlorosilane yield on the first day was 84 mass%, while the trichlorosilane yield on the sixth week was 90 mass%, with the improvement rate being 6.7%. Iron compound particles containing iron as the main component and containing one or more elements selected from the group consisting of oxygen, chromium, and nickel other than the iron particles used in Example 1, or tungsten carbide particles, zirconium oxide particles, silicon carbide particles, aluminum nitride particles, mullite particles, and alumina particles also satisfy the requirements of the first aspect of the present invention in the furnace, and are therefore highly likely to improve the trichlorosilane yield.

The manufacturing method of the present invention can be used to improve the yield of trichlorosilane.

REFERENCE SIGNS LIST 10 Fluidized bed reactor 11 Apparatus body 12 Body 13 Bottom plate 14 Top plate 20 Hydrogen chloride gas introduction means 30 Carrier gas introduction means 31 Feed hopper 40 Silicon particle supply system 41 Heat transfer medium powder supply system

Claims (3)

1. A method for producing trichlorosilane by reacting silicon metal particles with hydrogen chloride gas in a fluidized bed reactor, comprising:
heat transfer medium particles having an average particle size smaller than that of the metallurgical silicon particles, a higher density than the metallurgical silicon particles, being inactive to the hydrogen chloride gas, and being non-hygroscopic are mixed with the metallurgical silicon particles in the fluidized bed reactor ;
13. A method for producing trichlorosilane, wherein the heat transfer medium particles are iron particles or iron compound particles mainly composed of iron and containing one or more elements selected from the group consisting of oxygen, chromium, and nickel . 2. The method for producing trichlorosilane according to claim 1, wherein the average particle size of the metal silicon particles is 200 μm to 500 μm, and the average particle size of the heat transfer medium particles is smaller than the average particle size of the metal silicon particles and is 10 μm or more. 3. The method for producing trichlorosilane according to claim 1, wherein the heat transfer medium particles are mixed with the metal silicon particles in a ratio of 1 volume % to 3 volume % when the total volume of particles constituting the fluidized bed in the fluidized bed reactor is 100 volume %.

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